Linköping University | Department of Computer and Information ScienceMaster thesis, 30 hp | Product development

Spring semester 2017 | LIU-IDA/LITH-EX-A–17/034–SE

Upper body ergonomics in virtualrealityAn ergonomic assessment of the arms and neck in virtualenvironments.

Filip Nilsson

Supervisors:Thom Persson, Sahand SadjadeeExaminer:Erik Berglund

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c© Filip Nilsson

Abstract

In Virtual Reality (VR), the body is often used as input in VR, having a healthyworking posture is important for long session in VR. To assess how severe differ-ent interaction methods are for the body, user tests was done in VR. 14 peopleparticipated and tested six manipulation controls which operate in different ways.Their hands’ and neck’s position and orientation was measured throughout thetest, and from this data characteristic body postures for each control setup waschosen. These were evaluated with RULA. How great the wrist angle is can havean effect on the severity of the posture. Also whether or not the arm is to theside or across the midpoint of the body should be taken into consideration. Whenaccounting for both the hands and neck, one of these have to come outside theircomfortable zone if the hands are supposed to be seen by the user in VR.

Keywords:Virtual Reality, ergonomics, RULA

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Preface

This thesis was done for RISE interactive and on the Department of Computerand Information Science (IDA) at Linköping University. Throughout this thesis,several people have helped and supported me. I would like to acknowledge themhere:

Thom Persson from RISE interactive for the opportunity to work in this area,inspiring suggestions for how the work could progress and feedback along the way.

Erik Berglund for helping to define the thesis and examining it.

Sahand Sadjadee for help and support throughout the whole thesis.

August 15, 2017Filip Nilsson

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Contents1 Introduction 1

1.1 Goal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Research questions . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 Literature review 32.1 Ergonomics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3 Virtual Reality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.4 Ergonomics in VR . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 Method 133.1 Participants and setup . . . . . . . . . . . . . . . . . . . . . . . . . 133.2 Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.3 Test software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.4 Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

4 Result 244.1 User tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.2 RULA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.3 Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5 Discussion 365.1 Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365.2 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

6 Conclusions 416.1 Future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

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List of Tables1 Percentiles, lengths [11] . . . . . . . . . . . . . . . . . . . . . . . . . 42 Percentiles, rotations and angles [12] . . . . . . . . . . . . . . . . . 43 Number of times limit breached . . . . . . . . . . . . . . . . . . . . 244 Maximum value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 RULA poses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 RULA poses, exaggerated . . . . . . . . . . . . . . . . . . . . . . . 287 RULA final score . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 RULA final score exaggerated . . . . . . . . . . . . . . . . . . . . . 29

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List of Figures1 Work flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 A participant during a test . . . . . . . . . . . . . . . . . . . . . . . 133 The area used during the test . . . . . . . . . . . . . . . . . . . . . 144 The test environment with the cube . . . . . . . . . . . . . . . . . . 145 The cube and reference plane . . . . . . . . . . . . . . . . . . . . . 156 The big circles on the controllers are the thumbpads . . . . . . . . . 167 The manipulation menu . . . . . . . . . . . . . . . . . . . . . . . . 168 The manipulation sphere . . . . . . . . . . . . . . . . . . . . . . . . 179 The small cube closest is the avatar . . . . . . . . . . . . . . . . . . 1810 The cube is position in the direction that the controller is pointing . 1811 The graphics for the pull manipulation . . . . . . . . . . . . . . . . 1912 Each point represents the user being over the limits . . . . . . . . . 2013 Each point represents the user being over the limits . . . . . . . . . 2114 The colors shows which manipulation setup is active and if it is a

warm up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2115 The colors shows which manipulation setup is active and if it is a

warm up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2216 The viewing volumes seen from an angle . . . . . . . . . . . . . . . 3017 The viewing volumes seen from the side . . . . . . . . . . . . . . . . 3118 The viewing volumes seen from the front . . . . . . . . . . . . . . . 3119 The working volumes seen from an angle . . . . . . . . . . . . . . . 3220 The working volumes seen from the side . . . . . . . . . . . . . . . 3321 The working volumes seen from the front . . . . . . . . . . . . . . . 3322 The viewing and working volumes seen from an angle . . . . . . . . 3423 The viewing and working volumes seen from the side . . . . . . . . 35

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Nomenclature

FOV Field of viewHMD Head-mounted displayOWAS Ovako Working posture AssessmentRULA Rapid Upper Limb AssessmentVR Virtual Reality

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1 Introduction

Virtual Reality (VR) has had an upswing in popularity in recent years. It is anintuitive and exiting way to interact with computers. But it also has its drawbacks.Using movements as input can lead to fatigue. It may also force users to takeuncomfortable or even damaging postures. All these effects can reduce the playtimein VR.

Several different reports has noted that people get tired quickly after using theirbody to interact with a computer [1, 2, 3]. It is possible to build an infiniteunconstrained world in VR, but how can it be design to allow for longer playtimein regards to fatigue and comfort?

The purpose of this thesis is to find ergonomic design aspects in VR which allowsthe user to spend longer sessions in VR and with less strain on the body. This willgive the user a better experience and a more efficient way to utilize the software.

1.1 Goal

The result of the project will be a basis for designing ergonomic virtual environ-ments in regard to the neck and arms. These will be based on anthropometric dataand user tests.

1.2 Research questions

The questions studied in this thesis are:

• Q1. Which anthropometric measurements are relevant to construct an er-gonomic environment for the neck and arms in virtual reality?

• Q2. How should an ergonomics virtual environment in regard to the arms bedesigned?

• Q3. How should an ergonomics virtual environment in regard to the neck bedesigned?

• Q4. What ergonomic implications arises when considering both the neck andarms in virtual reality?

Q1 will be answered with a literary review concentrating on anthropometrics andprevious studies on ergonomics in VR. The data acquired from answering Q1 willbe used in combination with results from the user tests and a literary review onVR hardware to answer Q2 and Q3. The answers from Q2 and Q3 will then be putagainst each other to answer Q4. To have a base to analyse results from the usertest a literary review on ergonomic evaluation methods will be done. A graphicalrepresentation of the workflow can be seen below in figure 1.

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Figure 1: Work flow

1.3 Scope

There is a wide variety of VR hardware today. This project will be using the HTCVive, as this system is available at Linköping University. There are also alternativeswhen it comes to development software. Unity in combination with c# has beenchosen. This because the writer has experience with this software before and forits VR support.

This report will focus on physical ergonomic aspects. As most VR hardware todaytake user input from the neck and arms, the focus in this thesis will be on thesebody parts. Cybersickness is not covered in this report.

1.4 Background

The work this thesis is based on was done for RISE Interactive in Norrköping.They are an applied science institute, working in areas such as 3D, interaction,prototype development and VR.

RISE interactive want to evaluate diverse ways to interact in VR. This led to auser study testing ways to manipulate objects in VR. For this thesis, ergonomicmeasurements were done during the test. For RISE Interactive, the participants’precision and completion time was taken and compared.

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2 Literature review

The literature review encapsulates four areas: ergonomics, methodology, virtualreality and ergonomics in virtual reality. These will be presented in separate subchapters.

2.1 Ergonomics

This chapter will firstly go through basic concepts regarding ergonomic and thenbring up specific ergonomics considerations to different body parts.

