Influence of Thigh and Shank Lengths and Ratios on Kinematic and Kinetic Characteristics of the Knee Joint During Barbell Back Squat

Abstract

The barbell back squat, a prevalent lower-limb resistance exercise characterized by a closed kinetic chain and multi-joint movement, results in the greatest knee joint range of motion. Variations in thigh and shank lengths and their ratios may influence knee joint mechanics. This study investigated the effects of thigh and shank lengths and their ratios on knee kinematics and kinetics during the barbell back squat. Fifty resistance-trained adult men participated. Kinematic and kinetic data were collected using an eight-camera motion capture system and two force plates. Correlation and simple linear regression analyses were conducted to evaluate the relationships between thigh and shank length parameters and knee joint mechanics. Greater thigh length was significantly associated with increased anterior knee displacement and knee extension moment. Additionally, longer shank length and a higher shank-to-thigh ratio were associated with greater knee abduction and internal rotation angles. Consequently, increased thigh length may contribute to greater anterior knee displacement, while increased shank length may be associated with increased knee abduction and internal rotation. Accordingly, trainers and trainees should evaluate individual thigh and shank lengths. For participants with relatively longer shank and thigh segments, compensatory knee movements should be closely monitored to mitigate the risk of musculoskeletal injuries.

1. Introduction

The barbell back squat is one of the most widely practiced squat variations, primarily focusing on improving core stability and lower-extremity muscle function [1,2,3]. This exercise involves placing a weighted barbell across the upper trapezius while keeping both feet fixed on the ground and executing repeated flexion and extension movements of the lower-limb joints to move the combined load of the body and barbell along a vertical axis [4]. Due to these mechanical characteristics, the barbell back squat is classified as a closed kinetic chain, multi-joint exercise [5,6] and is widely recommended not only for enhancing athletic performance, but also for musculoskeletal injury prevention and rehabilitation [7,8].

Safe and effective squat performance requires both core stability and adequate mobility across the lower-extremity joints [9]. In particular, the knee demands the greatest range of motion (ROM) in the sagittal plane, and ensuring stability at the knee involves not only achieving proper flexion and extension but also minimizing unwanted movements in the frontal and transverse planes [10,11,12]. However, compensatory movements that disrupt knee alignment are frequently observed during the barbell back squat, which may increase the risk of knee injury [9,13].

One of the most common compensatory patterns observed during the barbell back squat is knee valgus, characterized by medial collapse of the knees due to knee abduction and internal tibial rotation [9,14,15]. This movement pattern is considered a major risk factor for non-contact anterior cruciate ligament (ACL) injuries [16,17]. Since the barbell back squat involves a closed kinetic chain and requires coordinated movement across multiple joints, knee alignment and ROM are affected by segmental interactions within the lower limbs as well as the functional capacity of the surrounding musculature [9,15,18,19]. Compensatory movement at the knee may arise from various factors, including excessive loading, muscular weakness, restricted joint mobility, and individual anatomical structure. Notably, anatomical factors, such as segment lengths (e.g., trunk, thigh, shank), Q-angle, and pelvic width [20,21,22,23,24], are relatively fixed and not easily modified through training or therapeutic intervention. Consequently, anatomical characteristics are predisposing factors that should be considered to mitigate the risk of knee injury during the barbell back squat.

Previous research has explored the influence of anatomical structure on joint mobility, alignment, and movement performance during squatting tasks [21,22,23,25]. Specifically, thigh and shank lengths are regarded as critical anthropometric variables, because knee joint motion during the barbell back squat is regulated by the articulatory interaction of the thigh and shank [21]. Given that the knee joint demonstrates the greatest ROM during the barbell back squat and serves as a primary site of mechanical loading, the absolute lengths and relative proportions of the thigh and shank may substantially affect joint displacement patterns, mechanical loading, and compensatory movements. However, existing studies have predominantly focused on the relationship between segment lengths and lower-limb joint ROM [23], or the impact of segment length on inter-joint coordination [22]. In contrast, there is a paucity of studies quantitatively examining the effects of thigh and shank lengths and their ratios on the kinematic and kinetic characteristics of the knee joint, as well as their association with knee injury risk during the barbell back squat.

