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Effect of Lumbopelvic Control on LandingMechanics and Lower Extremity Muscles’ Activitiesin Female Professional Athletes: Implications forInjury PreventionPari Fadaei Dehcheshmeh 

Razi UniversityFarzaneh Gandomi  ( gandomi777@gmail.com )

Razi UniversityNicola Maffulli 

Baronissi SA

Research Article

Keywords: Lumbopelvic Control, Landing Mechanics, Lower Limb Injury, Jump-landing

Posted Date: March 9th, 2021

DOI: https://doi.org/10.21203/rs.3.rs-250805/v1

License: This work is licensed under a Creative Commons Attribution 4.0 International License.  Read Full License

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AbstractBackground: Lumbopelvic control has recently been associated with function, kinesiology, and limbloading. However, poor lumbopelvic control has not been studied as a risk factor for lower limb injury insports with frequent jump landings. The present study aimed to investigate the effects of lumbopelviccontrol on landing mechanics and lower limb muscle activity in professional athletes with frequentlanding.

Methods: This study was conducted on 34 professional female athletes aged 18.29±3.29 years with themean height and weight of 173.5±7.23 centimeters and 66.79±13.37 kilograms, respectively. Thelumbopelvic control of the subjects was evaluated using the knee lift abdominal test, bent knee fall-out,active straight leg raising, and PRONE test by the pressure biofeedback unit. Based on the test results, theparticipants were equally divided into two groups of with and without lumbopelvic control (n=17).Landing mechanics were evaluated by an expert blinded to the procedures using the landing error scoringsystem (LESS) and two-dimensional video analysis. In addition, electrical muscle activity in single-leggedstanding skills was assessed via surface electromyography.

Results: The results of independent samples t-test indicated signi�cant differences between the groupswith and without lumbopelvic control in terms of the LESS test scores (P=0.0001), lateral trunk �exion(P=0.0001), knee valgus (P=0.0001), knee �exion (P=0.001), trunk �exion (P=0.01), and gluteus mediusmuscle activity (P=0.03). However, no signi�cant differences were observed in the activity of the rectusfemoris and semitendinosus muscles, and ankle dorsi�exion (P>0.05).

Conclusions: Poor lumbopelvic control affects the kinematics and electrical activity of the lower limbmuscles and may be a risk factor for lower limb injuries, especially knee injury.

1. BackgroundThe proper recognition of risk factors and injury mechanisms is essential to the successful prevention ofinjuries [1]. Injuries of the lower limbs (especially the knees) are common in athletes with long termconsequences, such as premature osteoarthritis and poor performance [2]. Frequent jumps and landingsimpose extremely high loads on the lower limbs is in sports such as basketball, volleyball, and handball[3].

The lower limbs account for approximately 60% of all the injuries in these sports [4]: 45-86% of acuteknee and ankle injuries in basketball and volleyball [5] and 70% of anterior cruciate ligament (ACL)ruptures in handball players [6] occur after a landing. The most important risk factors for these injuriesinclude excessive knee valgus, lateral movements of the trunk, and poor pelvic stability [3, 7]. TheNational Institute of Sports Rehabilitation has recommended strength exercises, stabilization, and controlof the lumbo-pelvic-hip complex in injury prevention programs [8]. Furthermore, core stability in lower limbfunction has been reported to be effective in this regard, with evidence suggesting that weakness in thisarea could predict the occurrence of lower limb injuries [9].

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Lumbopelvic control is a risk factor for kinematic disruptions and upper limb injuries [10]. Lumbopelviccontrol is de�ned as the ability to move or stabilize the lumbopelvic region in response to internal orexternal perturbation [10]. Lumbopelvic control depends on the integrity of passive structures andappropriate dynamic neuromuscular control [11]. Although passive structures are partially responsible forthe stability of this area, lumbopelvic control is responsible for muscular structures and neuromuscularcontrol [12].