2.1.1 Ergonomic concepts

The International Ergonomics Association defines ergonomics as “Ergonomics (orhuman factors) is the scientific discipline concerned with the understanding ofinteractions among humans and other elements of a system [...] in order to optimizehuman well-being and overall system performance” [4]. They divide ergonomicsinto three sections:

• Physical ergonomics

• Cognitive ergonomics

• Organizational ergonomics

Physical ergonomics concerns for example posture and body movements whereascognitive ergonomics involves for example human-computer interaction and stress.Organizational ergonomics handles for instance teamwork and communication.Brinkerhoff focuses on bettering the efficiency and quality of the work by designingthe “Job, equipment and workplace” [5]. The science behind this is ergonomics.The Swedish work environment authority agrees, but also lays weight to a holisticview and that planning has a big part when working with ergonomics [6].

The science behind the length and dimensions of body parts is called anthropom-etry [7, 8]. These measurements are for the most part normally distributed [9,10]. A set part of the population can be described with percentiles. If a space isdesigned for the 95th percentiles in mind, then the largest 5 percent of the popu-lation won’t fit [9]. A general rule is that x percent of the population are shorterthan the x th percentile [10]. To make sure that a great deal of the populationis considered, the 5th percentiles and 95th percentiles measurements are used [9].This encapsulates 90 percent of all people. Anthropometric data can be dividedinto static and dynamic. Static data are measurements on the body, for examplesomeone’s height. Dynamic data consists of reach and operating space.

There are a lot of anthropometric data from the military [8]. They have a lot ofsamples and the data is exhaustive. The data is collected from one specific group

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of the population, and doesn’t necessarily mirror the whole population [10]. In thetables below, (table 1 and table 2) data is presented from the MIL-STD-1472G [11]and NASA–STD–3000/T [12] respectively.

Table 1: Percentiles, lengths [11]

5 percentile female [cm] 95 percentile male [cm]Functional reach 73.5 94.2Elbow (radiale) height 97.5 115Chest (nipple) height 115 136.9Eye height (standing) 150.1 175.6Stature 161.2 187.8Eye height sitting 72.3 86.2Shoulder height, sitting 50.9 64.6Elbow-grip length 30 39.1Elbow-fingertip length 40.6 52.4Elbow rest height* 19.5 20.1Shoulder-elbow length 32.9 40.1Foot length 23.3 29.2Shoulder (bideltoid) breadth 38.2 53.5

*This measurement is 26.9 cm for 95th percentile females and 28.2 cm for 5thpercentile males.

Table 2: Percentiles, rotations and angles [12]

5 percentile female [cm] 95 percentile male [cm]Shoulder, rotation lateral 53.8 96.7Shoulder, rotation medial 95.8 126.6Neck, rotation right/left* 74.9 99.6Neck, extension 4.9 103Neck, flexion** 46 71

* Small deviation between left and right.** The neck flexion for 95 percentile females is 84.4 cm

The Oxford Dictionary defines fatigue as: “A reduction in the efficiency of a muscleor organ after prolonged activity” [13]. NASA defines it as: “Weariness, exhaustion,or decreased attention related to labour, exertion, or stress. This may also resultfrom lack of sleep, circadian shifts, depression, boredom, or disease. These factorscan lead to a decreased ability to perform mental or physical tasks” [14].

There are four aspects to consider when looking at upper limb disorders and awork task [15]:

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• repetition

• working postures

• force

• duration of exposure

These are often all in effect together and they should all be considered then as-sessing the task. For example, can something with high force and bad posture beacceptable if the duration is short.

2.1.2 Ergonomics for specific body parts

The head has comfortable and maximum range for head turning and bending [16].The comfortable degrees are:

• Left and right: 30

• Up: 20

• Down: 12

The maximum degrees are:

• Left and right: 55

• Up: 60

• Down: 40

An angle greater than 25 degrees down forces the neck to constantly work to keepthe head up [8]. A bent neck also heightens the risk for pains and diseases [9].

The angle of the neck doesn’t alone determine how much the player can see in thevirtual world. Field of view (FOV) also plays a big part. Field of view is what astatic eye can see, measured in degrees [14]. The FOV of one eye is 150 horizontallyand 190 for two eyes. The vertical FOV is 125 for both cases. In contrast to FOV,Field of regard is what an eye can see when head and eye movement is considered.But the FOV isn’t determined by the eye when using a head-mounted display(HMD). A HMD has a limit to how much the user can see, as it has its own FOV.The HTC Vive has a field of view of 110 degrees [17].

The eyes are important to take into regard when designing for the neck. Whenthe eyes are relaxed they are angled down 10-15 degrees [10]. The area which isoptimal for looking is between 0 to 30 degrees down [10, 8], and they can be angled24-27 degrees down before the neck bends. The eyes’ focus area reaches 5 degreesfrom the focus center of the visual field. This is the only part of the vision thatcan be used to read. If any interface is placed within 1/3 of the viewing field, theydon’t have to whirl their eyes [18]. Reading a text which is 90 degrees to the line

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of sight is preferable, but if a work space is angled then things might glide off it[8].

Looking at something close to the eyes is fatiguing. The minimum distance is 500mm [10]. The eyes’ lenses are relaxed if they are looking at something more than6 meters away. Kroemer states that the preferable position for something that theeyes are focusing on is at 40-80 cm [8]. If everything is in focus in the VirtualWorld simultaneously, the user can get eye strain [18].

Things which are too close to the eyes can cause double vision, shorter than onemeter [16]. There is a risk of eye strain if someone is looking at something for toolong at 1-10 meters in VR. This risk is less when the distance is greater. After 20meter the 3D effect is small in VR.

Muscles fatigue if the they work to keep the body in a static position [19]. Staticload is a prolonged continuous load when the muscle and force is static [9]. Greaterstatic load can lead to fatigue, pain and lactic acid accumulation in a muscle group.Lactic acid accumulation can quickly be acquired by having an arm straight out.

Keeping the arms and shoulders at a heightened position puts a lot of static loadon the neck and shoulder [20]. It heightens the risk of diseases and pains [9]. Theyalso get fatigued if the arm is high or behind the body [19]. The upper armsshould be close to the body and the hands should not be above the shoulders for aprolonged time [9]. The upper arms should not be angled out more than 30 degreesfrom the body [20].

To ensure that the shoulders are low, the working area should be at elbow level[20]. This also allows the upper arms to be along the body. To be more precise,precision work should be 50 to 100 mm above the elbow, and light work 50 to 100mm below [9]. The hands are the most mobile in the area between the hip andelbows [8]. Precision work in which the sight is important, a tilted surface 30 to 50centimetres from the eye is preferable [20]. It also makes a support for the arms.

The length from the tip of the thumb to the elbow is called “normal reach” [19].Persistent operations should be confined to the normal reach. A maximum reachis where no tasks should be outside off. It is limited to what can reached with thetorso not flexing.

Large wrist angles cause wrist pain [9]. To allow the hand to work in a suitableangle when using tools, the tools’ handles should be inclined by 70 degrees inrelation to the work vector [9, 15]. The wrist should be in a handshake position[15]. Any deviation may be a risk, and repetition of the movement may worsen therisk. The hand has the most strength in this position [10]. And it also wears lesson tendons in the forearm which controls the hand, when the hand is bent.

