journal of orthopaedic & sports physical therapy | volume 42 | number 5 | may 2012 | 437

[ research report ]

Stationary running, which consists of running without changing location, is an exercise frequently used in aerobic gymnastics classes, track and field, and other sports training sessions, as well as rehabilitation programs. Its

use is based on several objectives, such as physical conditioning and

coordination training, mainly when a sufficiently large area for running is not available. In addition, this exercise has

also frequently been part of aquatic pro-grams, designed for athletes and nonath-letes, with the intention of providing a

reduction in the load required to support the body against gravity.

Because of the common use of stationary running in water and on dry land, this exercise has

recently been investigated in the litera-ture.1,2,6 However, these studies have only focused on physiological parameters such as heart rate, rate of perceived exertion, and oxygen uptake. Therefore, there is a lack of biomechanical data regarding the execution of this exercise. While the literature provides extensive data on the kinematic and kinetic variables related to running,10,14,18,19,25,30,50 minimal data exist on stationary running.13

The analysis of ground reaction forces (GRFs) during exercise is important to quantify the magnitude of forces sus-tained by body structures during move-ments.23 GRFs can be influenced by several factors, such as the environment in which the exercise is executed (eg, on land or in water),4,12 movement speed,19,29 and the sex of the individual performing the exercise.7,20

On dry land, in addition to studies in-vestigating running, several other studies have described the GRFs during gait,49 jogging,19 jumping,24 and stair climb-ing and descent.34 For aquatic exercises, GRFs have been described for gait4,26,36 and, more recently, running14 and jump-

TT STUDY DESIGN: Controlled laboratory study.

TT OBJECTIVES: To analyze the vertical and an-teroposterior components of the ground reaction force during stationary running performed in water and on dry land, focusing on the effect of gender, level of immersion, and cadence.

TT BACKGROUND: Stationary running, as a fundamental component of aquatic rehabilitation and training protocols, is little explored in the literature with regard to biomechanical variables, which makes it difficult to determine and control the mechanical load acting on the individuals.

TT METHODS: Twenty-two subjects performed 1 minute of stationary running on land, immersed to the hip, and immersed to the chest at 3 different cadences: 90 steps per minute, 110 steps per minute, and 130 steps per minute. Force data were acquired with a force plate, and the variables were vertical peak (Fy), loading rate (LR), anterior peak (Fx anterior), and posterior peak (Fx posterior). Data were normalized to subjects’ body weight (BW) and analyzed using repeated-measures analysis of variance.

TT RESULTS: Fy ranged from 0.98 to 2.11 BW, LR ranged from 5.38 to 11.52 BW/s, Fx anterior ranged from 0.07 to 0.14 BW, and Fx posterior ranged from 0.06 to 0.09 BW. The gender factor had no effect on the variables analyzed. A significant interac-tion between level of immersion and cadence was observed for Fy, Fx anterior, and Fx posterior. On dry land, Fy increased with increasing cadence, whereas in water this effect was seen only between 90 steps per minute and the 2 higher cadences. The higher the level of immersion, the lower the magnitude of Fy. LR was reduced under both water conditions and increased with increasing cadence, regardless of the level of immersion.

TT CONCLUSION: Ground reaction forces during stationary running are similar between genders. Fy and LR are lower in water, though the values are increased at higher cadences. J Orthop Sports Phys Ther 2012;42(5):437-443, Epub 8 March 2012. doi:10.2519/jospt.2012.3572

TT KEY WORDS: aquatic exercises, biomechanics, hydrotherapy, kinetics

1Physical Therapist, University of the State of Santa Catarina, Health and Sports Science Centre, Aquatic Biomechanics Research Laboratory, Florianópolis, SC, Brazil. 2Physical Educator, University of the State of Santa Catarina, Health and Sports Science Centre, Aquatic Biomechanics Research Laboratory, Florianópolis, SC, Brazil. 3Senior Lecturer, University of Brighton, School of Health Professions, Eastbourne, UK. 4Associate Professor, University of the State of Santa Catarina, Health and Sports Science Centre, Aquatic Biomechanics Research Laboratory, Florianópolis, SC, Brazil. This study was approved by the Ethical Committee for Research on Humans of the Santa Catarina State University, Florianópolis, SC, Brazil. Address correspondence to Dr Heiliane de Brito Fontana, Rua Pascoal Simone, 358 - Coqueiros, Florianópolis - SC, CEP 88080-350 Brazil. E-mail: lilly_bfontana@hotmail.com

HEILIANE DE BRITO FONTANA, PT, MSc1 • ALESSANDRO HAUPENTHAL, PT, MSc1 • CAROLINE RUSCHEL, PE, MSc2

MARCEL HUBERT, PE, MSc2 • COLETTE RIDEHALGH, PT, MSc, MMACP3 • HELIO ROESLER, PhD4

Effect of Gender, Cadence, and Water Immersion on Ground Reaction Forces

During Stationary Running

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[ research report ]ing.5,46 However, to our knowledge, the GRFs during stationary running in water or on dry land have not previously been described.