To date, only the isometric strength of the trunk and hip muscles has been evaluated in studies on theeffects of core stability on the occurrence of lower extremities overuse injuries [9, 13]. In addition to thestrength and endurance of the lumbopelvic-hip complex, optimal neuromuscular control is essential tothe prevention of uncontrolled and compensatory movements [8]. Therefore, the poor neuromuscularcontrol of the lumbopelvic-hip complex, which leads to trunk muscle imbalance, synergist dominance,and compensatory movements, is an important risk factor for lower extremity injuries in athletes. Thestability of any system is the ability to limit displacements and maintain structural integrity [12]. On theother hand, poor lumbopelvic control may affect the muscle activity of the gluteus medius, rectusfemoris, and hamstrings, as they insert or originate on the pelvis, thereby playing a role in knee and lowerlimb injuries [3, 14]. Therefore, it is essential to evaluate the activity of these muscles while standing onone leg.

Previous �ndings have suggested an association between lumbopelvic-hip complex dysfunction andlower limb kinematics [15, 16]. For instance, athletes with weak core stability experience trunkdisplacement more frequently after receiving a perturbation and are more prone to ACL tears [17].Furthermore, there is a link between weak core stability and lower limb injuries [1]. Although the effects ofcore stability on the incidence of lower limb injuries has been studied [12], core stability assessmentshave only been focused on static and one-dimensional lumbopelvic stability while lumbopelvic controlassesses pelvic deviation from the neutral position [18].

In the present investigation, multidimensional lumbopelvic movements were evaluated using dynamictests. Despite the high prevalence of lower limb injuries (especially knee injuries) among athletes withfrequent landings, the main causes of these injuries remain unknown, and no studies have investigatedthe effects of weak lumbopelvic control on the landing mechanics of professional athletes.

The present study aimed to address the following hypotheses:

1) Landing mechanics differ between athletes with and without lumbopelvic control.

2) The activity of the muscles acting on the knee differs between athletes with and without lumbopelviccontrol.

2. Methods

2.1. Participants

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A total of thirty-four female professional basketball, volleyball, and handball players (mean age: 18.29 ± 3.29 years; mean height: 173.5 ± 7.23 centimetres; mean body mass: 66.79 ± 13.37 kilograms) playing inthe Iranian Pro League and Second Division volunteered to participate in the study.

The objectives and procedures were explained to the participants, and written informed consent wasobtained in accordance with the Declaration of Helsinki.The research protocol was approved by the Ethics Committee of Razi University of Iran (code:IR.RAZI.REC.1399.007).The study was performed during September 10-November 6, 2020 at Razi University Sports RehabilitationLaboratory.

The exclusion criteria of the study were the age of less than 17 years or more than 25 years, history oflower back injury or severe lower extremity injuries affecting the normal lower extremity function of theathletes, and neuromuscular disorders (Fig. 1). Since the present study was performed during the COVID-19 pandemic, the subjects were initially referred to the university health centre and excluded if diagnosedwith abnormal symptoms, such as high body temperature (> 37) or hypoxia (< 93%). After each subjectleft the laboratory, the environment was completely disinfected with 70% alcohol.

2.2. ProceduresA case-control design was used to assess the differences in the test results between the athletes with andwithout lumbopelvic control. Data were collected on the age, weight, height, dominant lower limb, numberof the years in high-performance sports, and duration of weekly training (hour). Lumbopelvic control wasevaluated using the knee lift abdominal test (KLAT), bent knee fall-out (BKFO), active straight leg raising(ASLR), and PRONE test by the pressure biofeedback unit (PBU) (Stabilizer®, Chattanooga Group Inc.,Hixson, TN, USA). In addition, the landing error scoring system (LESS) and ImageJ software were used toassess landing mechanics. Finally, wireless electromyography (EMG) (Noraxon, Scottsdale, AZ 85260)was recorded based on the activity of the gluteus medius (GM), rectus femoris (RF), and semitendinosus(ST). To prevent bias, lumbopelvic control diagnostic tests were performed at the end of the evaluations.

1. Lumbopelvic Control Tests

For the KLAT, the subjects were in a crook lying position, and the pressure biofeedback unit (PBU)was placed horizontally under the spine of the participants, with the lower edge at the level of theposterior superior iliac spines (PSIS); the basal pressure of the PBU was adjusted to 40 mmHg. Theparticipants were asked to lift one foot off the examination table until reaching the hip and knee�exion of 90° and hold for 4–6 seconds. Following that, the maximal pressure deviation wasrecorded and used for further analysis (Fig. 2-A).