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2.2 Methods

Data that is collected can either be objective or subjective [9]. Subjective data isthe participants’ own judgments, whereas objective data is gathered by measure-ments. A mix between the two are semi-objective, there an assessment is donebased on subjective data. A small part is observed with objective data. Subjectivedata captures more of the experience. Below are several subjective and objectivemethods presented.

2.2.1 Subjective methods

The NASA Task Load Index subjectively measures the following [21]:

• Mental Demand

• Physical Demand

• Temporal Demand

• Performance

• Effort

• Frustration

These factors are combined to rate the workload on human-machine interfaces[22]. Each of these factors gives separate information on the assignment, whichmakes TLX provide information that other methods don’t. It takes less than threeminutes to collect the data. TLX is the most popular measurement for workload[23]. (This can be because of the Matthew effect.)

Borg has developed two subjective measurements which can be used to access er-gonomics, the Borg RPE scale and Borg CR-10 scale [9]. In both methods partici-pants rate their fatigue on a numbered scale with corresponding words, describingthe fatigue at different levels with rising intensity. The reason the methods in-cludes both words and numbers is so it can be easier to rate [24]. From the BorgRPE scale an estimation of the participant’s heart rate can be done [9]. To useheart rate to find dangerous levels of strain may not be perfect as psychologicaland physical factors can affect the test [24]. To get a better picture to find dan-gerous strain, many more factors than heart rate must be considered, for examplebody temperature changes and blood pressure elevation. It has also been notedthat the conversion from the RPE scale to heartbeat isn’t fully accurate. Thereare differences between people and the age can also play a part [24]. A greaterresponse in the RPE scale has been recorded if participants were asked more fre-quently during the test [25]. This effect diminishes after time. The PRE-scale isbetter suited when testing extension and CR-10 should be applied when testingindividual symptoms [24]. The Borg CR-10 scale can be used to evaluate morethan fatigue [9].

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2.2.2 Objective methods

A objective approach to review posture is to measure it [9]. It can be done withrulers and protractors. A more high-tech approach is to use motion-capture orvideo. These techniques make it possible to analyse movements.

The OWAS system is used to evaluate body postures at heavy lifts [9]. The OWASmethod includes around 80 postures with regard to legs, arms and back [26, 27,9, 28]. The load is also incorporated. For each of the body parts (legs, arms andback) there are a set of postures which has a number associated with it [28]. Forthe arms, there are three cases or postures: Both arms under the shoulders, botharms over the shoulders and one arm over the shoulders. The legs’ postures scalesfrom sitting to standing to walking i seven step. The load is also divided intocategories, namely: equal or less than 10 kg, more than 10 and equal or less than20 kg and finally more than 20 kg.

Based on the numbers from the different body parts and load, the result is oneof four categories [28, 26]. These tell how hazardous the posture is. An action isassociated with each category, from “No actions required” to “Corrective actionsfor improvement required immediately”.

The duration in which the poses are held during the observation can also be usedto risk asses a work task [28]. This evaluation looks at the percent of time eachposture is held for the different body parts individually. For example, how muchof the time is spent sitting or with the arms over the shoulder. It results in thesame four categories as above.

To have a reliable result the sampling interval should not exceed 30 seconds [29].More observations should be done if the sampling interval is large to decrees theerror. The different poses for the body parts are quite wide [27]. For example, are90 degrees and 30 degrees of the knees considered the same.

RULA evaluates body posture with regard to seven parts of the body, with focuson the arms [9]. RULA differentiates between static and dynamic movements. Theweight is also considered.

RULA was developed so that it didn’t require extensive training to be performed[28]. A RULA investigation doesn’t need any equipment except for a pen [30].The data collected comes mainly from observations of the work task that is beingevaluated [28].

During an observation, the limbs that are the most used or has the greatest jointangles are analysed [28]. The observations are given a score and are marked in atable depending on their severity. For example, does a wrist angle over 15 degreesequals 3 points and a neutral wrist equals 1 points. When the posture of all bodyparts, how much they are used and the force that is exerted on them is addedtogether, a grand score in given in the range 1 to 7 [30, 28] RULA gives a clearconnection between the postures and final score [30]. This score is converted into

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a action level from 1 through 4 [28].

Action level 1: “A score of one or two indicates that posture is acceptable if it isnot maintained or repeated for long periods”

Action level 4: “A score of seven or more indicates investigation and changes areare required immediately”

RULA only mentions loads on two occasions and the available alternatives arebroad [31]. If the work is repetitive is also only mentioned two times. Most of thetables handle body posture. This makes RULA suited to evaluate static postureswith low load and repetition. RULA has a strong focus on posture, but a weakfocus on force, repetition and duration.

The result of both RULA and OWAS is recommendations if something shouldchange or not [9]. RULA only takes two states of balance into consideration (bal-anced and unbalanced), whereas OWAS takes more [32]. This can make RULAless accurate when assessing unbalanced postures. OWAS underrates the hazardsof posture in comparison to RULA. This effect occurs in diverse kinds of tasks.

2.3 Virtual Reality

In this chapter, the term Virtual Reality will be explained. Relevant hardware willalso be described.

2.3.1 Define Virtual Reality

A virtual reality system submerges the user in a virtual world [33, 34, 35, 36].The player can interact with the virtual world, through devices which location andorientation are tracked by the system [33, 34, 35, 36]. The user gets feedback ofvarious kind, it may be visual, auditory, haptics [33, 37]. The interaction betweenthe user and system happens at once, the system reacts directly at input and thefeedback is sent back just as quick [37]. The distinct part in the system is the user,computer and the interface between user and computer [35]. One part of inputwhich is often mention is the ability to adjust the viewpoint within the virtualworld [34]. By changing this, the user can see different parts of the world, andobjects in it will stay positioned as they would in the real world because they areindependent from the viewpoint [35].

2.3.2 Head-mounted display

To convey the view to the user a head-mounted display (HMD) is often used [38].It is a display placed close to the eye and strapped to the user’s head [36, 35]. Itencapsulates the whole user’s vision field [36, 39]. The location and orientation

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of the HMD, and thereby the user’s head, controls the view within the virtualenvironment and it is updated directly [39, 38, 36]. A HMD is an input and outputdevice, it’s position is tracked and sent to the computer and it sends images to theuser [37].

2.3.3 Input device

Input devices for Virtual reality systems can take many forms. They allow theplayer to interact with the virtual world [37]. There are different kinds of inputdevices for Virtual reality systems [40]. Controllers are hand held and have sev-eral ways the player can interact with the virtual world. They have buttons andjoysticks or touchpads [37, 40]. They come in pairs, one for each hand [40]. Opti-cal trackers use vision to decide the orientation and position of objects [37]. Thetracking is fast and allows a large workspace. Although the tracker doesn’t workif it is obstructed. An object’s change in velocity and orientation can be measuredwith inertial trackers. They don’t need anything from the outside to work and cantherefore not be obstructed. They build up an error as time goes by. A hybridsystem combines several ways to track objects [37].

2.3.4 HTC Vive

HTC Vive is a Virtual reality headset. It consists of a headset with a screen andtwo controllers [41]. Vive’s controllers have touchpads [40]. The HTC Vive useslighthouses to track the devices. The lighthouse shoots lasers into the tracked areaand all devices registers when the laser intersects with them. This system grantsthe user the possibility to move around while using the Vive, in an area of 5 squaremeters. A majority of the VR-systems are intended to be used while seated.

