Journal of Applied Biomechanics, 2015, 31, 244 -249 http://dx.doi.org/10.1123/jab.2014-0272 © 2015 Human Kinetics, Inc.
ORIGINAL RESEARCH
Sex Differences During an Overhead Squat Assessment Timothy C. Mauntel,1 Eric G. Post,2 Darin A. Padua,1 and David R. Bell2 1University
of North Carolina; 2University of Wisconsin–Madison
A disparity exists between the rates of male and female lower extremity injuries. One factor that may contribute to this disparity is high-risk biomechanical patterns that are commonly displayed by females. It is unknown what biomechanical differences exist between males and females during an overhead squat. This study compared lower extremity biomechanics during an overhead squat and ranges of motion between males and females. An electromagnetic motion tracking system interfaced with a force platform was used to quantify peak lower extremity kinematics and kinetics during the descent phase of each squat. Range of motion measurements were assessed with a standard goniometer. Differences between male and female kinematics, kinetics, and ranges of motion were identified with t tests. Males displayed greater peak knee valgus angle, peak hip flexion angle, peak vertical ground reaction forces, and peak hip extension moments. Males also displayed less active ankle dorsiflexion with the knee extended and hip internal and external rotation than females. No other differences were observed. The biomechanical differences between males and females during the overhead squat may result from differences in lower extremity ranges of motion. Therefore, sex-specific injury prevention programs should be developed to improve biomechanics and ranges of motion. Keywords: biomechanics, kinematics, kinetics Lower extremity musculoskeletal injuries are the most significant medical issues affecting intercollegiate athletes1,2 and military personnel.3 Musculoskeletal injuries result in substantial medical costs, physical and mental anguish, and forced attrition from physical activity.1,4,5 Traumatic noncontact and overuse lower extremity injuries also carry long-term physical6,7 and financial consequences.8 The short- and long-term consequences of musculoskeletal injuries make it essential to identify risk factors associated with them. Two commonly proposed risk factors for lower extremity injuries include high-risk biomechanical patterns9–12 and sex.4,10,13–15 Collectively, these risk factors likely contribute significantly to the disparity seen in the rate of noncontact lower extremity injuries between males and females. Specifically, females have higher rates of lower extremity musculoskeletal injuries compared with their male counterparts.4,10,13–15 This issue is becoming increasingly apparent and problematic as the number of females participating in athletics4,16 and physically-demanding roles in the military17 continues to rise. It is likely that differences in lower extremity biomechanics between males and females influence the rates of noncontact injuries.13,18–20 It is therefore essential that biomechanical differences between the sexes are better understood so that sex-specific injury prevention programs can be developed and implemented.
Timothy C. Mauntel and Darin A. Padua are with the Department of Exercise and Sport Science, Sports Medicine Research Laboratory, University of North Carolina, Chapel Hill, NC. Eric G. Post is with the Department of Kinesiology, Wisconsin Injury in Sport Laboratory, University of Wisconsin–Madison, Madison, WI. David R. Bell is with the Department of Kinesiology and Department of Orthopedics and Rehabilitation, Wisconsin Injury in Sport Laboratory, University of Wisconsin–Madison, Madison, WI. Address author correspondence to Timothy C. Mauntel at tmauntel@ gmail.com. 244
High-risk biomechanical patterns result in irregular musculoskeletal stresses21 and increase the risk of sustaining noncontact and overuse lower extremity injuries.10,11,22 Females more commonly display these high-risk biomechanical patterns than do males.19,20,23–27 Commonly observed high-risk biomechanical patterns displayed by females, compared with males, during movement assessments include greater knee valgus angle,19,23 greater hip adduction angle,19 greater hip internal rotation motion,19,20 and less hip flexion motion.20,23 The differences in biomechanical patterns observed between males and females have been observed during single-leg squat assessments,19,27 jumping assessments,23–25 and cutting tasks.20,26 However, it is relatively unknown what differences, if any, exist between males and females during overhead squat assessments. Determining differences in male and female biomechanics during overhead squat assessments is important, as these assessments are commonly used in clinical28,29 and research settings.30–32 Furthermore, the overhead squat is similar to the single-leg squat in that it is slower than jumping and cutting assessments so it may be easier for clinicians to identify some of the aforementioned highrisk biomechanical patterns that can place individuals at increased risk of lower extremity injury.33 Range of motion measurements are important to consider when completing lower extremity biomechanical assessments, as they are related to high-risk biomechanical patterns.31,32,34 Range of motion measurements can aid clinicians in explaining biomechanical patterns observed during movement assessments. Understanding biomechanical and range of motion differences between males and females is important, because once these factors are understood clinicians can better plan and implement sex-specific injury prevention strategies. Specialized injury prevention programs can effectively reduce the rate of noncontact lower extremity injuries.35,36 Reducing the rate of musculoskeletal injuries will decrease the short- and long-term consequences of injury while increasing physical fitness and performance. Therefore, the purpose of this study was to determine if biomechanical differences exist between a population of physically
Sex Differences During an Overhead Squat 245
active males and females during an overhead squat assessment. This population is representative of physically active individuals in general as well as those that may be entering military basic training. We hypothesized females would display biomechanical patterns that are known to increase the risk of noncontact lower extremity injuries, while males would not. Generally, we hypothesized that females would have greater frontal plane hip and knee motion and less sagittal plane hip and trunk motion compared with males. Secondarily, range of motion measurements were assessed to provide further explanations of biomechanical differences observed between males and females. We hypothesized that females would have greater ankle dorsiflexion, hip internal rotation, and hip abduction, and less hip external rotation compared with males.
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Methods The study sample was a subset of individuals from a larger previously-reported sample.37 Stiffler et al37 recruited 100 recreationally active individuals (males = 30, females = 70) from the general university population. All participants scored ≥ 4 on the Tegner Activity Level survey38 and self-reported to be in good physical condition. Individuals were excluded if they reported current symptoms of injury to the lower extremity or low back, had an injury to the lower extremity or low back within the past 6 months that resulted in 3 or more consecutive days of missed activity, or had a previous surgical operation to the lower extremity or low back. Persons with known neurologic conditions were also excluded. This study was approved by the university’s institutional review board and each participant signed an informed consent form approved by the institutional review board.
Sample Subset Identification Following the initial data collection and reduction,37 a subset of 60 individuals (males = 30, females = 30) was identified; female participants were matched to male participants based on Tegner score (primary) and body mass index (BMI; secondary). Four male participants had missing data; these 4 males and their matched females were excluded from analyses. Six additional participants (males = 3, females = 3) were identified as being outliers (≥ 3 standard deviations away from the mean) for one or more outcome measures and, along with their matches, were also excluded from analyses. For one matched pair, the male participant was identified as an outlier for one variable and the female participant was identified as an outlier for a separate variable. A final sample size of 42 (males = 21, females = 21) was used for statistical analyses (Table 1).