2. For the BKFO test, the subjects were supine position, and the PBU was placed vertically under thelumbar spine with the lower edge two centimeters caudal of the PSIS on the contralateral side of the�exed knee. In addition, a folded towel was placed near the PBU to keep both sides of the lumbarspine at the same height. The basal pressure of the PBU was adjusted to 40 mmHg. Afterwards, one

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hip was �exed, and the knee was also �exed to 120°, with the foot resting on the surface of theexamination couoch. The participants were asked to slowly bend their hip to approximately 45° ofthe abduction/lateral rotation while keeping their foot supported beside their straight knee and returnto the starting position. The maximal pressure deviation was recorded and used for further analysis(Fig. 2-B).

3. The ASLR was also executed in the supine position, and the PBU placed horizontally under thelumbar spine of the participants, with the lower edge at the level of the PSIS; the calf of PBU wasadjusted to 40 mmHg. The participants lifted one extended leg 20 centimeters above theexamination bed and held it for 20 seconds. The maximal pressure deviation was recorded and usedfor further analysis (Fig. 2-C).

4. In the PRONE test, the participants were positioned prone on the examination table. The PBU wasplaced between the anterior superior iliac spine and navel and in�ated to 70 mmHg. Afterwards, thesubjects were asked to breathe deeply using their abdominal wall. After the completion of twonormal breaths, the in�atable bag was readjusted to 70 mmHg. The subjects were requested toperform three contractions with the following verbal command: “Draw in your abdomen withoutmoving your lumbar spine or pelvis and hold the position until you are told otherwise.” Usingpalpation, the examiner determined whether the participants were moving their spine/pelvis over 10seconds (Fig. 2-D). Pressure changes of equal to or lower than 8 mmHg (up or down) were recordedas successful completion [11, 19, 20].

2.4. Landing MechanicsIn this study, jump-landing tasks were simultaneously recorded by two standard cameras (frontal-sagittalplane views; model: Canon Eos 80D EFS 18-135mm f/3.5–5.6 IS USM Kit Digital Camera). The markerswere placed on the anterior superior iliac spine (ASIS) bilaterally, center of the patella, and center of thetalocrural joint in the frontal plane, and some markers were placed on the dominant side greatertrochanter, lateral femoral epicondyle, and lateral malleolus in the sagittal plane for 2D kinematicanalysis.

The LESS is used to evaluate the landing technique of an individual based on 17 easily observablecriteria. The participants were asked to jump forward from a 30-centimeter-tall box, land on a markedspot on the ground that was half their height away from the box, and immediately jump vertically as highas possible (Fig. 3). At this stage, the score of the subjects was calculated out of a total of 17, and wasinversely proportional to the LESS performance. The scoring criteria and description of the LESS havebeen previously reported [21]. The LESS provides a valid, two-dimensional assessment of lower extremityand trunk kinematics and has excellent intraclass correlation-coe�cient (ICC) (SEM = 0.42) and goodinterrater reliability ICC (SEM = 0.71) [22]. In the present study, ImageJ software was used to measureknee �exion, trunk �exion, and ankle dorsi�exion in the sagittal plane and trunk inclination and kneevalgus in the frontal plane. None of the participants were instructed on proper landing techniques.

2.5. Electromyography of Muscles (EMG)

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Wireless surface EMG electrodes were oriented parallel to the muscle �bres and placed on the GM, RF,and ST muscles of the dominant leg in accordance with the SENIAM recommendations. The GM waspositioned 50% on the line from the iliac crest to the trochanter, RF was placed at 50% of the distance ona straight line between the ASIS and the proximal patellar margin, and ST placed at 50% of the distanceon a straight between the ischial tuberosity and medial epicondyle [23].

After shaving and cleaning the sites with 70% alcohol to reduce skin impedance, gel-type Ag/AgClelectrodes (diameter: 20 mm; Skintact, Austria) were attached to the muscles belly of the dominant leg.The surface EMGs were ampli�ed 500 times, sampled at 1500 Hz, and digitized using a 16-bit analog to adigital converter. The signals were �ltered at the bandwidth of 10–500 Hz to eliminate the noise recordedduring data collection, and the root mean square window of 50 milliseconds was used for signalsmoothing. The mean value of each period was also calculated during the test [2]. The subjectsperformed the one-leg stance for 30 seconds, and the EMG data were normalized to the peak muscleactivity (maximum voluntary isometric contraction).