The Vive’s HMD is 19 cm wide, 12.7 cm high and 8.9 cm (deep) [42]. It weights563g and the two controllers weight 406g combined. There are problems to focusor read text that are outside the centre of the (view field) [43].

2.3.5 Alternative hardware

Along with the HTC Vive several other Virtual Reality systems have been released.For example, the PlayStation VR [44] and Oculus Rift [45]. They all share nu-merous features. All of them consists of a HMD and two controllers [41, 44, 45].The technique which is used to track the devices are different and the controllersare distinct to the system. As mention above the HTC Vive can be played whilewalking around in a small area. The PlayStation VR and Oculus are intended tobe played sitting down [40].

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2.4 Ergonomics in VR

This chapter presents results from previous studies in the subject area.

A study evaluated different VR systems regarding ergonomics [46]. It measured thelevel of discomfort or pain in several body parts after 20 minutes of usage. Three ofthe four evaluated systems used a HMD. Only these systems reported discomfortat the head, but all four reported discomfort in the neck. For the systems with aHMD, this was because of the weight of the HMD and that the software requiredthe user to look around. A system with limited FOV heightens the issue by forcingmore and greater head movements from the user. Another source of the neckproblems was that in one system, the user was forced in this particular programto look up for long periods.

One other study found a workaround for placement of graphics. It tested a gesturebased input system, where the user’s body also worked as a canvas to displaygraphics on [47]. If only one hand is needed for input then the other can insteadbe used as the display. This way the display hand can be in a comfortable positionbecause it doesn’t have to do other inputs. It also frees the input hand from whereit can be and how fast it can be moved because the user doesn’t have to readanything on it. It doesn’t have to be in the visual field.

When a controller is visualized in the virtual world the user will often keep it sothey can see it when they are using its button’s [46]. Even though this is not arequirement to use the device. Remembering the controls is also an obstacle fornew users [46, 48]. This is true for both movements and buttons and have beennoticed in different VR-systems.

Using a mid-air controller is harsh on the shoulder [46]. In a study where differentcontrollers where used, the mid-air control s reported more frequent and more severdiscomfort in the shoulders. This effect may come from that the software for oneof these setups required the user to extend their arm to interact with menus for anextended period of time.

When the arm is further from the body the moment it exerts on the body becomesgreater. This means that interactions which are at a distance from the body ismore tiring than close interaction. Tests show that if users must move their armcontinuously and keep it outstretched, they get little fatigue after about 10 minutesof play in VR [1]. The best placement of a 2D interaction area is at a height betweenthe abdomen and the shoulders, closer than 35 cm to the body [3]. This allows theuser to have an bent arm and can keep it closer to the body.

An interaction interface in 3D compared to 2D is slower and more fatiguing [49]. 3Dallows for more commands because it covers more space. But the third dimensionsit adds is hard to have high fidelity in for the user [49, 48].

A third interaction method, ray-casting, allows the user’s arm to be low and closeto the body and only the wrist has to move [49]. It is less physically demanding

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than 2D mid-air interaction, but also less accurate. This stems from that the 2Dcontrols requires the user to move the arm more than pointing would.

A larger interaction area mid-air forces the user to move the arm more which inturn is more tiring [50, 3]. Though a larger area is faster to use and more accurate[3]. Different points in the interaction area are also more demanding to reach. Fora 2D plane in front of the user, the lower right corner is the least demanding andthe upper right corner the most demanding, for the left hand. These change sides ifthe right hand is used. If instead a volume around the player is used for interaction,points which are further away from the body and requires longer interactions aremore demanding [1].

Other interaction methods require no or little movement at all. If only the buttonson the controllers is needed then the arm can be kept still [51]. And if the user onlyhas to move their hand and wrist to interact then they get less fatigued compare toif the whole arm is used. In one study the participants went from using the wholearm to only moving the wrist because of fatigue.

There are also differences if one or two hands are used to interact. When only onehand is used, a selection method where the user holds the hand over an object ispreferred in regard to endurance [3]. If both hands can be used, then one handshould select the object and the other click on a button. Pressing the button andselection with the same hand may cause the controller to move when pushing thebutton, making the user miss [51].

One way to limit how much the user must move in VR is to incorporate a Con-trol/Display ratio (C/D). This ratio is how much the player has to move the con-troller to get the same movement in the virtual world [52]. A lower ratio amplifiesto movement in the game more. A lower C/D leads to lower perceived fatigue com-pared to a higher C/D. It also makes the user feel less tired after a VR session. Thisconcept of magnifying the user’s movement can also be applied to rotation. If anobjects orientation is copied of the controller, the user’s hand might be forced intoa bad posture [48]. An amplification of the controllers rotation may circumventthis.

If a 3D input system is not designed with ergonomics in mind it can harm themor their performance [53]. Problems with hand-held devices may be mitigated bystructuring the software so it avoids static postures and by the users getting moreexperience with the hardware [46]. What kind of feedback the user gets in VR canaffect fatigue and discomfort [2]. The test groups which only got visual feedbackwere fatigued faster and reported more discomfort, compared with groups whichgot a combination of feedback (audio, visual, haptic). There was no significantdeviation between the other groups which got different combinations of feedback.There are also solutions outside the virtual world. If the setups is at an ordinarydesk, the user should be able to rest their arms [53]. Either on arm rests or at thetable. The shape of the table can increase this rest area.

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3 Method

A series of tests was done to highlight how users behave in VR in regard to er-gonomics. The test was constructed around different manipulation controls. Itwas presented as tasks in which the participants had to move, scale and rotateobjects to match a reference object in a virtual environment. Each test consistedof manipulating the object three time for every manipulation control. A shortwarm up time was given to familiarize with the controls before each controls setup.During the test, a software evaluated arm position as well as neck angels with theVR equipment and logged this data. This data was later used to evaluate theparticipants postures at different times during the test. Notes on how the partic-ipants were performing was taken during the test and comments taken from theparticipants.

3.1 Participants and setup

14 people participated in the test. Eight of them had a little experience of VRbeforehand, and two a lot of experience. The test took about 20 minutes. Duringthe test, the participants were seated and the HMD and both controllers were usedduring the whole test (see figure 2). Before the test started, each participant gotan introduction of the HTC Vive controllers and mainly the buttons. During thewarm up times, the participants got instructions for the current controls, and wasfree to ask questions. The test environment can be seen in figure 3.

Figure 2: A participant during a test

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Figure 3: The area used during the test

3.2 Task

In the test the user was required to move, scale and rotate a cube to fit a referenceplane. The plane spawned with a random position, scale and rotation within pre-determined limits. After the player had placed the cube three times, the programswitches to a new controller setup and starts the warm up. The user pushes a but-ton on the right controller to submit their answer (which is the current position,scale and rotation of the cube). This triggers the next plane to be spawned. Thisbutton also ends the warm up periods. The virtual test environment is shown infigure 4, and the cube and reference plane are shown in figure 5.

Figure 4: The test environment with the cube

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Figure 5: The cube and reference plane

3.2.1 Manipulation controls

The test consists of 6 manipulation controls. Each manipulation control allowsthe player to move, scale and rotate the cube. All six controls have uniform scale,all movement is two dimensional on a plane and all rotations happens around theupward axis. All controls utilize different approaches to highlight how the userworks in a range of designs regarding ergonomics.