Consequently, the present study aimed to investigate the effects of thigh and shank lengths and their ratios on the kinematic and kinetic characteristics of the knee joint during the barbell back squat. The findings are intended to serve as foundational data for developing safer and more effective barbell back squat techniques tailored to individual anthropometric differences. The following hypotheses were proposed: (1) thigh and shank lengths will significantly affect peak knee joint angles and maximal displacement in the anterior–posterior and medial–lateral directions during the barbell back squat, and (2) thigh and shank lengths will significantly affect peak moments and reaction forces at the knee during the barbell back squat.

2. Materials and Methods

2.1. Participants

The sample size was determined through power analysis using G*Power 3.1.9.7 software (Franz Faul, Kiel, Germany) with effect size f²: 0.25, alpha level: 0.05, and power: 0.8. The minimum sample size was calculated to be 28 cases [26]. Based on this, a total of 50 adult men were recruited for the study. Eligibility criteria included no history of musculoskeletal injuries in the lower extremities or postural asymmetry within the past year, right-leg dominance, and a minimum of one year of consistent barbell back squat training at moderate or higher intensity at least three times per week (

Table 1. Characteristics of participants.

Variables (Unit)	Participants (n = 50)
	Age (y)	Height (cm)	Weight (kg)	SQ 1-RM Weight (kg)
Mean ± SD	23.88 ± 4.49	175.69 ± 4.76	73.95 ± 7.77	109.78 ± 16.12

Abbreviations: SQ, squat; 1-RM, one-repetition maximum.

). The Institutional Review Board of Konkuk University approved the study before participant recruitment and data collection (IRB No. 7001355-201706-HR-184).

2.2. Procedures

Participants were informed of the purpose and procedures of the study, and only those who provided consent were permitted to participate. One week prior to testing, each participant’s one-repetition maximum (1-RM) test for the barbell back squat was directly measured in accordance with the National Strength and Conditioning Association protocol [27]. The 1-RM value was utilized to determine the squat load in the main experiment.

Prior to data collection, the global reference frame and spatial coordinates of the laboratory were calibrated using the Active Wand (Vicon Motion Systems Ltd., Oxford, UK), with the y-axis defined as anterior–posterior, x-axis as medial–lateral, and z-axis as vertical.

Participants wore spandex clothing and completed a 10 min warm-up, including stretching, to avoid injury. A trained examiner measured thigh and shank lengths three times using a tape measure. Following measurement, 47 reflective markers (diameter: 15 mm) were attached to key anatomical landmarks based on Vicon’s Plug-in-Gait Model [28]. Three-dimensional position data of the markers were captured using eight infrared motion capture cameras (MX-T10S, Vicon, Hauppauge, NY, USA; 250 Hz). A static trial was recorded in the anatomical position for approximately 3 s, followed by dynamic trials of the barbell back squat. During the dynamic trial, each participant performed three repetitions, considering neuromuscular fatigue.

2.3. Barbell Back Squat Exercise

Participants stood on two force plates with feet spaced at 100–120% of pelvic width and externally rotated 15–30°. A standard Olympic barbell (length: 2200 mm, mass: 20 kg) was positioned between the spinous process of C7 and the scapular spine. Squats were performed at approximately 50% of 1-RM, corresponding to low-to-moderate intensity (<60% of 1-RM), a range commonly employed for muscular endurance training. High loads were avoided to minimize fatigue and reduce compensatory joint movements [22].

Participants performed deep squats with the posterior thigh contacting the calf, achieving knee flexion angles ≥ 120° [10]. Each participant completed three repetitions. To ensure consistency, squat tempo and depth were practiced during the warm-up, and a metronome was used to control movement speed during trials.