Despite buoyancy, stationary running in water still involves contact forces. Body tissues are considered anisotropic and, therefore, respond differently to dif-ferent load directions. For this reason, it is necessary to know both the magnitude and direction of the applied forces. The lower- and upper-limb movements dur-ing stationary running occur primarily in the sagittal plane and, therefore, mostly require vertical and anteriorly and poste-riorly directed GRFs. Although we could assume that the magnitude of the vertical GRFs in water would be lower than that observed during overground running, in some cases it could be excessive and even harmful, depending on the condition of the individual.14 Therefore, quantifica-tion of GRFs based on level of immer-sion and cadence may be helpful to guide rehabilitation.

Given the growing use of water exer-cises,8,21,22,33,39-41,45 as well as the limited literature regarding GRFs acting on the body during stationary running, the pres-ent study aims to determine the effects of gender, water immersion, and cadence on the vertical and anteriorly and posteriorly directed components of GRFs during sta-tionary running.

METHODS

Prior  to  data  acquisition,  par-ticipation of students from the Physical Education program at the

University of the State of Santa Cata-rina, who volunteered in response to an advertisement, was determined based on the following criteria: percentage of body fat (between 12% and 20% for men and 20% and 25% for women32); being recreational athletes; being active in sports such as swimming, soccer, vol-leyball, or track and field; and being fa-miliar with aquatic exercises and able to swim. Subjects were excluded if they had suffered any injury or undergone any

surgery in the previous 2 years. Twen-ty-two healthy subjects (11 male and 11 female) met the inclusion criteria and participated in this study. The protocol for this study was approved by the Ethi-cal Committee for Research on Humans of the University of the State of Santa Catarina, and written, informed consent was obtained from all subjects. Mean SD age, height, and mass for the male subjects were 24.0 3.0 years, 1.80 0.05 m, and 74.6 6.8 kg, respectively. For the female subjects, mean SD age, height, and body mass were 23.0 2.5 years, 1.67 0.05 m, and 56.3 3.8 kg, respectively.

Data for the vertical and the antero-posterior GRFs were collected with a wa-terproof force plate covered by a nonslip material (dimensions, 500 mm × 500 mm × 200 mm; sensitivity, 2 N; error lower than 1%), which was developed by Roesler35 and validated by Roesler and Tamagna.37 The data acquisition system also included a signal conditioner and A/D converter (ADS2000 IP; Lynx Tec-nologia Eletrônica, São Paulo, Brazil), as well as signal analysis and editing soft-ware (AqDados 7.02; Lynx Tecnologia Eletrônica, São Paulo, Brazil).

Each subject took part in 2 days of data collection. On the first day, an-thropometric data and force data in an aquatic environment were acquired. Force data on land were acquired on the second day. The sessions were held in the Aquatic Biomechanics Research Laboratory of the University of the State of Santa Catarina and at the swimming pool of the Health and Sports Science Centre, University of the State of Santa Catarina.

Anthropometric data were acquired as follows: (a) body mass of the subjects using an electronic scale (model MEA-08128; Plenna Especialidades LTDA, São Paulo, Brazil; scale of 0.1 kg), (b) height of the subjects using a stadiometer (Sanny American Medical do Brasil LTDA, São Bernardo do Campo, Brazil; scale of 0.01 m), and (c) subjects’ cutaneous folds us-ing a scientific caliper (CESCORF Equi-

pamentos Antropométricos LTDA, Porto Alegre, Brazil; scale of 0.1 mm). Percent-age of body fat was determined through the calculation of subjects’ body density.44 For the male subjects, body density was calculated via a regression equation using the sum of the thoracic, abdominal, and thigh skin folds.16 For women, the regres-sion equation used the sum of the triceps, supra iliac, and thigh skin folds.17

For the GRF data collection, trials were considered valid when the subjects touched the force platform with only 1 foot at a time, reflective of a flight phase (with no double-support phase), without looking downward, and without chang-ing cadence. The cadence was controlled by a metronome and the participants were instructed to step on the force plate according to the metronome beats. The cadence was verified during the data analysis through fast Fourier transform, and a variation of less than 2 steps per minute in the set cadences was required to accept the data.