The controls were designed and chosen together with RISE interactive. Therefore,they are not just chosen for ergonomic reason, but also to evaluate user experiencein a broad spectrum of approaches to manipulation in VR.

The Menu setup resembles how menus are often handled in VR applications. It isalso one of three controls which requires only one hand (the others being Sphere andDrag). The other remaining three (Thumbpad, Avatar and Pull) uses both hands.The movement required for each setup varies between the controls. Thumbpadonly uses the handles on the controllers, Sphere, Avatar and Pull only uses armmotions, whereas Menu and Drag uses both.

The controls are ordered form the one that was thought to be the least demand-ing to the one which was thought to be the most demanding. Below is a briefdescription of all the manipulation controls in the order they have in the test.

ThumbpadThis controller setup only uses the two thumbpads. The right one moves the cube.When the player moves their finger across it the cube moves in the same directionas the finger. The left thumbpad scales and rotates the cube. This is also doneby swiping a finger over the pad. If the movement is to the left or right over thepad the cube rotates, and if it is up or down the cube scales. The thumbpads aredisplayed in figure 6 below.

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Figure 6: The big circles on the controllers are the thumbpads

MenuThe Menu control setup uses raycast. A menu spawns in front of the player withbuttons and sliders that governs the cube, the menu can be seen in figure 7 below.The player can interact with the elements by pointing the right controller at themand pushing the "menu" button on the controller. The movement of the cube iscontrolled by four buttons: up, down, left and right. One push moves the cubea set distance in that direction. This distance can be changed with a slider. Therotation can be altered with two buttons (left and right) and also a slider. Thebuttons impact can be adjusted with a slider just as with the movement. The scaleis changed with a slider.

Figure 7: The manipulation menu

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SphereWhen this control is activated a sphere spawns around the left controller, the spherein shown in figure 8 below. While the controller is inside the sphere the cube’srotation follows the controller and its scale can be adjusted by moving a finger upor down on the thumbpad on the same controller. The rotation it doubled for thecube compared to the controller. If the controller is moved outside the sphere thecube moves in the vector the controller has to the centre of the sphere. The speedof the cube is determined by the distance between the sphere and controller.

The user has the option to reposition the sphere. By holding down the grip buttonon the left controller the sphere follows the controller.

Figure 8: The manipulation sphere

AvatarThis setup works on a master-slave mechanic. When activated, a copy (calledavatar) of the cube is spawned in front of the user, as displayed in figure 9. Theuser can attach it to a controller by moving inside it and holding the grip button.If the button is held the avatar will follow the controller. When the avatar is heldthe cube follows its movements and rotation. To scale the cube the player can gripthe avatar with both controllers and spreading them apart to scale it up, or putthem together to scale it down. The cube follows the avatars scaling.

Both the movement and scaling is amplified for the cube in comparison to theavatar.

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Figure 9: The small cube closest is the avatar

DragThis control setup places the cube in front of the right controller, and always keepsthe cube where the controller is pointing. The setup is shown in figure 10. Thedistance from the controller to the cube is determined by the distance between theright controller and the HMD. This means that by moving the arm forwards orbackwards in reference to the HMD, the cube follows that movement. The usercan rotate and scale the cube with the thumbpad on the right controller: Rotateby placing a finger on the left or right side, and scaling by placing a finger on thetop (scale up) or bottom (scale down) of the thumbpad.

The movement of the cube is scaled up compared to the movement of the controller.

Figure 10: The cube is position in the direction that the controller is pointing

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PullThis control setup utilizes the position of both controllers. When both grip buttonsare held down the movement of the controllers and their position relative to eachother controls the cube. The distance between the controllers affects the scale ofthe cube. Their relative position rotates the cube. Their combined movementmoves the cube.

A set of lines are attached to the controllers to illustrate the manipulations to theuser. One line represents the combined movement of the controllers. Another theirrelative position to each other. These can be seen in figure 11.

Figure 11: The graphics for the pull manipulation

3.3 Test software

During the test, Unity continually monitor the orientation of the HMD and theposition and rotation of the two controllers. This is done through a c# script inUnity. The program takes elbow height from the ground while sitting and forearmlength of the participant as input. This was measured on every participant witha folding ruler before the test started. The program has predetermined limits forcontroller height, distance between controller and HMD, and HMD rotations. Thelimits are derived from MIL-STD-1472G [11] and Chu [16].

The limit for controller height takes both controllers’ height and checks if it isabove the participants elbow height. The distance between controller and HMD ismeasured for both controllers and only on a 2D plane, and checks if the distanceis greater than the participants forearm length. The program doesn’t take intoconsideration the height difference between the controllers and HMD or in whichdirection a controller is relative the HMD. The rotations that is monitored of theHMD is how much is it angled up, down, and to the sides. These three different

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cases have independent limits. The limits for the controller positions (height anddistance to HMD) has a small margin of 15 cm, which the current value has toexceed as well as the limit.

If the player exceeds any of the limits, the program will log the event. For as longas the limit is exceeded by the user, the program will continuously save (at a setfrequency) the current parameter along with a timestamp. This data was savedto text files (one for each measured parameter) where each line was an entry withthe timestamp and value. The program also noted which control setup was activeat what time and when the player made an input. With this data, a time line foreach participant could be made which visualizes the ergonomic aspects at differenttimes during the test. An example of a time line can be seen in figure 12, 13, 14and 15.

Figure 12: Each point represents the user being over the limits

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Figure 13: Each point represents the user being over the limits

Figure 14: The colors shows which manipulation setup is active and if it is a warmup

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Figure 15: The colors shows which manipulation setup is active and if it is a warmup

3.4 Data analysis

In excel the number of times the limits was exceeded and the maximum value foreach monitored parameter was derived. The data was broken down more to showhow many times the limits were exceeded and what the maximum value for eachmanipulation control was. Scatter graphs displaying the monitored values for eachtest was also done in excel. The data from all test was combined to show a meanvalue. These values were then used to create a posture for each control setup.

One characteristic posture was chosen for each manipulation control to do a RULAevaluation on. These were based on the data gathered from the tests. A secondRULA evaluation was also done on exaggerated postures. These were based on theprevious postures but tuned up to become worst case scenarios.

These variables were kept the same for all RULA evaluations:

• Upper arm adjustment = 0, (exaggerated = 1)

• Arm muscle use = 1

• Force Load Score A = 0

• Trunk = 1, (exaggerated = 2)

• Trunk adjustment = 0, (exaggerated = 1)

• Wrist Twist = 1

• Legs = 1

• Upper body muscle use = 1

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• Force Load Score B = 0

All exaggerated poses had the:

• shoulders raised

• wrist bend from mid line

• neck twisted

• trunk angled forward (0-20 degrees)

• trunk twisted

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4 Result

The first part of this chapter presents results from the user study. The second partpresents results based on the literature review.

4.1 User tests

Below is the result from the user tests presented. First the data collected forthe software and then observations made during the tests and comments from theparticipants.

4.1.1 Data Collected from software

In the tables below (table 3 and table 4) is the data collected from the user testspresented. The values in the tables is the mean value calculated from all user tests.The first (table 3) displays the number of times that each limit was exceeded by theparticipants for each controller setup. For the parameters regarding the controllers,the values for both controllers have been added together. The second table (table4) shows the mean of the maximum value reached by each participant for eachcontroller setup. For the parameters regarding the controllers, the highest value ofthe two controllers are displayed.