Data Collection Procedures Following informed consent, demographic information (height [cm], mass [kg], age [y], leg dominance [the leg used to kick a soccer ball for maximal distance], and physical activity level) was collected for each participant. Participants wore their own t-shirt, shorts, and athletic shoes during data collection. Biomechanical and range of motion measures were completed on each participant’s dominant limb. The biomechanical and range of motion data collection procedures are identical to those previously reported.37
Biomechanical Data Collection Biomechanical data collection consisted of 5 overhead squats completed in succession. For the overhead squats, all participants started in a standardized position with their feet shoulder-width apart, toes pointed forward, heels on the floor, and arms extended overhead. Participants were instructed to squat in a deep, slow, and controlled manner, to a depth that was comfortable. A trial was deemed successful if the participant: (1) maintained the head facing forward; (2) kept the arms extended overhead; (3) kept the heels on the floor; (4) completed the assessment at the appropriate speed; and (5) completed the assessment in a fluid motion.30 An electromagnetic tracking system (Ascension Technologies, Inc., Burlington, VT) controlled by MotionMonitor software (Innovative Sports Training, Inc., Chicago, IL) was used in conjunction with a nonconductive force platform (Bertec Corporation, Columbus, OH) to quantify lower extremity three-dimensional kinematics and kinetics of the dominant limb during the overhead squat. Electromagnetic sensors were placed over the C7 spinous process, sacrum, lateral aspect of the thigh, and the anteromedial aspect of the proximal tibia and secured with double-sided tape, prewrap, and athletic tape. A segment-linkage model of the pelvis and dominant lower extremity was generated by digitizing the T12/L1 joint, the anterior superior iliac spines, femoral epicondyles, and malleoli. The location of the hip joint center was approximated using the Bell method.39 The knee joint center was defined as the midpoint of the femoral epicondyles and the ankle joint center was defined as the midpoint of the malleoli. Kinematic and kinetic data were sampled at 144 Hz and 1440 Hz, respectively. A right-handed global reference system was defined with the positive x-axis in the anterior direction, the positive y-axis to the left of each participant, and the positive z-axis in the superior direction. Euler angles were used with orders of rotation: Y (flexion/extension), X (abduction/adduction), and Z (internal/external rotation). Motion about the hip was defined as the thigh relative to the pelvis, and motion about the knee as the shank relative to the
Table 1 Subject demographics presented as means ± standard deviation and 95% confidence intervals Males
Females
Mean (95% CI)
Mean (95% CI)
P-value
182.56 ± 6.67 (179.71, 185.41)
166.92 ± 3.99 (165.22, 168.63)
< .001
Mass*
80.47 ± 6.93 (77.50, 83.43)
67.14 ± 7.18 (64.07, 70.21)
< .001
Age
20.29 ± 1.59 (19.61, 20.97)
20.19 ± 0.98 (19.77, 20.61)
.816
6.05 ± 1.20 (5.54, 6.56)
6.05 ± 1.20 (5.54, 6.56)
1.000
24.16 ± 1.98 (23.21, 25.01)
24.05 ± 1.95 (23.22, 24.88)
.858
Height*
Tegner score Body mass index
*Indicates significance at α ≤ .05. JAB Vol. 31, No. 4, 2015
246 Mauntel et al
thigh. Trunk motion was calculated relative to the global reference frame. Full extension of the hip, knee, and trunk were defined as 0° when the individual was standing in an erect, neutral position. Custom Matlab (Version 2013a, The MathWorks, Natick, MA) software was used to filter (fourth-order low-pass Butterworth filter with a cutoff frequency of 14.5 Hz) and identify the peak values of the dependent variables of interest during the “descent phase” of each squat. The descent phase was defined as the time from the start of knee flexion motion to the point of greatest knee flexion. Inverse dynamics was used to calculate net internal joint moments (N∙m) during the squat; internal joint moments were normalized to a product of body height (m) and body mass (kg). Ground reaction forces were normalized to body mass (kg). Peak kinematic and kinetic variables were averaged across the 5 overhead squat trials for each participant.
the axis was placed over the dominant limb anterior superior iliac spine, and the movement arm was placed along the midline of the anterior thigh. The dominant limb was passively abducted until the contralateral anterior superior iliac spine moved inferiorly.
Statistical Analyses Independent samples t tests (PASW Statistics for Windows version 21.0, IBM, Inc., Chicago, IL) were used to compare males and females. Averaged peak sagittal, frontal, and transverse plane knee, hip, and trunk joint angles, as well as averaged normalized peak vertical ground reaction forces and net internal joint moments, were compared between groups. Average joint range of motion values were also compared. Statistical significance was set a priori at α ≤ .05.
Results
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Range of Motion Data Collection Lower extremity range of motion was assessed with a standard 12-in goniometer. Three measurements were taken for each motion assessed. The 3 independent trials were averaged and the average value was used for statistical analyses. Study participants were supine for all range of motion assessments. The following procedures were used to assess ankle dorsiflexion, hip internal and external rotation, and hip abduction:32 Ankle Active and Passive Dorsiflexion. Ankle dorsiflexion was
measured with the knee extended and flexed to approximately 30°. The stationary arm of the goniometer was placed along the length of the lateral fibula, the axis was positioned over the lateral malleolus, and the movement arm was placed parallel to the lateral aspect of the fifth metatarsal. The dominant limb foot was actively and passively dorsiflexed until the end range was determined.
Hip Internal and External Rotation. The dominant limb was flexed to 90° at the hip and knee and the hip was in neutral alignment relative to the pelvis. The stationary arm of the goniometer was placed parallel to the table, the axis was placed over the center of the patella, and the movement arm was placed along the midline of the anterior shank. The dominant limb hip was passively internally and externally rotated until the end range was determined. Hip Abduction. The dominant limb was fully extended on the table. The stationary arm of the goniometer was placed along a line connecting the right and left anterior superior iliac spines,
For descriptive statistics, males were taller and heavier than the matched females (Table 1). No differences were observed for activity level or BMI since these variables were used as matching criteria. Significant differences were observed between groups for peak knee valgus angle, peak hip flexion angle, normalized peak vertical ground reaction forces, and normalized peak hip extension moment. There were no significant differences between groups for peak knee flexion or internal rotation angles, peak hip adduction or internal rotation angles, or peak trunk forward or lateral flexion angles. Significant differences were also not observed for normalized peak knee extension, knee valgus, knee internal rotation, or hip adduction moments (Tables 2 and 3). Significant differences also existed between males and females for active ankle dorsiflexion with the knee extended and hip internal and external rotation. There were no significant differences for active ankle dorsiflexion with the knee flexed, passive ankle dorsiflexion with the knee extended or flexed, or hip abduction (Table 4).