2.4. Thigh and Shank Length Variables

Thigh and shank lengths were measured three times by a single experienced examiner using a tape measure. As all participants were right-leg dominant and exhibited no observable left–right asymmetry, measurements were taken from the right leg. Thigh length was defined as the distance from the greater trochanter to the lateral epicondyle of the femur, and shank length as the distance from the lateral epicondyle to the lateral malleolus [21,23]. To ensure measurement accuracy, anatomical landmarks—the greater trochanter, lateral epicondyle, and lateral malleolus—were first palpated and marked with stickers (Figure 1).

The three repeated measurements for each variable were used to calculate the intraclass correlation coefficient (ICC) to verify intra-rater reliability. The three measurements were averaged for both thigh and shank lengths and used for data analysis. The shank-to-thigh length ratio (STLR) was calculated as the percentage of shank length relative to the thigh length, based on the averaged values. A STLR of 100% indicates equal lengths of the shank and thigh; values below 100% indicate a shorter shank relative to the thigh; and a value exceeding 100% signifies a longer shank compared to the thigh. For this study, thigh length, shank length, and STLR were selected as the study parameters. The formula for STLR is shown below:

$$Shank/Thigh Length Ratio (STLR)={\displaystyle \frac{Shank Length}{Thigh Length}}\times 100$$

2.5. Data Processing

During the barbell back squat, positional data from reflective markers affixed to major body segments and joints along with ground reaction force data were synchronized using eight infrared motion capture cameras and two force plates via Giganet (Vicon Motion Systems Ltd., Oxford, UK). Raw data were collected and converted into C3D files using Nexus software (ver. 2.14, Vicon Inc., Hauppauge, NY, USA).

Each participant’s static and dynamic C3D files were imported into Visual3D (Version 6, C-Motion Inc., Germantown, MD, USA). To remove noise, marker trajectory data were filtered using a second-order Butterworth low-pass filter at 6 Hz. Ground reaction force data were similarly filtered using a second-order Butterworth low-pass filter at 50 Hz.

To examine the impact of thigh and shank length variables on knee joint kinematics and kinetics, three events were defined: Ready (initial squat position), Maximal Knee Flexion (MKF) (point of maximum knee flexion), and Finish (completion of the squat movement). Kinematic and kinetic variables of the knee joint were calculated throughout the entire phase from Ready to Finish.

Local coordinate systems were established for the thigh and shank segments. The x-axis represented the medial–lateral direction, the y-axis anterior–posterior, and the z-axis vertical. Kinematic variables included joint peak angles and peak displacement in the anterior–posterior and medial–lateral directions. Peak joint angles were calculated using the Cardan orientation method, based on the angle of the shank segment relative to that of the thigh segment. Peak joint angles for each direction were defined as follows: for the x-axis, positive values indicate extension and negative values indicate flexion; for the y-axis, positive values indicate adduction and negative values indicate abduction; and for the z-axis, positive values indicate internal rotation and negative values indicate external rotation. These definitions describe the movement of the shank (tibia) relative to the thigh (femur).

Peak displacement of the knee joint in the horizontal plane was calculated based on reflective markers placed on the lateral sides of the knee and ankle joints. As the feet remain fixed on the ground during the barbell back squat, displacement was derived by measuring the maximum displacement of the position of the lateral knee marker relative to those of the lateral ankle marker in the anterior–posterior and medial–lateral directions.

Kinetic variables included joint peak moments and peak forces. Peak moments of the knee joint were defined as follows: for the x-axis, positive values indicate extension and negative values flexion; for the y-axis, positive values indicate adduction and negative values abduction; for the z-axis, positive values indicate internal rotation and negative values external rotation. Peak forces of the knee joint were defined as follows: for the x-axis, positive values indicate medial shear force and negative values lateral shear force; for the y-axis, positive values indicate anterior shear force and negative values posterior shear force; and for the z-axis, negative values indicate compressive force. Both peak moments and peak forces were normalized by dividing by the sum of each participant’s body weight and the external load.