Table 3: Number of times limit breached

Thumbpads Menu Sphere Avatar Drag PullAngle Down 258.8 1533.5 1092.4 502.7 319.1 419.5Angle Left 4.0 67.8 17.3 9.1 0.8 10.1Angle Right 0.6 1.0 0.4 1.8 3.5 2.3Controller Height 962.9 405.3 956.3 423.9 363.1 906.2Controller Distance 0.5 3.8 51.4 68.2 33.1 154.9

Table 4: Maximum value

Thumbpad Menu Sphere Avatar Drag PullAngle Down 24.84 42.34 43.46 37.48 18.89 30.06Angle Left 19.03 43.60 34.01 35.01 9.54 31.58Angle Right 6.46 6.10 4.54 6.90 15.71 20.17Controller Height 0.21 0.14 0.33 0.22 0.13 0.29Controller Distance 0.04 0.10 0.52 0.43 0.37 0.66

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ThumbpadThumbpad had the least number of limits reached for HMD angle down. If thevalue of limit reached for controller distance is combined for both controllers, thenit got least there also. The limit for controller height was breached the most timesfor Thumbpad by a thin margin. It had almost the same amount for both hands.

The size of the HMD angle down was relatively low compared to other manipula-tions. This was also true for controller height. As the limit for controller distancewas almost never reached, the mean max value was neglectable.

MenuMenu had the most violation for HMD angle down and to the left by a big margin.It had the greatest angle to the left and it had almost the largest angle down.The limit was not reached much and it had a very low max value for controllerdistance. The controller height limit was breached a combined 400 times and hada maximum value of 0,14.

SphereThe combined times the controller height limit was reached was almost the most forSphere. It had the second most for HMD angle down, trailing by 50 percent. Forcontroller distance, it was in the middle, well below Pull and above Drag. AlthoughSphere did have the largest angle down, just slightly larger than for Menu.

AvatarAvatar the was worst of the rest for HMD angle down. Below Menu and Sphereby 200 and 100 percent and larger than all other. Below average times breachedfor controller height and second most for controller distance.

Avatar was in the middle for max value for controller height and only worse thanThumbpad and Menu for controller distance for this variable.

DragDrag had the least breaches for controller height and had fewer than Sphere, Avatarand Pull for controller distance. Only Thumbpad had less breached for HMD angledown.

But Drag had the lowest max angle for HMD down by roughly 33 percent. Itsmax value for controller height was the lowest and only Thumbpad and Menu hada lower maximum value for controller distance.

PullOnly Thumbpad and Sphere had more combined breaches for controller height

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than Pull. Pull did have the most breaches for controller distance. For HMDangle, down it was in the middle, both Thumbpad and Drag had less.

Pull had the highest maximum value for controller distance and almost had thegreatest max value for controller height.

4.1.2 Observations

Below are observations from the tests presented and comments from participants.

ThumbpadOne participant noted that very little movements was needed for the Thumbpadmanipulation control. The participants were able to do fine tuning manipulationswith just the thumbpads. While this controls setup didn’t require any movementfrom the user, many of the participants held the controllers at roughly chest height.

MenuA couple of participant stated that the menu was too close to the player. Theyshifted their hand from resting in the lap and only moving the wrist, to angle thewhole arm out 90 degrees to the side. They did this to get a greater distancebetween the hand and menu

The scaling of the movement was only used for big and small movements. Theparticipants tended to push the move buttons several times instead of adjustingtheir effect. Scaling the effect of the rotation buttons was used more. Some evenused the slider to get the cube in the right general rotation, and then the buttonsto make small adjustments.

One participant noted that the sliders on the menu was shaky and hard to beprecise with.

SphereWith the Sphere manipulation the cube stopped moving when the controller re-entered to sphere. Several participants had trouble to stop the cube at the rightmoment, because they were focused on the cube and not the sphere. They didn’tsee the sphere and controller when they tried to merge them. This lead to that theydid several small adjustments while the cube was on top of the plane. It also causedseveral of the participants to tense their hand during the whole manipulation

Almost none of the participants moved the sphere after the warm up period.

One participant stated that they felt they had good precision for the orientationof the cube with the Sphere manipulation.

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AvatarOne participant said that the Avatar control setup was uncomfortable for thewrist. One other commented that they had to reach far with the avatar. Severalparticipants had their hands in their lap while manipulation the avatar.

Sense the Avatar could be scaled up it got in the way for several participants.

DragThe Drag manipulation control was shaking for many of the participants. Theycould quickly get the cube close to the plane, but once there, they struggled to getan exact position which prolonged the time.

PullThe Pull mechanic allowed the user to move the cube with the combined move-ments of the controllers. To move it great distances it had to be moved in severalsteps, moving the controllers back and forth. Some participants did this with smallsteps, keeping the arms relatively close, while others moved the arms as much asthey could each time.

GeneralOne observation for all manipulation controls is that the participants tended to dothe manipulation in steps. First scale, then move and finally rotate for example.And then cycle through them a couple of times before they were satisfied.

From the graphs and observations, it shows that the participants looked down a lotduring the warm up periods. These angles were often greater and more frequentthan during the tasks and occurred for all manipulation controls.

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4.2 RULA

The presented poses below are derived from the data shown above. Each manipu-lation control have two poses, seen in table 5 and 6. Both are based on the databut one is exaggerated.

Table 5: RULA poses

Thumbpad Menu Sphere Avatar Drag PullUpper arm 1 1 3 2 3 3Upper arm adjustment 0 0 0 0 0 0Lower arm 2 1 1 2 1 2Lower arm adjustment 0 0 1 1 1 1Wrist 1 2 3 3 2 1Neck 2 3 2 3 1 2Neck adjustment 0 1 0 0 0 0Trunk 1 1 1 1 1 1Trunk adjustment 0 0 0 0 0 0

Table 6: RULA poses, exaggerated

Thumbpad Menu Sphere Avatar Drag PullUpper arm 2 2 3 3 3 3Upper arm adjustment 1 1 1 1 1 1Lower arm 2 2 2 2 1 2Lower arm adjustment 0 1 1 1 1 1Wrist 2 4 4 4 4 2Neck 2 3 2 3 1 2Neck adjustment 1 1 1 1 1 1Trunk 2 2 2 2 2 2Trunk adjustment 1 1 1 1 1 1

4.2.1 RULA result

The results from the RULA evaluation can be seen in tables 7 and 8. All notexaggerated poses got a final score of 3 or 4. Both scores are within the samecategory, investigate further. 3 is the lower limit and 4 the upper limit for thiscategory. Thumbpad was the only pose with a score of 3. The pose had the upperarms low, no wrist angle and moderate neck angle. All other poses had either thearms raised, greater wrist angle, or both.

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Table 7: RULA final score

Controls Final scoreThumbpad 3Menu 4Sphere 4Avatar 4Drag 4Pull 4

The result for the exaggerated poses varied more than the original poses did. Twoof the poses got the highest score possible (7), the poses were for Menu and Avatar.Both these poses had a high neck angle, the largest wrist angle and the arms wasraised for both. A final score of 7 is in its own category. All other poses got a scoreof 5 or 6 which is in the category below, investigate further and change soon. Theexaggerated poses for Sphere and Drag got a score of 6. They had a large wristangle and the arms raised. The exaggerated poses for Thumbpad and Pull got ascore of 5. They had a low wrist angle and moderate neck angle.