Discussion The overhead squat is a common functional movement assessment used to identify individuals displaying high-risk biomechanical patterns that may place them at greater risk of injury.28–32 The results of our study show that the overhead squat can be used to discriminate biomechanical differences between males and females. These bio-
Table 2 Peak joint angles presented as means ± standard deviation and 95% confidence intervals Males
Females
Mean (95% CI)
Mean (95% CI)
P-value
Knee flexion
110.26 ± 19.24 (102.03, 118.49)
100.64 ± 14.79 (94.31, 106.97)
.077
Knee valgus*
–12.62 ± 11.00 (–17.32, –7.92)
–4.86 ± 4.12 (–6.62, –3.12)
.004
4.20 ± 6.24 (1.53, 6.87)
4.64 ± 7.51 (1.43, 7.85)
.839
–117.02 ± 9.88 (–121.25, –112.79)
–105.19 ± 13.69 (–111.05, –99.33)
.003
Knee internal rotation Hip flexion* Hip adduction
6.89 ± 8.16 (3.40, 10.38)
5.31 ± 5.30 (3.04, 7.58)
.463
Hip internal rotation
13.42 ± 6.67 (10.57, 16.27)
10.71 ± 7.08 (7.68, 13.74)
.208
Trunk flexion
21.33 ± 13.30 (15.64, 27.02)
24.73 ± 16.49 (17.68, 31.78)
.467
4.14 ± 4.82 (2.08, 6.20)
3.79 ± 5.13 (1.60, 5.98)
.818
Trunk lateral flexion *Indicates significance at α ≤ .05.
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Sex Differences During an Overhead Squat 247
Table 3 Peak normalized ground reaction forces and internal joint moments presented as means ± standard deviation and 95% confidence intervals Males
Females
Mean (95% CI)
Mean (95% CI)
P-value
0.67 ± 0.07 (0.63, 0.70)
0.62 ± 0.06 (0.60, 0.64)
.027
Knee extension moment
–0.12 ± 0.03 (–0.13, –0.11)
–0.11 ± 0.02 (–0.12, –0.10)
.273
Knee valgus moment
–0.02 ± 0.01 (–0.02, –0.01)
–0.02 ± 0.01 (–0.02, –0.01)
.599
Knee internal rotation moment
0.02 ± 0.01 (0.01, 0.02)
0.01 ± 0.01 (0.01, 0.02)
.484
Hip extension moment*
0.12 ± 0.04 (0.11, 0.14)
0.09 ± 0.02 (0.08, 0.10)
< .001
Hip adduction moment
0.03 ± 0.02 (0.02, 0.03)
0.02 ± 0.01 (0.01, 0.03)
.224
Vertical ground reaction force*
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*Indicates significance at α ≤ .05. Note. Ground reaction forces were normalized to body mass (kg) and internal joint moments were normalized to a product of body height (m) and body mass (kg).
Table 4 Range of motion measurements presented as means ± standard deviation and 95% confidence intervals Males
Females
Mean (95% CI)
Mean (95% CI)
Active ankle dorsiflexion—knee extended*
0.24 ± 5.96 (–1.57, 2.04)
3.79 ± 5.27 (2.20, 5.39)
.047
Active ankle dorsiflexion—knee flexed
6.48 ± 6.66 (4.46, 8.49)
8.13 ± 6.67 (6.11, 10.15)
.427
Passive ankle dorsiflexion—knee extended
7.29 ± 5.97 (5.48, 9.09)
9.82 ± 6.07 (7.99, 11.66)
.179
Passive ankle dorsiflexion knee flexed
12.11 ± 7.45 (9.86, 14.36)
13.35 ± 8.10 (10.90, 15.80)
.609
Hip external rotation*
36.92 ± 11.61 (33.41, 40.43)
46.19 ± 14.70 (41.75, 50.64)
.029
Hip internal rotation*
28.78 ± 11.45 (25.05, 31.97)
37.51 ± 10.76 (34.25, 40.76)
.015
Hip abduction
32.84 ± 6.62 (30.84, 34.84)
36.93 ± 8.65 (35.32, 39.55)
.093
P-value
*Indicates significance at α ≤ .05.
mechanical differences are likely influenced in part by the differences observed in lower extremity ranges of motion. Biomechanical and range of motion differences between males and females may also help to explain the discrepancies observed between male and female noncontact lower extremity injury rates.4,13–15 Males displayed greater peak knee valgus angles (males = –12.62 ± 11.00°, females = –4.86 ± 4.12°) and greater peak hip flexion angles (males = –117.02 ± 9.88°, females = –105.19 ± 13.69°) than the females. These findings only partially support our hypothesis. The greater average peak knee valgus angle displayed by males does not support our hypothesis, as a greater peak valgus angle has been identified as a risk factor for noncontact lower extremity injuries.10,11,40–42 However, the greater hip flexion angles displayed by males does support our hypothesis since greater sagittal plane hip and knee motion is suggested as a protective mechanism for noncontact lower extremity injuries.24,43,44
Medial knee displacement is a visually observed movement pattern that is commonly used as a proxy for knee valgus motion.30,33,34 Previous research has shown that individuals who display medial knee displacement during a single-leg squat also display greater knee valgus motion, compared with individuals who maintain a neutral knee alignment.33 Furthermore, previous research has established a link between medial knee displacement during movement assessments and limited ankle dorsiflexion.31,32,34,37 Our current study found similar results. Male participants displayed greater knee valgus angles and less active ankle dorsiflexion with the knee extended (0.24 ± 5.96°) compared with females (3.79 ± 5.27°). Restricted ankle dorsiflexion could inhibit the tibia from moving forward over the foot and result in compensatory motions, including increased foot pronation, talar eversion, and tibial internal rotation.45 Ultimately, these compensatory foot and ankle motions could result in greater frontal and transverse plane motions at the hip and knee.34 These compensatory foot and ankle motions, in combination with the greater hip and knee sagittal plane motion, may have contributed to the greater valgus angles displayed by the males. Overall, males displayed less hip mobility than females. Specifically, males displayed less hip internal and external rotation. Limited transverse plane hip mobility, especially limited internal rotation motion, has been shown to increase an individual’s risk of noncontact anterior cruciate ligament injury.46–48 Gomes et al48 also showed that individuals with a restricted total arc of hip rotation were at increased risk of sustaining a noncontact knee injury. It has been suggested that similar to how restricted ankle mobility can alter proximal joint angles (ie, the knee),34 restricted hip mobility can alter distal joint angles (ie, the knee) during functional tasks.46 Furthermore, while not significantly different between the sexes, males displayed ~4° less hip abduction motion than females (P = .093). This finding is similar to one previously reported by Mauntel et al,34 who compared range of motion differences between individuals who displayed medial knee displacement during a singleleg squat and those who did not. The combination of restricted hip ranges of motion and limited active ankle dorsiflexion displayed by the males likely contributed to the greater frontal plane knee motion (ie, valgus) we observed. Males have been shown to display greater sagittal plane hip motion during movement assessments compared with females.19,20,26 However, males have not displayed greater sagittal plane hip motion compared with females during all movement assessments.23,26,27 Kernozek et al23 found that females displayed a 14° more peak hip