After the anthropometrical measure-ments, the subjects were asked to enter the pool. The stationary running exercise was demonstrated, and subjects were giv-en detailed instructions on safety issues while in the pool. To familiarize them-selves with the equipment, subjects were given 5 minutes of practice and were then instructed to perform the stationary run-ning exercise for 1 minute at 3 different cadences (90 steps per minute, 110 steps per minute, and 130 steps per minute) and at 2 levels of immersion. The 2 levels chosen were hip level, which correspond-ed to the subject’s iliac crest, and chest level, which corresponded to the subject’s xiphoid process.

The order of the immersion levels and cadences was randomly allocated by drawing lots, and the participants had an interval of 2 minutes between each con-dition. The chosen cadences were based on a previous pilot study in which mean values for a slow, medium, and fast rate were found, whereas the choice of levels of immersion was made by the research-ers, according to anatomical points that

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journal of orthopaedic & sports physical therapy | volume 42 | number 5 | may 2012 | 439

could be easily identified and are widely used by professionals who prescribe aquatic exercises.

On the second day, the same force plate was used to acquire the force data on land. Subjects were also given 5 minutes of practice and instructed to perform the stationary running exer-cise for 1 minute at 90 steps per min-ute, 110 steps per minute, and 130 steps per minute. The order of cadences was randomized.

All GRF data were exported and ana-lyzed through a processing routine cre-ated with Scilab 4.1.2 software (Institut National de Recherche en Informatique et en Automatique, Rocquencourt, France), which consisted of the following phases:1. Application of calibration coefficient

and filters (low-pass Butterworth 20 Hz, determined from analysis of the spectral density of the signal strength).

2. Normalization based on the subject’s body weight as measured outside the water.

3. Selection of individual steps, for a total of 30 steps per subject.

4. Verification of the peak value for the GRF in the vertical (Fy), anterior (Fx anterior), and posterior (Fx posterior) directions. For this study, the peak value was defined as the maximum positive (Fy and Fx anterior) and neg-ative (Fx posterior) values normalized by body weight, occurring at any time for each step on the platform.

5. Calculation of loading rate (LR). The LR was calculated from the linear slope of the vertical component of the GRF, from initial contact to the onset of maximum force.

6. Average calculation of 30 steps per subject for Fy, LR, Fx anterior, and Fx posterior.An additional normalization of Fy

peak was performed to determine the percentage of load reduction in compari-son to the values obtained during station-ary running on dry land. Fy data were divided by the Fy values achieved on dry land at each of the cadences studied, and

the result was multiplied by 100 to obtain percentage values.

SPSS Version 17.0 software (SPSS Inc, Chicago, IL) was used to analyze

the data. Means and standard deviations were calculated for Fy, Fx posterior, Fx anterior, and LR for each running condi-tion. Four 3-factor mixed-model analyses

TABLE 1Ground Reaction Forces During Stationary Running for Men and Women Immersed to

Chest and Hip Level and on Dry Land*

Abbreviations: Fx anterior, anterior peak; Fx posterior, posterior peak; Fy, vertical peak; LR, loading rate.*Data are mean SD normalized to the subject’s body weight, except for LR, which is in body weight per second. Data are from a sample of 11 males and 11 females. No statistically significant differences were found between genders.