2.6. Statistical AnalysisData analysis was performed using SPSS version 21.0 (SPSS Inc., Chicago, USA) employing the Shapiro-Wilk test to assess the normality of data distribution and Levene’s test for the homogeneity of data. Inaddition, descriptive statistics were calculated for all variables, and mean and standard deviation (SD)and 95% con�dence interval (CI) were reported. The homogeneity of the demographic data at baselinewas evaluated using independent samples t-test, which was also employed to compare the means of thelanding mechanics and muscle EMG variables between the participants with and without lumbopelviccontrol. In all the statistical analyses, the signi�cance level was set at 0.05.

The sample size of the study was estimated at 17 participants per group based on the study by Grosdentet al. [11], and the effect size (ES) was calculated using the following formula:

ES with d < 0.2 was considered to be small, while d > 0.5 was moderate, and d > 0.8 was considered large[11].

3. ResultsIn total, 34 female basketballs, volleyball, and handball players completed the study. The results of theShapiro-Wilks and Levene’s tests con�rmed both research hypotheses (P > 0.05). In addition, thecomparison of the participants with and without lumbopelvic control indicated no signi�cant differences

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regarding age, weight, height, body mass index, activity hours in the week, and duration of activity (P > 0.05) (Table 1).

Table 1Descriptive statistics of participants with and without lumbopelvic control.

  Without-LPC (n = 17)

Mean SD

With-LPC (n = 17)

Mean SD

P-Value

Age (years) 18.29 2.41 18.29 4.10 1.00

Weight (kg) 67.76 16.79 65.82 9.25 0.62

Height (cm) 173.23 8.26 173.76 6.24 0.84

BMI(kg.m− 2) 22.33 4.13 21.72 2.47 0.66

Activity (h.wk− 1) 5.27 1.92 5.55 2.14 0.67

Duration of

activity (years)

7.47 2.42 7.17 1.81 0.79

KLAT (mmHg) 10.17 2.65 3.76 2.99 0.0001

BKFO(mmHg) 14.47 2.85 2.94 2.13 0.0001

ASLR(mmHg) 10.88 2.28 3.76 2.99 0.0001

PRONE(mmHg) 17.76 3.88 6.35 3.25 0.0001

Note: LPC, lumbopelvic control; SD, standard deviation; BMI, body mass index; h, hours; wk, week.KLAT, Knee Lift Abdominal Test; BKFO, Bent Knee Fall Out; ASLR, Active Straight Leg Raising.

3.1. Muscle ActivityA signi�cant difference was observed between the subjects with and without lumbopelvic control only interms of the GM activity (t32 = 2.26; 95% CI: 0.26–4.89; P = 0.032; ES = 0.13). However, no signi�cantdifferences were observed between the groups in terms of the RF and ST muscle activity (P > 0.05)(Table 2 & Fig. 4).

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Table 2Comparison in muscles activity during single-leg standing and landing mechanic between with and

without lumbopelvic control groups.

  Without-LPC (n = 17)

Mean SD

With-LPC (n = 17)

Mean SD

P-Value ES

Electromyography*            

GM 5.89 2.22 8.47 4.12 0.032* 0.13

RF 3.23 1.52 5.21 6.06 0.20 0.05

ST 7.61 5.36 7.42 6.14 0.92 0.00

Landing mechanic            

Trunk lateral �exion 29.40 3.78 22.60 2.77 0.0001** 0.37

Knee valgus 23.26 8.02 9.40 5.70 0.0001** 0.48

Trunk �exion 74.66 11.17 87.40 15.49 0.015* 0.16

Knee �exion 71.40 15.52 92.40 16.70 0.001** 0.28

Ankle dorsi�exion 79.86 10.58 78.26 9.88 0.67 0.00

LESS 8.20 2.11 2.00 1.25 0.0001** 0.74

Note: LPC, lumbopelvic control; SD, standard deviation; ES, effect size; GM, gluteus medius; RF, rectusfemoris; ST, semitendinosus; MVIC, maximum voluntary isometric contraction; LESS, landing errorscoring system. * Percent activation relative to MVIC. *P < 0.05 & **P < 0.001.