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248 Mauntel et al
flexion angle compared with males during a drop-landing task. One potential explanation for the difference observed in peak hip flexion angle between the previous research23 and our study is static stance posture. In our study the male participants displayed greater minimum hip flexion angles (–8.31 ± 6.34°) compared with females (–3.89 ± 6.40°), which disagrees with previous research23 that observed females had greater hip flexion angles in a static position. Our study and the work of others23,26 suggest that resting joint positions are important to consider when evaluating movement assessments. Males also had greater normalized peak vertical ground reaction forces (males = 0.67 ± 0.07, females = 0.62 ± 0.06) and normalized peak hip extension moments (males = 0.12 ± 0.04, females = 0.09 ± 0.02) than the females. Our finding of males displaying greater normalized peak internal hip extension moments is similar to what has been previously reported during cutting20 and jumping49 tasks. Males may display greater hip extension moments because of greater passive restraints resulting from greater sagittal plane stiffness49 and restrictions in hip ranges of motion, as observed in our study, compared with females. However, the exact mechanism for why males display greater peak internal hip extension moments during a variety of dynamic tasks remains unknown. The major limitation of this study is that only one movement assessment was examined. Additional differences in biomechanics may have been identified between sexes had additional movement assessments been used. In addition, biomechanical data were not collected from the foot and additional differences in lower extremity biomechanics may have been observed had these data been collected. Furthermore, the capability of the biomechanical and range of motion differences observed between sexes to predict future injury was also not assessed in this study. Determining the ability of these differences to discriminate between individuals who go on to sustain an injury and those who do not should be determined. The overhead squat assessment is commonly used by sports medicine professionals to identify individuals who display biomechanical patterns that may place them at greater risk of lower extremity injury.28–32 The overhead squat has the ability to identify biomechanical differences between males and females; however, it has yet to be determined if these biomechanical differences are clinically meaningful. Until the overhead squat is more formally developed into a movement assessment capable of identifying lower extremity injury risk factors, clinicians should continue to use multiple movement assessments to develop an accurate profile of an individual’s movement patterns. Acknowledgments This research was supported by the Virginia Horne Henry Fund for Women’s Physical Education.
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Sex Differences During an Overhead Squat 249 21. Guilak F, Fermor B, Keefe FJ, et al. The role of biomechanics and inflammation in cartilage injury and repair. Clin Orthop Relat Res. 2004; (423):17–26. PubMed doi:10.1097/01.blo.0000131233.83640.91 22. Friedl KE, Evans RK, Moran DS. Stress fracture and military medical readiness: bridging basic and applied research. Med Sci Sports Exerc. 2008;40(11 Suppl):S609–S622. PubMed doi:10.1249/ MSS.0b013e3181892d53 23. Kernozek TW, Torry MR, Iwasaki M. Gender differences in lower extremity landing mechanics caused by neuromuscular fatigue. Am J Sports Med. 2008;36(3):554–565. PubMed doi:10.1177/0363546507308934 24. Padua DA, Marshall SW, Boling MC, Thigpen CA, Garrett WE, Jr, Beutler AI. The Landing Error Scoring System (LESS) is a valid and reliable clinical assessment tool of jump-landing biomechanics: The JUMP-ACL study. Am J Sports Med. 2009;37(10):1996–2002. PubMed doi:10.1177/0363546509343200 25. Theiss JL, Gerber JP, Cameron KL, et al. Jump-landing differences between varsity, club, and intramural athletes: the Jump-ACL Study. J Strength Cond Res. 2014;28(4):1164–1171. PubMed 26. Iguchi J, Tateuchi H, Taniguchi M, Ichihashi N. The effect of sex and fatigue on lower limb kinematics, kinetics, and muscle activity during unanticipated side-step cutting. Knee Surg Sports Traumatol Arthrosc. 2014;22(1):41–48. PubMed doi:10.1007/s00167-013-2526-8 27. Graci V, Van Dillen LR, Salsich GB. Gender differences in trunk, pelvis and lower limb kinematics during a single leg squat. Gait Posture. 2012;36(3):461–466. PubMed doi:10.1016/j.gaitpost.2012.04.006 28. National Academy of Sports Medicine. NASM Essentials of Corrective Exercise Training, First Edition. Philadelphia, PA: Lippincott Williams & Wilkins; 2010. 29. Hirth CJ. Clinical movement analysis to identify muscle imbalances and guide. Athl Ther Today. 2007;12(4):10–14. 30. Padua DA, Bell DR, Clark MA. Neuromuscular characteristics of individuals displaying excessive medial knee displacement. J Athl Train. 2012;47(5):525–536. PubMed 31. Bell DR, Padua DA, Clark MA. Muscle strength and flexibility characteristics of people displaying excessive medial knee displacement. Arch Phys Med Rehabil. 2008;89(7):1323–1328. PubMed doi:10.1016/j.apmr.2007.11.048 32. Bell DR, Vesci BJ, Distefano LJ, Guskiewicz KM, Hirth CJ, Padua DA. Muscle activity and flexibility in individuals with medial knee displacement during the overhead squat. Athl Train and Sports Health Care. 2012;4(3):117–125. doi:10.3928/19425864-20110817-03 33. Mauntel TC, Frank BS, Begalle RL, Blackburn JT, Padua DA. Kinematic differences between those with and without medial knee displacement during a single leg squat. J Appl Biomech. 2014;30(6):707– 712. PubMed doi:10.1123/jab.2014-0003 34. Mauntel TC, Begalle RL, Cram TR, et al. The effects of lower extremity muscle activation and passive range of motion on single leg squat performance. J Strength Cond Res. 2013;27(7):1813–1823. PubMed 35. DiStefano LJ, Padua DA, DiStefano MJ, Marshall SW. Influence of age, sex, technique, and exercise program on movement patterns