Cadence

Variable Level 90 Steps/min 110 Steps/min 130 Steps/min

Fy Chest

Men 0.93 0.23 1.07 0.23 1.16 0.19

Women 1.02 0.21 1.11 0.21 1.10 0.24

Hip

Men 1.14 0.26 1.34 0.31 1.40 0.40

Women 1.10 0.13 1.27 0.13 1.31 0.18

Land

Men 1.80 0.21 1.89 0.37 2.12 0.35

Women 1.83 0.14 1.95 0.24 2.08 0.28

LR Chest

Men 5.06 2.26 7.50 3.74 9.42 3.17

Women 5.93 1.60 7.86 1.85 8.91 2.05

Hip

Men 5.38 1.73 7.72 2.72 9.84 2.60

Women 5.37 1.50 8.57 1.70 10.41 2.04

Land

Men 7.88 3.51 9.60 3.49 11.70 4.12

Women 9.05 2.42 10.29 2.96 10.84 3.69

Fx anterior Chest

Men 0.08 0.03 0.06 0.01 0.06 0.01

Women 0.12 0.04 0.09 0.05 0.08 0.04

Hip

Men 0.10 0.02 0.12 0.03 0.11 0.04

Women 0.12 0.03 0.15 0.06 0.13 0.04

Land

Men 0.10 0.03 0.11 0.04 0.12 0.04

Women 0.11 0.03 0.11 0.03 0.10 0.02

Fx posterior Chest

Men 0.06 0.03 0.07 0.04 0.07 0.02

Women 0.07 0.03 0.08 0.02 0.07 0.02

Hip

Men 0.06 0.02 0.07 0.03 0.07 0.02

Women 0.08 0.02 0.10 0.03 0.08 0.03

Land

Men 0.07 0.02 0.06 0.01 0.07 0.02

Women 0.07 0.02 0.07 0.01 0.08 0.02

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[ research report ]of variance (ANOVAs) were conducted to analyze the effect of gender, level of immersion, and cadence on Fy, LR, Fx anterior, and Fx posterior, and also to verify the interaction between factors. The within-subjects factors were im-mersion with 3 levels (hip level, chest level, and dry land) and cadence with 3 levels (90 steps per minute, 110 steps per minute, and 130 steps per minute). The between-subjects factor was gender with 2 levels (male and female). An alpha level of .05 was used for all statistical tests. Ef-fect size of gender was estimated through partial eta-squared (η2).

Based on the above model, because there was no significant 3-way or 2-way interaction that included gender and no significant main effect of gender, the data for both genders were pooled together and the data were analyzed based on 4 separate, 2-factor (3 levels of immer-sion by 3 cadences), repeated-measures ANOVAs. The Bonferroni test was used for multiple comparisons.

RESULTS

The  3-factor  mixed  ANOVA  did not show any statistically signifi-cant differences between genders

for Fy (P = .883, partial η2 = 0.001), LR (P = .624, partial η2 = 0.008), Fx ante-rior (P = .074, partial η2 = 0.160), and Fx posterior (P = .355, partial η2 = 0.038). There was no statistically significant 3- or 2-way interaction that included the factor gender. P values and the effect sizes for each interaction that included gender (gender by level by cadence; gen-der by level; gender by cadence) were Fy (P = .465, partial η2 = 0.043; P = .732, partial η2 = 0.015; P = .559, partial η2 = 0.029, respectively), LR (P = .228, partial η2 = 0.067; P = .976, partial η2 = 0.001; P = .249, partial η2 = 0.067, re-spectively), Fx anterior (P = .165, partial η2 = 0.077; P = .198, partial η2 = 0.078; P = .075, partial η2 = 0.122, respectively), and Fx posterior (P = .634, partial η2 = 0.031; P = .534, partial η2 = 0.031; P = .630, partial η2 = 0.023, respectively).

Descriptive data for Fy, LR, Fx anterior, and Fx posterior for each running condi-tion are shown separately for men and women in TABLE 1.

After pooling the data of both gen-ders together, FIGURE 1, based on the least-squares means standard error of mean from the 2-way ANOVAs, presents the effect of immersion level and cadence for each GRF variable. Descriptive sta-tistics for the pooled data are provided in TABLE 2.

A significant interaction between cadence and level of immersion was ob-served for Fy (P = .041), indicating that the effect of cadence was different based on the running environment. When stationary running on land, Fy was sig-nificantly progressively higher as the ca-dence increased; in water, no difference was observed between 110 steps per min-ute and 130 steps per minute. In addi-tion, there was a significant progressive reduction in Fy from running on land to running in hip-deep water to running in chest-deep water at all 3 running ca-

dences. From dry land to chest immer-sion, the peak force nearly decreased by half (FIGURE 2).

No significant interaction between level of immersion and cadence was ob-served (P = .061) for LR, but there were significant main effects for both cadence and immersion level. The main effect for immersion level indicated that LR is higher when running on land compared to both immersion levels, and that there was no difference between water immer-sion levels. The main effect for cadence indicated a significant increase in LR for each increment in cadence.

A significant interaction between ca-dence and level of immersion was ob-served for Fx posterior (P<.001) and Fx anterior (P = .028), details of which are provided in TABLE 2. Fx anterior varied from 0.07 to 0.14 body weight (BW), and Fx posterior varied from 0.06 to 0.09 BW. Despite the statistically significant differences, changes in immersion and cadence had relatively minor effects on Fx anterior and Fx posterior.