Table 8: RULA final score exaggerated

Controls Final scoreThumbpad 5Menu 7Sphere 6Avatar 7Drag 6Pull 5

4.3 Volumes

With data regarding anthropometrics, comfortable neck angles, HTC Vive’s hard-ware data and the human sight, several volumes can be defined which displayswhere the human body preferably want to interact. These are made with the as-sumption that the user is stationed on a non-rotating chair and that they read textand focus on things which are in the centre of the visual field.

4.3.1 Viewing volumes

If the comfortable and maximum angels for the neck is combined with the prefer-able viewing range and area, hardware limitations for the Vive, a volume can bedefined in which everything the player can focus on is. With an extension of

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Chu:s terminology these are referenced to as the comfortable viewing volume andmaximum viewing volume.

These volumes can be seen in figures 16, 17 and 18. The two viewing volumes areyellow (the comfortable viewing volume) and red (the maximum viewing volume)in the pictures. The black sphere represents the user’s head. As seen in figure 17,the viewing volumes doesn’t extend to the user’s eyes. It starts at 75 cm in frontof the eyes and extends to 3.5 meters in front of the user.

Figure 16: The viewing volumes seen from an angle

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Figure 17: The viewing volumes seen from the side

Figure 18: The viewing volumes seen from the front

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4.3.2 Working volumes

If the recommendations for working space height, posture, percentiles for armlength, elbow height and upper body length is taken into consideration, volumeswhich shows the arms reach can be defined. A comfortable working volume anda maximum working volume. The maximum is how far the arms reach, and therecommended is how far the arms can reach while the upper arm is close to thebody.

These volumes can be seen in figures 19, 20 and 21. The blue objects in the picturesare the comfortable working volume. It origins from the elbow and extends to thefingertips. It has the same height as the elbow and is angled down 90 degrees. Ifthe upper arm is allowed to be angled 30 degrees from the body, as Bjurvald states[20], then the comfortable working area can be moved around 16 cm (depends onthe length of the person’s in question upper arm and lower arm) forward. This isthe case for these models. The maximum working volume are green in the picturesand extends from the shoulders. It has the reach of an outstretched arm. It doesn’textend over the shoulder and is angled 90 degrees down

Figure 19: The working volumes seen from an angle

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Figure 20: The working volumes seen from the side

Figure 21: The working volumes seen from the front

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4.3.3 Working and viewing volumes combined

In the figures below (22, 23), both the volumes for the neck and the arms beencombined into one model.

Figure 22: The viewing and working volumes seen from an angle

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Figure 23: The viewing and working volumes seen from the side

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5 Discussion

The discussion will firstly go though the result of the theses and then the method-ology used in the work.

5.1 Result

The cubes manipulation was greater than the input from the controllers in somecases. A study which researched this found that a higher amplification makes theuser less fatigued [52]. It could also affect the outcome of the RULA evaluation.With a sufficiently low Control/Display ratio the arms wouldn’t have to be raisedas high and don’t have to work out to the sides. The wrist angles could also bekept smaller. All manipulation controls which got a final score of 6 or 7 had thelargest score possible for wrist angle. While to ones that got a 5 only had half thatscore for wrist.

A control setup which used the wrist a lot was Drag. While using Drag the cubewas shaking for all participants. They could quickly get the cube on top of thereference plane, but they had trouble placing it exactly. This resulted in thatthe user had their arm outstretched for longer than necessary. Drag is shakingbecause it places the cube at an extension of the controller. A small movementof the controller is amplified for the cube. Keeping the arm outstretched leads tolactic acid accumulation and that the arm becomes fatigued [9, 19]. One studyshowed that having the arm stretched out can make the user fatigued after 10minutes [1]. Another blamed shoulder discomfort on that the users’ arm had to beextended [46].

Both Sebastian Boring et al. [51] and A. Cockburn et al. [49] brings up that itis less fatiguing to let the wrist and hand move instead of the whole arm. Themanipulation controls which got the highest RULA scores was exaggerated Menuand Avatar. Both had highest score for wrist angle and a high score for neck. ButMenu had a lower score for arm height than some other controls. What contributedits high final score was high wrist and neck angle. While the exaggerated poses forSphere and Drag both had a score of 3 for the upper arm and got a final score of6.

If the wrist is angled more than 15 degrees and angled away from the midpoint,that is 3 more points in the RULA evaluation compared to if the wrist would havebeen in a neutral position. The benefits of having the arm low and still must bebalanced with the downsides of moving the wrist a lot.

Designing a virtual environment that doesn’t require arm and hand movementmight not be enough. Thumbpad reached the limit for controller height with highfrequency. It points to that the participants had their hand higher that necessary.The control setup requires no movement from the arms and the user can rest

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their hands in their lap. Thumbpad had the fewest limits reached for HMD whichsuggests that they didn’t look down on the controllers, which also point to thatthis wasn’t the reason to keep the hands up high.

The test was relatively short so it wasn’t likely that any participant would becomefatigued during the Thumbpad manipulation. It might be that they would lowertheir hands when they start feeling tired. Sebastian Boring et al. observed thisin their test [51]. But the user shouldn’t have to come to that point if it can beavoided. It shows how important it is that the software is used as intended. Otherdata that support this is that Thumbpad compared to Pull had almost the sameamount of violations for controller height. Pull need much movement from botharms.

Juan David Hincapié-Ramos et al. [3] did a study looking at mid-air interactions,and suggests that the area that should be most frequently used is in the oppositelower corner of the active hand. When applying this to a RULA evaluation it maynot give a better result. Working across the body gives an extra score in the RULAsheet. By just adjusting this parameter in the sheets the result can be changed.For both Pull and Avatar the result goes from a 4 to a 3 if the parameter is set to0 form a 1. This is still in the same category but the lower tier. On the other hand,Menu rises from a 4 to a 5 if the parameter is set to 1. This is in a higher category,and the verdict goes from “Investigate further” to “Investigate further and changesoon”.

It is not surprising that Menu had the most violations for looking down as themenu is located down and in front of the user. It also demands a lot of attentionfrom the user. Interacting with the menu only requires wrist movement and thehand can rest in the lap. But Menu had many instances of the hands being highand the max value wasn’t low. Several participants thought the menu was to closeand therefor had their arm in a weird angle.

It has been shown that inexperienced users to VR want to keep the controllerswhere they can see them while using them [46]. This thesis’s results indicate some-thing similar. That the user looks at the controller when they are familiarizingwith them. Not just the physical controller, also when it is used in a new way inthe virtual environment. All manipulations controls had a lot of HMD angle downduring the warm up sessions. This happened probably because the participantswere getting familiar with the controls and therefor looked at the controllers. Hav-ing the controllers represented in the virtual environment is an aid to new user asit gives them a straightforward way to double check the controllers. But in turn itencourages them to look down with a steep angel.

Harrison et al. [47] argues that by placing graphics on the user’s hand, the handcan be placed in a preferable position for the neck. A problem with this in VR isthat the FOV is limited and the resolution is only good at the center in the HMD.This results in that either the neck must bend to much or the hand be placed toohigh, as shown by the volumes.