2.6. Statistical Analysis

Intra-rater reliability was assessed by calculating the intraclass correlation coefficients (ICCs) based on the three repeated measurements of thigh and shank lengths obtained by the same examiner. The mean of the three values was used for all subsequent analyses.

The relationship between thigh and shank lengths, STLR, and the kinematic and kinetic characteristics of the knee joint during the barbell back squat were analyzed by first conducting Pearson’s correlation analysis, followed by simple regression analysis for variables exhibiting statistically significant associations. All statistical procedures were conducted using SPSS version 27.0 (IBM Corp., Armonk, NY, USA), with the significance level set at α = 0.05.

3. Results

3.1. Thigh and Shank Length Measurements and Reliability

Thigh and shank lengths were measured three times for each participant, and intra-rater reliability was assessed using ICCs (

Table 2. Intra-rater reliability of thigh and shank length measurements.

Variables (Unit)	Mean ± SD	ICC (2,1)	95% CI	p-Value
Thigh Length (cm)	42.4 ± 2.5	0.996	0.993–0.997	<0.001
Shank Length (cm)	39.6 ± 2.1	0.993	0.989–0.996	<0.001
STLR (%)	93.7 ± 7.1	-	-	-

Abbreviations: SD, standard deviation; STLR, shank/thigh length ratio.

). The results revealed excellent reliability for both variables, with ICC = 0.996 for thigh length and ICC = 0.993 for shank length (p < 0.001).

3.2. Kinematic and Kinetic Variables of the Knee Joint During the Barbell Back Squat

To examine the effect of thigh and shank lengths on knee joint mechanics during the barbell back squat, the following variables were calculated for kinematics: peak joint angles in each direction and maximal displacement in the anterior–posterior and medial–lateral directions (

Table 3. Knee joint kinematic variables in each direction during the barbell back squat.

Variables (Unit)	Direction	Mean ± SD
Knee Joint Peak Angle (°)	Flexion (−)/Extension (+)	−130.03 ± 8.37
	Abduction (−)/Adduction (+)	4.35 ± 8.05
	ER (−)/IR (+)	13.45 ± 11.63
Knee Joint Peak Displacement (cm)	Anterior (+)/Posterior (−)	17.25 ± 3.43
	Medial (−)/Lateral (+)	8.87 ± 2.78

Abbreviations: ER, external rotation; IR, internal rotation.

); and, for kinetics, peak moments and peak forces in each direction (

Table 4. Knee joint kinetic variables in each direction during the barbell back squat.

Variables (Unit)	Direction	Mean ± SD
Knee Joint Peak Moment (N/kg)	Flexion (−)/Extension (+)	0.72 ± 0.28
	Abduction (−)/Adduction (+)	−0.48 ± 0.15
	ER (−)/IR (+)	−0.11 ± 0.05
Knee Joint Peak Force (N/kg)	Anterior (+)/Posterior (−) Shear Force	−0.09 ± 0.40
	Medial (+)/Lateral (−) Shear Force	−0.21 ± 0.08
	Compressive Force (−)	−5.76 ± 0.51

Abbreviations: ER, external rotation; IR, internal rotation.

).

3.3. Correlation Between Thigh and Shank Length Variables and Knee Joint Kinematic and Kinetic Variables

The relationships between the thigh and shank length variables and the kinematic and kinetic characteristics of the knee joint during the barbell back squat were examined using correlation analysis (

Table 5. Correlation analysis between thigh and shank length variables and kinematic and kinetic variables of the knee joint.