4.5

90 steps/min 110 steps/min 130 steps/min

5.5

6.5

7.5

8.5

9.5

10.5

11.5

12.5

LR, BW/s

0.04

90 steps/min 110 steps/min 130 steps/min

0.05

0.06

0.07

0.08

0.09

0.10

Fx Posterior, BW*

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

90 steps/min 110 steps/min 130 steps/min

Fy, BW*

0.06

90 steps/min 110 steps/min 130 steps/min

0.08

0.10

0.12

0.14

0.16

Fx Anterior, BW*

ChestHipDry land

FIGURE 1. Effect of cadence and immersion level on ground reaction forces during stationary running. Least-squares mean standard error of mean of Fy, LR, Fx anterior, and Fx posterior. *Significant interaction between factors (P<.05). Abbreviations: BW, body weight; Fx anterior, anterior peak; Fx posterior, posterior peak; Fy, vertical peak; LR, loading rate.

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journal of orthopaedic & sports physical therapy | volume 42 | number 5 | may 2012 | 441

DISCUSSION

Running in water has become a popular mode of aerobic training.1,2,6 It reduces the risk of orthopaedic

trauma often experienced with on-land running, making it accessible to injured athletes.14 Because the effects of detrain-ing can occur within 2 to 4 weeks after the cessation of activity, it is very impor-tant for an injured athlete to perform a sport-specific exercise as early as pos-sible.15,27,48 Stationary running has been indicated as a useful exercise to prevent detraining or to maintain aerobic capac-ity in athletes.6

Because rehabilitation should be de-signed to maximize musculoskeletal function with the least amount of risk, water exercise is a potentially useful approach when partial weight bearing is needed.14,33 However, to achieve suc-

cess and establish a progressive load-ing approach with minimum risk, the practitioner must have knowledge of the loads applied to the body during water exercise. The results of this study show that cadence and immersion level sig-nificantly affect both peak vertical GRF and LR; therefore, these factors should be considered when prescribing station-ary running.

Although a greater reduction in weight bearing is demonstrated when women stand still in water,42 no significant differ-ence was noted between genders in this study. While the lack of significant differ-ences could be due to the small number of subjects, the small effect sizes indicate that men and women who are within the percentage body fat of those tested ex-perience similar mechanical load when performing stationary running.

The buoyancy force, which is equal to

the weight of the fluid displaced by the body, is responsible for the main advan-tage of exercising in water.9 For this rea-son, adjusting the depth of immersion has been described as an effective way of con-trolling loads acting on body structures.14 Compared to dry land, the results of this study showed that peak vertical force was reduced by approximately 45% when the subjects were immersed to chest level and by approximately 35% when immersed to hip level (FIGURE 2). The physiological responses, such as rating of perceived ef-fort, heart rate, and peak oxygen uptake, are also higher during stationary running on dry land compared to hip- and chest-level immersion.2,3

During rehabilitation of an orthopae-dic injury such as ankle sprains, lower-limb fractures, and osteoarthritis,21,22,33,47 it is commonly required to control weight bearing when initiating activities with the patient. To ascertain that stationary running will be safe for the patient, the confidence interval must be considered. Accordingly, our data indicate that 95% of individuals who match the character-istics of our subjects can perform sta-tionary running in water at any of the 3 cadences analyzed with a load of less than 2 times BW.

The greater the LR, the faster the body structures must adapt to a certain unit of force. Individuals exposed to greater force had a shorter time to adapt to this force as cadence was increased. In addi-tion, as expected, higher LRs were found on dry land. When running on land at 3 m/s, compared to stationary running on land, similar vertical peak forces are measured (2.10 BW versus 1.84 to 2.11 BW, respectively).19 In contrast, the LR during running at 3 m/s on land (16.00 to 16.90 BW/s)19 is higher than what we measured in this study for stationary run-ning on land. Therefore, stationary run-ning results in less abrupt force during foot contact. This may be caused by the fact that running is characterized by rear-foot strikes at speeds less than 5 m/s,19 whereas stationary running is character-ized by forefoot strikes.

TABLE 2Ground Reaction Forces During

Stationary Running Immersed to Chest and Hip Level and on Dry Land*

Abbreviations: Fx anterior, anterior peak; Fx posterior, posterior peak; Fy, vertical peak; LR, loading rate.*Data are mean SD normalized to the subject’s body weight, except for LR, which is in body weight per second (BW/s). Data are from a total sample of 22 subjects. No statistically significant interaction between factors was found for LR. Lowercase letters (a,b,c) indicate multiple Bonferroni comparisons between cadences. Uppercase letters (A,B,C) indicate multiple Bonferroni comparisons between levels of immersion. Identical letters (aA) mean nonstatistical difference (P>.05).