3.2. Landing KinematicsThe analysis of the knee valgus indicated a signi�cant difference between the subjects with and withoutlumbopelvic control (t32=-5.45; 95% CI: -19.07–8.66; P = 0.0001; ES = 0.48). Furthermore, a signi�cantdifference was observed between the subjects with and without lumbopelvic control regarding the lateral�exion angle of the trunk in the frontal plane (t32 = 7.09; 95% CI: 5.54–10.05; P = 0.0001; ES = 0.61).Signi�cant differences were also denoted between the two groups in terms of the trunk �exion angle (t32 = 2.58; 95% CI: 2.63–22.83; P = 0.015; ES = 0.16) and knee �exion angle in the sagittal plane (t32 = 3.56;95% CI: 8.93–33.06; P = 0.001; ES = 0.28), while no signi�cant difference was observed in ankledorsi�exion (P > 0.05). In the LESS test, a signi�cant difference was also observed between the subjectswith and without lumbopelvic control (t32=-9.78; 95% CI: -7.49–4.90; P = 0.0001; ES = 0.74) (Table 2 &Fig. 4).

4. Discussion

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The present study aimed to evaluate the status of lumbopelvic control in professional athletes withfrequent jump-landing skills and compare the mechanical status of the landing and lower limb muscleactivity of the athletes with and without lumbopelvic control to recognize the associated risk factors.Lumbopelvic control was assessed by four tests using a PBU in which pressure changes of more than 8mmHg indicated poor lumbopelvic control. Based on these results, the athletes participating in the studywere divided into two groups of poor lumbopelvic control and adequate lumbopelvic control.

The current study indicated that professional female basketball, volleyball, and handball players havepoor lumbopelvic control. The lumbopelvic region provides dynamic stability for the movement of theextremities [18]. Recent �ndings have demonstrated that the risk of injury increases with the disruption ofthe elements within the kinetic chain, which in turn causes alterations in the biomechanics of theextremities. Poor control of the lumbopelvic area is associated with upper limb injuries [8, 20, 24].Furthermore, trunk muscle activity precedes lower limb muscle activity, and the central nervous systemprovides a stable foundation for lower limb movements [13]. Therefore, the disrupted stability of thisfoundation could lead to ine�cient landing and predispose the individual to lower limb injury. In jumplanding, 50% of knee injuries occur following landing on the opposite, and the other 50% arise fromimproper landing [4].

According to �nding in the current research, landing mechanics (i.e., LESS test scores) in the subjectswithout lumbopelvic control were signi�cantly weaker compared to those with lumbopelvic control, whichcon�rms the research hypothesis. This may result from poor control of the lumbopelvic region asweaknesses or delays in the activation of the muscles involved in lumbopelvic control could causecompensatory and unpredictable movements. For instance, GM is one of the main lumbopelvic muscles,as well as the main abductor of the hip joint. Dysfunction of this muscle could cause the femur to moveto the midline of the body and increase the dynamic knee valgus moment [25]. A LESS test score greaterthan 5 increases the relative risk of ACL injury 10.7 times. On the other hand, core exercises could reducethe LESS score by up to three points [26]. In other words, the increased stability of the trunk coulddecrease the mechanical errors of landing, which is consistent with our �ndings. Also, impairedneuromuscular control of core stability during dynamic movements may expose athletes to lower limbinjuries [13].

According to the results of the present study, the lateral �exion of the trunk and knee valgus weresigni�cantly higher in the subjects without lumbopelvic control compared to those who had adequatecontrol. Landing on the knee at the frontal plane imposes high strains on the medial collateral ligamentand ACL. Furthermore, maintaining and controlling the trunk plays a key role in reducing the pressure onthe knees, and the risk of lower limb injuries. In particular, the combination of knee valgus and lateraltrunk �exion on the frontal plane is highly sensitive in the identi�cation of women at risk of ACL injuries[27]. In this regard, individuals with lateral trunk �exion have increased knee valgus, and lateral �exion ofthe trunk could cause the ground reaction force to pass through the lateral compartment of the knee andincrease the abduction torque exerted on it [28]. Similarly, poor neuromuscular control of the trunk can be

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associated with knee injuries in women [13]. Dynamic knee valgus of more than eight degrees whilelanding is reliable predictor ACL injury [29].

According to the results of the study, the �exion of the knee and trunk at the sagittal plane was higher inthe subjects with lumbopelvic control compared to those without lumbopelvic control, which con�rmedthe research hypothesis. Knee �exion angle has been associated with knee injuries, with several studiesreporting that and increased knee �exion angle could decrease the anterior shear force on the knee jointand strain the ACL [30–32]. In this regard, with the knee �exed, lower anterior shear forces are applied tothe knee joint compared to the extension position: trunk �exion with knee �exion at the moment oflanding could cause decrease the ACL strain [33]. These �ndings are in line with the results of the presentstudy.