after an anterior cruciate ligament injury prevention program in youth soccer players. Am J Sports Med. 2009;37(3):495–505. PubMed doi:10.1177/0363546508327542 36. Myer GD, Ford KR, Brent JL, Hewett TE. Differential neuromuscular training effects on ACL injury risk factors in “high-risk” versus “low-risk” athletes. BMC Musculoskelet Disord. 2007;8:39. PubMed doi:10.1186/1471-2474-8-39 37. Stiffler MR, Pennuto AP, Smith MD, Olson ME, Bell DR. Range of motion, postural alignment, and LESS score differences of those with and without excessive medial knee displacement. Clin J Sport Med. 2015;25(1):61–66. PubMed 38. Tegner Y, Lysholm J. Rating systems in the evaluation of knee ligament injuries. Clin Orthop Relat Res. 1985; (198):43–49. PubMed 39. Bell AL, Pedersen DR, Brand RA. A comparison of the accuracy of several hip center location prediction methods. J Biomech. 1990;23(6):617–621. PubMed doi:10.1016/0021-9290(90)90054-7 40. Ireland ML. Anterior cruciate ligament injury in female athletes: epidemiology. J Athl Train. 1999;34(2):150–154. PubMed 41. Noehren B, Barrance PJ, Pohl MP, Davis IS. A comparison of tibiofemoral and patellofemoral alignment during a neutral and valgus single leg squat: an MRI study. Knee. 2012;19(4):380–386. PubMed doi:10.1016/j.knee.2011.05.012 42. Laprade RF, Wijdicks CA. The management of injuries to the medial side of the knee. J Orthop Sports Phys Ther. 2012;42(3):221–233. PubMed doi:10.2519/jospt.2012.3624 43. Chappell JD, Creighton RA, Giuliani C, Yu B, Garrett WE. Kinematics and electromyography of landing preparation in vertical stop-jump: risks for noncontact anterior cruciate ligament injury. Am J Sports Med. 2007;35(2):235–241. PubMed doi:10.1177/0363546506294077 44. McLean SG, Walker KB, van den Bogert AJ. Effect of gender on lower extremity kinematics during rapid direction changes: an integrated analysis of three sports movements. J Sci Med Sport. 2005;8(4):411– 422. PubMed 45. DiGiovanni CW, Langer P. The role of isolated gastrocnemius and combined Achilles contractures in the flatfoot. Foot Ankle Clin. 2007;12(2):363–379 viii. PubMed doi:10.1016/j.fcl.2007.03.005 46. Bedi A, Warren RF, Wojtys EM, et al. Restriction in hip internal rotation is associated with an increased risk of ACL injury. Knee Surg Sports Traumatol Arthrosc. 2014; Epub ahead of print. PubMed doi:10.1007/s00167-014-3299-4 47. Beaulieu ML, Oh YK, Bedi A, Ashton-Miller JA, Wojtys EM. Does limited internal femoral rotation increase peak anterior cruciate ligament strain during a simulated pivot landing? Am J Sports Med. 2014;42(12)2955–2963. PubMed doi:10.1177/0363546514549446 48. Gomes JL, de Castro JV, Becker R. Decreased hip range of motion and noncontact injuries of the anterior cruciate ligament. Arthroscopy. 2008;24(9):1034–1037. PubMed doi:10.1016/j.arthro.2008.05.012 49. Ford KR, Myer GD, Hewett TE. Longitudinal effects of maturation on lower extremity joint stiffness in adolescent athletes. Am J Sports Med. 2010;38(9):1829–1837. PubMed doi:10.1177/0363546510367425
JAB Vol. 31, No. 4, 2015
ORIGINAL RESEARCH
Sex Differences During an Overhead Squat Assessment Timothy C. Mauntel,1 Eric G. Post,2 Darin A. Padua,1 and David R. Bell2 1University
of North Carolina; 2University of Wisconsin–Madison
A disparity exists between the rates of male and female lower extremity injuries. One factor that may contribute to this disparity is high-risk biomechanical patterns that are commonly displayed by females. It is unknown what biomechanical differences exist between males and females during an overhead squat. This study compared lower extremity biomechanics during an overhead squat and ranges of motion between males and females. An electromagnetic motion tracking system interfaced with a force platform was used to quantify peak lower extremity kinematics and kinetics during the descent phase of each squat. Range of motion measurements were assessed with a standard goniometer. Differences between male and female kinematics, kinetics, and ranges of motion were identified with t tests. Males displayed greater peak knee valgus angle, peak hip flexion angle, peak vertical ground reaction forces, and peak hip extension moments. Males also displayed less active ankle dorsiflexion with the knee extended and hip internal and external rotation than females. No other differences were observed. The biomechanical differences between males and females during the overhead squat may result from differences in lower extremity ranges of motion. Therefore, sex-specific injury prevention programs should be developed to improve biomechanics and ranges of motion. Keywords: biomechanics, kinematics, kinetics Lower extremity musculoskeletal injuries are the most significant medical issues affecting intercollegiate athletes1,2 and military personnel.3 Musculoskeletal injuries result in substantial medical costs, physical and mental anguish, and forced attrition from physical activity.1,4,5 Traumatic noncontact and overuse lower extremity injuries also carry long-term physical6,7 and financial consequences.8 The short- and long-term consequences of musculoskeletal injuries make it essential to identify risk factors associated with them. Two commonly proposed risk factors for lower extremity injuries include high-risk biomechanical patterns9–12 and sex.4,10,13–15 Collectively, these risk factors likely contribute significantly to the disparity seen in the rate of noncontact lower extremity injuries between males and females. Specifically, females have higher rates of lower extremity musculoskeletal injuries compared with their male counterparts.4,10,13–15 This issue is becoming increasingly apparent and problematic as the number of females participating in athletics4,16 and physically-demanding roles in the military17 continues to rise. It is likely that differences in lower extremity biomechanics between males and females influence the rates of noncontact injuries.13,18–20 It is therefore essential that biomechanical differences between the sexes are better understood so that sex-specific injury prevention programs can be developed and implemented.