Cadence

Variable/Level 90 Steps/min 110 Steps/min 130 Steps/min

Fy

Chest 0.98 0.22aA 1.09 0.21bA 1.12 0.21bA

Hip 1.12 0.20aB 1.29 0.23bB 1.34 0.29bB

Land 1.80 0.17aC 1.94 0.30bC 2.11 0.30cC

LR

Chest 5.38 1.96aA 7.70 2.84bA 9.15 2.59cA

Hip 5.61 1.58aA 8.17 2.23bA 10.14 2.29cA

Land 8.76 2.99aB 9.99 3.14bB 11.52 3.80cB

Fx anterior

Chest 0.10 0.04aA 0.09 0.04abA 0.07 0.04bA

Hip 0.11 0.03aA 0.14 0.06bB 0.12 0.04abB

Land 0.11 0.03aA 0.11 0.03aAB 0.11 0.04aB

Fx posterior

Chest 0.06 0.03aA 0.07 0.03aAB 0.07 0.03aA

Hip 0.07 0.02aA 0.09 0.03bA 0.07 0.03abA

Land 0.06 0.01aA 0.06 0.01aB 0.07 0.02aA

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[ research report ]

REFERENCES

1. Alberton CL, Antunes AH, Pinto SS, et al. Corre-lation between rating of perceived exertion and physiological variables during the execution of stationary running in water at different cadenc-es. J Strength Cond Res. 2011;25:155-162. http://dx.doi.org/10.1519/JSC.0b013e3181bde2b5

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Regarding the anteroposterior force, the values described in the literature range from 0.15 to 0.20 BW for walking and from 0.40 to 0.50 BW for running on dry land.11,28,38 When walking immersed to a depth of 1.3 m, this component varies from 0.08 to 0.20 BW,36 whereas running at a self-selected speed produce vertical forces of 0.26 BW when immersed to chest level and 0.31 BW when immersed to hip level.14 When GRFs during for-ward running in water14 are compared to the ones during forward running on land,11,19,28,38 it seems that the anteroposte-rior component in water is similar to the one on dry land, when the comparison is made within similar speeds. This is likely due to the dragging forces, which oppose the anteroposterior displacement of the body when running in water.9 Therefore, having an individual run in the water environment does not reduce the antero-posterior forces. Exercises with horizon-tal displacement should be prescribed cautiously to patients who have an injury

of an anatomical structure that is vulner-able to shear stress (for example, those with a recent anterior cruciate ligament rupture or reconstruction surgery).31,43 Thus, stationary running may be an al-ternative when control of this compo-nent is necessary. Because there was no effect or a very low effect of immersion found in the anteroposterior component, cases that only require control of shear stresses do not need to be transferred to the aquatic environment to execute the stationary running exercise. The benefits of water stationary running in these cases are less important.

CONCLUSION

This study  indicates that verti-cal GRFs are progressively sig-nificantly reduced by running in

hip- and chest-deep water as compared to running on dry land. LR is lower when running in hip- and chest-deep water, but there was no difference between the

2 levels of immersion. Overall, increas-ing running cadence increases both the vertical GRF and LRs both on land and in water. No differences in loading rates and GRF were found between males and females for any of the conditions. t

KEYPOINTSFINDINGS: Vertical GRF and LRs are significantly reduced by running in hip- and chest-deep water as compared to running on dry land. Overall, increas-ing running cadence increases both the vertical GRF and LRs both on land and in water.IMPLICATIONS: Partial body immersion is a possible option to reduce GRF and LRs on the structures of the lower extremi-ties during running.CAUTION: The values reported in this study are for healthy individuals within normal ranges of body fat.

ACKNOWLEDGEMENTS: We greatly acknowledge the members of the Aquatic Biomechanics Re-search Laboratory, the CAPES Scholarship Programme – Brazil, and Professor Adriano Ferreti Borgatto.

100%

90 steps/min

Dry Land ChestHip

110 steps/min 130 steps/min

100% 100%

62%66% 64%

53%56%54%

FIGURE2.Peak vertical ground reaction forces during stationary running at 2 water immersion levels as a percentage of the peak vertical ground reaction forces during stationary running on dry land for the same cadence.

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