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Because either the hands or neck must be compromised to get the hands into view,placing graphics on the hands isn’t preferable. But it can be adjusted. Instead ofhaving graphics or interfaces on the hands, they can be placed above or in front ofthem. This leads to that the hands don’t have to be lifted too high and that theneck doesn’t have to bend to much to see it.

A drawback of having graphics or an interface around the hands is that that mighttake focus from what the user wants to do. The Sphere manipulation forced theparticipants to either look at the sphere and controller or at the cube. When theuser wanted to stop a moving cube, they had to get their hand into the sphere.The problem was that the user was looking at the cube and not the hand andsphere. This forced the them to second guess when the sphere and hand wouldcollide. This lead to that they had to do many small adjustments with their armstretched out for longer.

A reason for Pull having a lot of limits reached and high max values for controllerheight could also be because of the interface. The graphics for Pull is displayedon the controllers. So, if the user wanted to see the graphics and the cube at thesame time they were required to raise their hands.

5.2 Method

This chapter firstly presents the reasoning for choosing RULA to evaluate theergonomics. Secondly it discusses the data collecting software.

5.2.1 Method choice

RULA was chosen to evaluate the ergonomics as it has a focus on the upper bodyand high fidelity of the arms and neck. RULA also takes into consideration if aposture is static or repeated often.

One downside to RULA compared to OWAS is that it has less fidelity when it comesto balance. But the test was done sitting down so having many different states ofbalance is irrelevant in the evaluation. In comparison OWAS only considers if one,two or none of the arms are above shoulder height, whereas RULA have severalsteps. OWAS also focuses on heavy lifts, and as the Vive controllers weight 203git wasn’t relevant to consider heavy lifts.

Both RULA and OWAS are objective methods. A reason for deploying one of theseinstead of a subjective, is that the subjective methods rely on the participants toreport their level of fatigue, and the test was relatively short. In one study ([52])which used the Borg CR10 scale had a test for 40 minutes with one type of controllersetup Another [46] tested for 20 minutes. This thesis wouldn’t had been able totest as broadly as it did with 6 manipulation controls if each test required thatmuch time.

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Using the Borg RPE scale would be a neat way to determine the heart rate ofthe participants without any measuring equipment. Having the heart rate for eachmanipulation control could have been a good indication on fatigue. But this wouldrequire longer sessions with the participants for each controller setup to make themfatigued. This is also true if the Borg CP10 scale would have been used.

Another subjective method is NASA TLX. It was not chosen although it is widelyused. One strength of the method is that it allows a task to be studied fromvarious angles and see the effects on a person by different variables. But this isn’tnecessary in this project, and several of the variables isn’t within the scope of thisthesis. For example, temporal demand and frustration level.

5.2.2 Monitoring program

The limit for HMD angle down was reached almost constantly throughout the tests.There are four possible reasons for this. Firstly, the test required the participantto look down. And because the resolution in the HMD is better in the middle, itis better to angle the head instead of just the eyes. The weight of the HMD alsoangles it down slightly. Even if the head is looking straight forward, the HMD isangled down. The limit for the angle down is small (12 degrees). If the HMD isjust angled down a few degrees on its own, it is already close to the limit.

Because the limit was reached with this frequency the data might not be particu-larly relevant. A cube that had to be moved close to the player instead of faraway,could affect the result as well. To combat this the angle of the HMD could bezeroed for every participant. Then during the test, it measures the deviation fromthe original angle.

Very rarely did the limit for looking left or right get breached. The test in itselfdidn’t require the user to look over 30 degrees to the sides. The times that it gotbreached a notable amount of times was for menu and sphere. The menu is widewhich forces the user to look to the side. It is also place close to the user whichdemands a greater angle than if it was further away. The sphere got the breachesfor similar reasons as menu. The sphere is placed close to the user and to the side.If the user wants to look at it, it forces them to twist their neck.

For the two limits that concerns the controllers a margin was used. The controllerhad to be above the elbow plus a set amount or further away from the HMD thanthe forearms length plus a set amount for the program to register. The reason forusing the margin was to only log relevant data. If only the elbow height was usedthen a small angle of the hand could make the controller come above the elbow.Similarly, if the forearm length was only used for distance check, the programwould register a lot. The point it measures from on the controller is in front of thearm then the controller is held.

The test was done sitting down. The reason for this was so that the angles takenfrom the HMD would be the neck turning and not the whole body. With more

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equipment, the trunk could also be monitored. This could be beneficial as the backhas a big part of the RULA evaluation. Another body part which influenced theRULA result was the hands. The orientation of the controllers was not monitored.The steps for the hands in the RULA sheet is quite crude. The steps are: no angle,up to 15 degrees and more than 15 degrees. As these are large steps it could bederived from observations what the wrist angles was for the different manipulationcontrols. By not monitoring the controllers’ orientation, small nuances was lost.For example, if the wrist was twisted or bent from the mid line. To measure thiswith certainty, the users’ arms would also have to be monitored.

5.2.3 Source criticism

The papers that were studied about ergonomics in VR was done on a wide rangeof VR-hardware. Several of the studies was more than decade old which in turnmean that the equipment used is dated. It is likely that they would weigh moreand be less comfortable to use. There might also other issues as lag and limitedgraphics. Which mean that results from these studies might not apply fully whenlooking at today’s hardware.

As the VR is a topical subject today many technical and gaming websites andblogs discuss the subject. An effort was made to exclude these sources when datawas available from academic resources.

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6 Conclusions

This thesis has evaluated six different manipulation controls in virtual reality inregards to ergonomics. Each method displayed how different interactions in VRmay have consequences for the body.

When designing for VR with ergonomics in regard, not just anthropometric datasuch as arm length and elbow height is important. A knowledge of the limitationsfor the VR system is also required. Where to put elements in the virtual environ-ment can be limited by FOV, resolution and viewing distances. The weight of theequipment may affect how demanding the interactions are for the body.

How far from the body and how high the arm is, isn’t enough to evaluate the arm’sposture. The wrist angle can affect the overall posture as well. Moving the armdown but allowing the wrist to bend more can result in a worse posture. And bynot allowing the arm to work out to the side or across the body, the overall posturecan be improved.

The resolution in a HMD forces the user to turn and bend the neck instead ofmoving the eyes. What the user can see by just turning the neck is limited, if itis kept at a comfortable level. If the user is only turning their neck and lookingstraight forward, and the hands are kept at a recommended height, the hands don’tenter the visual field.

6.1 Future research

Future research could address the same issues as this thesis while monitoring morebody parts. The results from this study shows that different body parts can affectthe severity of the overall posture. By monitoring more body parts a higher detailedevaluation can be made. A greater nuance between the different interaction couldbe found if, for example, the trunk and wrists were monitored. This could be donewith motion capture equipment. It would also allow for movements to be analysedinstead of just static postures.

As the test for each manipulation control was short, the user may not have gotaccustom to the controls. If the users are allowed longer session, they might changetheir posture to something that combats fatigue. Being able to see when and howthe postures change may show how the user adapts to the virtual environment.

The compromise between the hands and neck discussed in the thesis poses a prob-lem when designing virtual environments. It would be interesting to balance thecomfort of the neck against the comfort of the arms, to find the best overall solu-tion. Taking into account how much the body parts deviate and how often theydo so.

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