Timothy C. Mauntel and Darin A. Padua are with the Department of Exercise and Sport Science, Sports Medicine Research Laboratory, University of North Carolina, Chapel Hill, NC. Eric G. Post is with the Department of Kinesiology, Wisconsin Injury in Sport Laboratory, University of Wisconsin–Madison, Madison, WI. David R. Bell is with the Department of Kinesiology and Department of Orthopedics and Rehabilitation, Wisconsin Injury in Sport Laboratory, University of Wisconsin–Madison, Madison, WI. Address author correspondence to Timothy C. Mauntel at tmauntel@ gmail.com. 244
High-risk biomechanical patterns result in irregular musculoskeletal stresses21 and increase the risk of sustaining noncontact and overuse lower extremity injuries.10,11,22 Females more commonly display these high-risk biomechanical patterns than do males.19,20,23–27 Commonly observed high-risk biomechanical patterns displayed by females, compared with males, during movement assessments include greater knee valgus angle,19,23 greater hip adduction angle,19 greater hip internal rotation motion,19,20 and less hip flexion motion.20,23 The differences in biomechanical patterns observed between males and females have been observed during single-leg squat assessments,19,27 jumping assessments,23–25 and cutting tasks.20,26 However, it is relatively unknown what differences, if any, exist between males and females during overhead squat assessments. Determining differences in male and female biomechanics during overhead squat assessments is important, as these assessments are commonly used in clinical28,29 and research settings.30–32 Furthermore, the overhead squat is similar to the single-leg squat in that it is slower than jumping and cutting assessments so it may be easier for clinicians to identify some of the aforementioned highrisk biomechanical patterns that can place individuals at increased risk of lower extremity injury.33 Range of motion measurements are important to consider when completing lower extremity biomechanical assessments, as they are related to high-risk biomechanical patterns.31,32,34 Range of motion measurements can aid clinicians in explaining biomechanical patterns observed during movement assessments. Understanding biomechanical and range of motion differences between males and females is important, because once these factors are understood clinicians can better plan and implement sex-specific injury prevention strategies. Specialized injury prevention programs can effectively reduce the rate of noncontact lower extremity injuries.35,36 Reducing the rate of musculoskeletal injuries will decrease the short- and long-term consequences of injury while increasing physical fitness and performance. Therefore, the purpose of this study was to determine if biomechanical differences exist between a population of physically
Sex Differences During an Overhead Squat 245
active males and females during an overhead squat assessment. This population is representative of physically active individuals in general as well as those that may be entering military basic training. We hypothesized females would display biomechanical patterns that are known to increase the risk of noncontact lower extremity injuries, while males would not. Generally, we hypothesized that females would have greater frontal plane hip and knee motion and less sagittal plane hip and trunk motion compared with males. Secondarily, range of motion measurements were assessed to provide further explanations of biomechanical differences observed between males and females. We hypothesized that females would have greater ankle dorsiflexion, hip internal rotation, and hip abduction, and less hip external rotation compared with males.
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Methods The study sample was a subset of individuals from a larger previously-reported sample.37 Stiffler et al37 recruited 100 recreationally active individuals (males = 30, females = 70) from the general university population. All participants scored ≥ 4 on the Tegner Activity Level survey38 and self-reported to be in good physical condition. Individuals were excluded if they reported current symptoms of injury to the lower extremity or low back, had an injury to the lower extremity or low back within the past 6 months that resulted in 3 or more consecutive days of missed activity, or had a previous surgical operation to the lower extremity or low back. Persons with known neurologic conditions were also excluded. This study was approved by the university’s institutional review board and each participant signed an informed consent form approved by the institutional review board.
Sample Subset Identification Following the initial data collection and reduction,37 a subset of 60 individuals (males = 30, females = 30) was identified; female participants were matched to male participants based on Tegner score (primary) and body mass index (BMI; secondary). Four male participants had missing data; these 4 males and their matched females were excluded from analyses. Six additional participants (males = 3, females = 3) were identified as being outliers (≥ 3 standard deviations away from the mean) for one or more outcome measures and, along with their matches, were also excluded from analyses. For one matched pair, the male participant was identified as an outlier for one variable and the female participant was identified as an outlier for a separate variable. A final sample size of 42 (males = 21, females = 21) was used for statistical analyses (Table 1).
Data Collection Procedures Following informed consent, demographic information (height [cm], mass [kg], age [y], leg dominance [the leg used to kick a soccer ball for maximal distance], and physical activity level) was collected for each participant. Participants wore their own t-shirt, shorts, and athletic shoes during data collection. Biomechanical and range of motion measures were completed on each participant’s dominant limb. The biomechanical and range of motion data collection procedures are identical to those previously reported.37
Biomechanical Data Collection Biomechanical data collection consisted of 5 overhead squats completed in succession. For the overhead squats, all participants started in a standardized position with their feet shoulder-width apart, toes pointed forward, heels on the floor, and arms extended overhead. Participants were instructed to squat in a deep, slow, and controlled manner, to a depth that was comfortable. A trial was deemed successful if the participant: (1) maintained the head facing forward; (2) kept the arms extended overhead; (3) kept the heels on the floor; (4) completed the assessment at the appropriate speed; and (5) completed the assessment in a fluid motion.30 An electromagnetic tracking system (Ascension Technologies, Inc., Burlington, VT) controlled by MotionMonitor software (Innovative Sports Training, Inc., Chicago, IL) was used in conjunction with a nonconductive force platform (Bertec Corporation, Columbus, OH) to quantify lower extremity three-dimensional kinematics and kinetics of the dominant limb during the overhead squat. Electromagnetic sensors were placed over the C7 spinous process, sacrum, lateral aspect of the thigh, and the anteromedial aspect of the proximal tibia and secured with double-sided tape, prewrap, and athletic tape. A segment-linkage model of the pelvis and dominant lower extremity was generated by digitizing the T12/L1 joint, the anterior superior iliac spines, femoral epicondyles, and malleoli. The location of the hip joint center was approximated using the Bell method.39 The knee joint center was defined as the midpoint of the femoral epicondyles and the ankle joint center was defined as the midpoint of the malleoli. Kinematic and kinetic data were sampled at 144 Hz and 1440 Hz, respectively. A right-handed global reference system was defined with the positive x-axis in the anterior direction, the positive y-axis to the left of each participant, and the positive z-axis in the superior direction. Euler angles were used with orders of rotation: Y (flexion/extension), X (abduction/adduction), and Z (internal/external rotation). Motion about the hip was defined as the thigh relative to the pelvis, and motion about the knee as the shank relative to the
Table 1 Subject demographics presented as means ± standard deviation and 95% confidence intervals Males
Females
Mean (95% CI)
Mean (95% CI)
P-value
182.56 ± 6.67 (179.71, 185.41)
166.92 ± 3.99 (165.22, 168.63)
< .001
Mass*
80.47 ± 6.93 (77.50, 83.43)
67.14 ± 7.18 (64.07, 70.21)
< .001
Age
20.29 ± 1.59 (19.61, 20.97)
20.19 ± 0.98 (19.77, 20.61)
.816
6.05 ± 1.20 (5.54, 6.56)
6.05 ± 1.20 (5.54, 6.56)
1.000
24.16 ± 1.98 (23.21, 25.01)
24.05 ± 1.95 (23.22, 24.88)
.858
Height*
Tegner score Body mass index
*Indicates significance at α ≤ .05. JAB Vol. 31, No. 4, 2015
246 Mauntel et al
thigh. Trunk motion was calculated relative to the global reference frame. Full extension of the hip, knee, and trunk were defined as 0° when the individual was standing in an erect, neutral position. Custom Matlab (Version 2013a, The MathWorks, Natick, MA) software was used to filter (fourth-order low-pass Butterworth filter with a cutoff frequency of 14.5 Hz) and identify the peak values of the dependent variables of interest during the “descent phase” of each squat. The descent phase was defined as the time from the start of knee flexion motion to the point of greatest knee flexion. Inverse dynamics was used to calculate net internal joint moments (N∙m) during the squat; internal joint moments were normalized to a product of body height (m) and body mass (kg). Ground reaction forces were normalized to body mass (kg). Peak kinematic and kinetic variables were averaged across the 5 overhead squat trials for each participant.