Variables		Thigh–Shank Length Variables
		Thigh Length		Shank Length		STLR
		r	p-Value	r	p-Value	r	p-Value
Joint Peak Angle	Flexion	−0.147	0.307	−0.050	0.730	0.066	0.647
	Adduction	−0.016	0.913	−0.555 ***	<0.001	−0.385 **	0.006
	IR	−0.250	0.080	0.327 *	0.020	0.426 **	0.002
Peak Displacement	Anterior	0.537 ***	<0.001	0.215	0.134	−0.262	0.066
	Medial	−0.093	0.520	−0.104	0.473	0.005	0.975
Joint Peak Moment	Extension	0.389 **	0.005	−0.118	0.413	−0.390 **	0.005
	Abduction	0.095	0.510	0.049	0.736	−0.034	0.816
	ER	−0.138	0.339	0.005	0.974	0.114	0.432
Joint Peak Force	Posterior	0.172	0.231	−0.059	0.686	−0.182	0.207
	Lateral	0.204	0.155	0.236	0.099	0.016	0.913
	Compressive	0.186	0.195	0.243	0.090	0.040	0.783

Abbreviations: ER, external rotation; IR, internal rotation; STLR, shank/thigh length ratio; * p < 0.05, ** p < 0.01, *** p < 0.001.

). A positive correlation was found between thigh length and anterior displacement of the knee joint (r = 0.537, p < 0.001), as well as between thigh length and the joint peak extension moment (r = 0.387, p = 0.005). Shank length was negatively correlated with the knee joint peak adduction angle (r = –0.555, p < 0.001) and positively correlated with the knee joint peak internal rotation angle (r = 0.327, p = 0.020). STLR was negatively correlated with the knee joint peak adduction angle (r = –0.385, p = 0.006) and the joint peak extension moment (r = –0.390, p = 0.005) and positively correlated with the knee joint peak internal rotation angle (r = 0.426, p = 0.002).

3.4. Simple Regression Analysis Between Thigh and Shank Length Variables and Knee Joint Kinematic and Kinetic Variables

The effects of the thigh and shank length variables on the kinematic and kinetic characteristics of the knee joint during the barbell back squat were analyzed using simple regression analysis with variable pairs that exhibited statistically significant correlations (

Table 6. Results of simple regression analysis between thigh and shank length variables and the kinematic and kinetic variables of the knee joint.

Independent Variable	Dependent Variable	Unstandardized Coefficients		Standardized Coefficients	t	p-Value	95% CI
		B	Std. Error	Beta			Lower Bound	Upper Bound
Thigh Length	(Constant)	−13.884	7.062		−1.966	0.055	−28.083	0.314
	Peak AP Displacement	0.734	0.166	0.537	4.416	<0.001 ***	0.400	1.068
	(Constant)	−1.096	0.621		−1.766	0.084	−2.344	0.152
	Peak Extension Moment	0.043	0.015	0.389	2.926	0.005 **	0.013	0.072
Shank Length	(Constant)	87.987	18.108		4.859	<0.001 ***	51.578	124.395
	Peak Adduction Angle	−2.111	0.456	−0.555	−4.625	<0.001 ***	−3.028	−1.193
	(Constant)	−57.768	29.748		−1.942	0.058	−117.580	2.044
	Peak IR Angle	1.797	0.750	0.327	2.397	0.020 *	0.290	3.305
STLR	(Constant)	45.065	14.109		3.194	0.002 **	16.697	73.432
	Peak Adduction Angle	−0.435	0.150	−0.385	−2.894	0.006 **	−0.737	−0.133
	(Constant)	−51.595	20.001		−2.580	0.013 *	−91.810	−11.379
	Peak IR Angle	0.694	0.213	0.426	3.261	0.002 **	0.266	1.122
	(Constant)	2.130	0.483		4.409	<0.001 ***	1.159	3.102
	Peak Extension Moment	−0.015	0.005	−0.390	−2.933	0.005 **	−0.025	−0.005

Abbreviations: STLR, shank/thigh length ratio; 95% CI, 95% confidence interval for B; * p < 0.05, ** p < 0.01, *** p < 0.001.