The three important muscles investigated in the current research were RF, ST, and GM, which originatefrom the pelvis and are involved in the occurrence of knee injuries [17, 18, 28, 34]. According to our�ndings, only the GM muscle activity was signi�cantly different between the subjects with and withoutlumbopelvic control regarding the ability to stand on one leg. Many lower limb injuries occur in a single-legged position, especially in sports such as handball, basketball, and volleyball, which involve frequentjumps and landings [35, 36]. The GM muscle plays a vital role in lumbopelvic control, and, given itsabduction torque, it in�uences the mechanics of the lower limb, especially knee valgus. This �nding is inline with the study by Laudner et al., which demonstrated that the GM muscle is a primary pelvic stabilizerduring single-legged standing and also plays a key role in lumbopelvic control [24]. In this regard, optimalstrengthening of the gluteal muscles to enhance the stability of the lumbopelvic region [37]. Thedecreased activity of the GM muscle and instability of the lumbopelvic-hip complex was associated withlower limb injuries [38].

One of the limitations of our study was that, given our country sharia laws, it was not possible to evaluatemen and women, and the women evaluator was only allowed to study women. In addition, we could notstudy more muscles due to economic issues and lack of time during the COVID-19 pandemic. Therefore,it is recommended that further investigations be focused on more muscles to achieve more accurateresults and make comparisons with our �ndings.

5. ConclusionPoor lumbopelvic control in the professional athletes with frequent jump-landings affected the scores ofthe mechanical landing test (LESS), lateral �exion angle of the trunk, angle of dynamic knee valgus, knee�exion angle, �exion angle of the trunk, and EMG of the GM muscle. Therefore, the increased risk of lowerlimb injuries could be predicted by impaired lumbopelvic control. It is recommended that sportsrehabilitation specialists, physiotherapists, and coaches use appropriate strategies to strengthen thelumbopelvic control of athletes to prevent possible injuries.

Abbreviations

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ACL: anterior cruciate ligament; KLAT: knee lift abdominal test; BKFO: bent knee fall-out; ASLR: activestraight leg raising; PBU: pressure biofeedback unit; LESS: landing error scoring system; EMG:electromyography; GM: gluteus medius; RF: rectus femoris; ST: semitendinosus; PSIS: posterior superioriliac spines; ASIS: anterior superior iliac spine; ICC: intraclass correlation-coe�cient; SD: standarddeviation; CI: con�dence interval; ES: effect size.

Declarations

Ethics approval and consent to participateThe objectives and procedures of this study were explained to the participants, and written informedconsent was obtained from all participants before the beginning of the study that was in accordance withthe Declaration of Helsinki. The research protocol was approved by the Ethics Committee of RaziUniversity of Iran (code: IR.RAZI.REC.1399.007).

Consent for publicationThe person on the pictures has provided written consent for publication.

Availability of data and materialsThe datasets used and/or analysed during the current study are available from the corresponding authoron reasonable request.

Competing interestsThe authors declare that they have no competing interests.

FundingThe present study was �nancially supported by Razi University.

Authors’ contributionsPF recruited the patients, collected the data and designed the idea, FG was supervisor, designed the idea,and assessed the outcomes of the research. NM assessed the outcomes of the research and reviewed thepaper. All the authors contributed to the writing of the paper.

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AcknowledgmentsHereby, we extend our gratitude to the athletes for participating in this study, their coaches whocoordinated their participation, and the expert of the Sports Rehabilitation Laboratory for assisting us inthis research process.

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Figures

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Figure 1

Study �ow chart.

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Figure 2

A) Knee Lift Abdominal Test, B) Bent Knee Fall-out Test, C) Active Straight Leg Raising test, D) PRONETest.

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Figure 3

Landing Error Scoring System Demonstration.

Figure 4

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Comparison of Study Variables (mean): (A), muscles activity (% MVIC); (B), Landing mechanics/ Sagittalview; (C), Landing mechanics/ Frontal view; (D), Landing error scoring system (LESS) scores betweensubjects with and without lumbopelvic control (*P<0.05 and **P<0.001, respectively; error bars indicatestandard deviations).