the axis was placed over the dominant limb anterior superior iliac spine, and the movement arm was placed along the midline of the anterior thigh. The dominant limb was passively abducted until the contralateral anterior superior iliac spine moved inferiorly.
Statistical Analyses Independent samples t tests (PASW Statistics for Windows version 21.0, IBM, Inc., Chicago, IL) were used to compare males and females. Averaged peak sagittal, frontal, and transverse plane knee, hip, and trunk joint angles, as well as averaged normalized peak vertical ground reaction forces and net internal joint moments, were compared between groups. Average joint range of motion values were also compared. Statistical significance was set a priori at α ≤ .05.
Results
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Range of Motion Data Collection Lower extremity range of motion was assessed with a standard 12-in goniometer. Three measurements were taken for each motion assessed. The 3 independent trials were averaged and the average value was used for statistical analyses. Study participants were supine for all range of motion assessments. The following procedures were used to assess ankle dorsiflexion, hip internal and external rotation, and hip abduction:32 Ankle Active and Passive Dorsiflexion. Ankle dorsiflexion was
measured with the knee extended and flexed to approximately 30°. The stationary arm of the goniometer was placed along the length of the lateral fibula, the axis was positioned over the lateral malleolus, and the movement arm was placed parallel to the lateral aspect of the fifth metatarsal. The dominant limb foot was actively and passively dorsiflexed until the end range was determined.
Hip Internal and External Rotation. The dominant limb was flexed to 90° at the hip and knee and the hip was in neutral alignment relative to the pelvis. The stationary arm of the goniometer was placed parallel to the table, the axis was placed over the center of the patella, and the movement arm was placed along the midline of the anterior shank. The dominant limb hip was passively internally and externally rotated until the end range was determined. Hip Abduction. The dominant limb was fully extended on the table. The stationary arm of the goniometer was placed along a line connecting the right and left anterior superior iliac spines,
For descriptive statistics, males were taller and heavier than the matched females (Table 1). No differences were observed for activity level or BMI since these variables were used as matching criteria. Significant differences were observed between groups for peak knee valgus angle, peak hip flexion angle, normalized peak vertical ground reaction forces, and normalized peak hip extension moment. There were no significant differences between groups for peak knee flexion or internal rotation angles, peak hip adduction or internal rotation angles, or peak trunk forward or lateral flexion angles. Significant differences were also not observed for normalized peak knee extension, knee valgus, knee internal rotation, or hip adduction moments (Tables 2 and 3). Significant differences also existed between males and females for active ankle dorsiflexion with the knee extended and hip internal and external rotation. There were no significant differences for active ankle dorsiflexion with the knee flexed, passive ankle dorsiflexion with the knee extended or flexed, or hip abduction (Table 4).
Discussion The overhead squat is a common functional movement assessment used to identify individuals displaying high-risk biomechanical patterns that may place them at greater risk of injury.28–32 The results of our study show that the overhead squat can be used to discriminate biomechanical differences between males and females. These bio-
Table 2 Peak joint angles presented as means ± standard deviation and 95% confidence intervals Males
Females
Mean (95% CI)
Mean (95% CI)
P-value
Knee flexion
110.26 ± 19.24 (102.03, 118.49)
100.64 ± 14.79 (94.31, 106.97)
.077
Knee valgus*
–12.62 ± 11.00 (–17.32, –7.92)
–4.86 ± 4.12 (–6.62, –3.12)
.004
4.20 ± 6.24 (1.53, 6.87)
4.64 ± 7.51 (1.43, 7.85)
.839
–117.02 ± 9.88 (–121.25, –112.79)
–105.19 ± 13.69 (–111.05, –99.33)
.003
Knee internal rotation Hip flexion* Hip adduction
6.89 ± 8.16 (3.40, 10.38)
5.31 ± 5.30 (3.04, 7.58)
.463
Hip internal rotation
13.42 ± 6.67 (10.57, 16.27)
10.71 ± 7.08 (7.68, 13.74)
.208
Trunk flexion
21.33 ± 13.30 (15.64, 27.02)
24.73 ± 16.49 (17.68, 31.78)
.467
4.14 ± 4.82 (2.08, 6.20)
3.79 ± 5.13 (1.60, 5.98)
.818
Trunk lateral flexion *Indicates significance at α ≤ .05.
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Sex Differences During an Overhead Squat 247
Table 3 Peak normalized ground reaction forces and internal joint moments presented as means ± standard deviation and 95% confidence intervals Males
Females
Mean (95% CI)
Mean (95% CI)
P-value
0.67 ± 0.07 (0.63, 0.70)
0.62 ± 0.06 (0.60, 0.64)
.027
Knee extension moment
–0.12 ± 0.03 (–0.13, –0.11)
–0.11 ± 0.02 (–0.12, –0.10)
.273
Knee valgus moment
–0.02 ± 0.01 (–0.02, –0.01)
–0.02 ± 0.01 (–0.02, –0.01)
.599
Knee internal rotation moment
0.02 ± 0.01 (0.01, 0.02)
0.01 ± 0.01 (0.01, 0.02)
.484
Hip extension moment*
0.12 ± 0.04 (0.11, 0.14)
0.09 ± 0.02 (0.08, 0.10)
< .001
Hip adduction moment
0.03 ± 0.02 (0.02, 0.03)
0.02 ± 0.01 (0.01, 0.03)
.224
Vertical ground reaction force*
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*Indicates significance at α ≤ .05. Note. Ground reaction forces were normalized to body mass (kg) and internal joint moments were normalized to a product of body height (m) and body mass (kg).
Table 4 Range of motion measurements presented as means ± standard deviation and 95% confidence intervals Males
Females
Mean (95% CI)
Mean (95% CI)
Active ankle dorsiflexion—knee extended*
0.24 ± 5.96 (–1.57, 2.04)
3.79 ± 5.27 (2.20, 5.39)
.047
Active ankle dorsiflexion—knee flexed
6.48 ± 6.66 (4.46, 8.49)
8.13 ± 6.67 (6.11, 10.15)
.427
Passive ankle dorsiflexion—knee extended
7.29 ± 5.97 (5.48, 9.09)
9.82 ± 6.07 (7.99, 11.66)
.179
Passive ankle dorsiflexion knee flexed
12.11 ± 7.45 (9.86, 14.36)
13.35 ± 8.10 (10.90, 15.80)
.609
Hip external rotation*
36.92 ± 11.61 (33.41, 40.43)
46.19 ± 14.70 (41.75, 50.64)
.029
Hip internal rotation*
28.78 ± 11.45 (25.05, 31.97)
37.51 ± 10.76 (34.25, 40.76)
.015
Hip abduction
32.84 ± 6.62 (30.84, 34.84)
36.93 ± 8.65 (35.32, 39.55)
.093
P-value
*Indicates significance at α ≤ .05.
mechanical differences are likely influenced in part by the differences observed in lower extremity ranges of motion. Biomechanical and range of motion differences between males and females may also help to explain the discrepancies observed between male and female noncontact lower extremity injury rates.4,13–15 Males displayed greater peak knee valgus angles (males = –12.62 ± 11.00°, females = –4.86 ± 4.12°) and greater peak hip flexion angles (males = –117.02 ± 9.88°, females = –105.19 ± 13.69°) than the females. These findings only partially support our hypothesis. The greater average peak knee valgus angle displayed by males does not support our hypothesis, as a greater peak valgus angle has been identified as a risk factor for noncontact lower extremity injuries.10,11,40–42 However, the greater hip flexion angles displayed by males does support our hypothesis since greater sagittal plane hip and knee motion is suggested as a protective mechanism for noncontact lower extremity injuries.24,43,44
Medial knee displacement is a visually observed movement pattern that is commonly used as a proxy for knee valgus motion.30,33,34 Previous research has shown that individuals who display medial knee displacement during a single-leg squat also display greater knee valgus motion, compared with individuals who maintain a neutral knee alignment.33 Furthermore, previous research has established a link between medial knee displacement during movement assessments and limited ankle dorsiflexion.31,32,34,37 Our current study found similar results. Male participants displayed greater knee valgus angles and less active ankle dorsiflexion with the knee extended (0.24 ± 5.96°) compared with females (3.79 ± 5.27°). Restricted ankle dorsiflexion could inhibit the tibia from moving forward over the foot and result in compensatory motions, including increased foot pronation, talar eversion, and tibial internal rotation.45 Ultimately, these compensatory foot and ankle motions could result in greater frontal and transverse plane motions at the hip and knee.34 These compensatory foot and ankle motions, in combination with the greater hip and knee sagittal plane motion, may have contributed to the greater valgus angles displayed by the males. Overall, males displayed less hip mobility than females. Specifically, males displayed less hip internal and external rotation. Limited transverse plane hip mobility, especially limited internal rotation motion, has been shown to increase an individual’s risk of noncontact anterior cruciate ligament injury.46–48 Gomes et al48 also showed that individuals with a restricted total arc of hip rotation were at increased risk of sustaining a noncontact knee injury. It has been suggested that similar to how restricted ankle mobility can alter proximal joint angles (ie, the knee),34 restricted hip mobility can alter distal joint angles (ie, the knee) during functional tasks.46 Furthermore, while not significantly different between the sexes, males displayed ~4° less hip abduction motion than females (P = .093). This finding is similar to one previously reported by Mauntel et al,34 who compared range of motion differences between individuals who displayed medial knee displacement during a singleleg squat and those who did not. The combination of restricted hip ranges of motion and limited active ankle dorsiflexion displayed by the males likely contributed to the greater frontal plane knee motion (ie, valgus) we observed. Males have been shown to display greater sagittal plane hip motion during movement assessments compared with females.19,20,26 However, males have not displayed greater sagittal plane hip motion compared with females during all movement assessments.23,26,27 Kernozek et al23 found that females displayed a 14° more peak hip
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248 Mauntel et al
flexion angle compared with males during a drop-landing task. One potential explanation for the difference observed in peak hip flexion angle between the previous research23 and our study is static stance posture. In our study the male participants displayed greater minimum hip flexion angles (–8.31 ± 6.34°) compared with females (–3.89 ± 6.40°), which disagrees with previous research23 that observed females had greater hip flexion angles in a static position. Our study and the work of others23,26 suggest that resting joint positions are important to consider when evaluating movement assessments. Males also had greater normalized peak vertical ground reaction forces (males = 0.67 ± 0.07, females = 0.62 ± 0.06) and normalized peak hip extension moments (males = 0.12 ± 0.04, females = 0.09 ± 0.02) than the females. Our finding of males displaying greater normalized peak internal hip extension moments is similar to what has been previously reported during cutting20 and jumping49 tasks. Males may display greater hip extension moments because of greater passive restraints resulting from greater sagittal plane stiffness49 and restrictions in hip ranges of motion, as observed in our study, compared with females. However, the exact mechanism for why males display greater peak internal hip extension moments during a variety of dynamic tasks remains unknown. The major limitation of this study is that only one movement assessment was examined. Additional differences in biomechanics may have been identified between sexes had additional movement assessments been used. In addition, biomechanical data were not collected from the foot and additional differences in lower extremity biomechanics may have been observed had these data been collected. Furthermore, the capability of the biomechanical and range of motion differences observed between sexes to predict future injury was also not assessed in this study. Determining the ability of these differences to discriminate between individuals who go on to sustain an injury and those who do not should be determined. The overhead squat assessment is commonly used by sports medicine professionals to identify individuals who display biomechanical patterns that may place them at greater risk of lower extremity injury.28–32 The overhead squat has the ability to identify biomechanical differences between males and females; however, it has yet to be determined if these biomechanical differences are clinically meaningful. Until the overhead squat is more formally developed into a movement assessment capable of identifying lower extremity injury risk factors, clinicians should continue to use multiple movement assessments to develop an accurate profile of an individual’s movement patterns. Acknowledgments This research was supported by the Virginia Horne Henry Fund for Women’s Physical Education.
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