). Thigh length showed a statistically significant effect on anterior displacement of the knee joint (R² = 0.289, F = 19.5, p < 0.001) and peak extension moment (R² = 0.151, F = 8.563, p = 0.005). Shank length significantly affected the knee joint peak adduction angle (R² = 0.308, F = 21.392, p < 0.001) and peak internal rotation angle (R² = 0.107, F = 5.747, p = 0.020). STLR had significant effects on the knee joint peak adduction angle (R² = 0.149, F = 8.374, p = 0.006), peak internal rotation angle (R² = 0.181, F = 10.634, p = 0.002), and peak extension moment (R² = 0.152, F = 8.604, p = 0.005). The regression lines and equations illustrating the relationships between the thigh and shank length variables and the knee joint kinematic and kinetic variables are presented in Figure 2.

4. Discussion

This study measured thigh and shank lengths in 50 resistance-trained adult men and analyzed knee joint kinematic and kinetic variables during the barbell back squat using a motion capture system and force plates. Kinematic variables included peak joint angles and maximal displacement in the anterior–posterior and medial–lateral directions, while kinetic variables included peak moments and forces. Thigh and shank lengths, as well as their ratio, were measured three times by the same examiner, exhibiting excellent intra-rater reliability (ICC: thigh 0.996; shank 0.993) [29]. Average values were used for correlation and regression analyses. All participants performed the barbell back squat as a deep squat, defined as knee flexion beyond 120° [10,13], with an average peak flexion angle of –130.03° (Table 3), confirming adherence to this criterion. Given that the barbell back squat is a closed kinetic chain, multi-joint exercise involving the coordinated movement of the ankle, knee, and hip joints, structural differences in the femur and tibia may affect knee joint motion and loading [9,30,31]. Consequently, this study aimed to elucidate how thigh and shank lengths influence knee biomechanics, providing foundational evidence for safer and more effective squat performance tailored to individual segment lengths.

The results showed that thigh length was positively correlated with both anterior displacement of the knee joint and the joint peak extension moment. Regression analysis indicated that thigh length accounted for 28.9% of the variance in anterior displacement (Figure 2A) and 15.1% of the variance in joint peak extension moment (Figure 2B). These findings suggest that longer thigh length is associated with increased anterior displacement and higher extension moment at the knee joint. In contrast, the STLR was negatively associated with the joint peak extension moment, with an explanatory power of 15.2% (Figure 2G). This indicates that a relatively longer shank in proportion to the thigh results in a decrease in the joint peak extension moment. Collectively, the results suggest that greater thigh length leads to increased anterior displacement and extension moment at the knee during the barbell back squat.

An increase in thigh length during squat performance shifts the center of mass of the thigh and torso posteriorly. To compensate for this, the tibia moves anteriorly, resulting in anterior translation of the knee joint to maintain postural balance [23]. The findings of this study suggest a similar compensatory pattern, with longer thigh length contributing to increased anterior displacement of the knee joint. The joint peak extension moment is determined by the magnitude of the ground reaction force and the moment arm formed between the center of the knee joint and the ground reaction force vector in the sagittal plane. The increase in joint peak extension moment observed with greater thigh length may be explained by the anterior shift of the knee joint, which increases the length of the moment arm. This increased anterior displacement and joint peak extension moment may elevate patellofemoral joint pressure, increasing the risk of injury to surrounding ligaments and cartilage [11,18,32]. Therefore, individuals with relatively long thighs may be at greater risk for knee joint injury during the barbell back squat and should be advised to adjust their technique accordingly to prevent excessive loading.

The results of this study revealed that shank length was negatively correlated with the knee joint peak adduction angle and positively correlated with the peak internal rotation angle during the barbell back squat. Regression analysis revealed that shank length accounted for 30.8% of the variance in the peak adduction angle (Figure 2C), which was the highest explanatory power among the tested variables, and 10.7% of the variance in the peak internal rotation angle (Figure 2D). Regarding the regression line between shank length and peak adduction angle (Figure 2C), the adduction angle (positive value) gradually decreased and shifted toward abduction (negative value) with increasing shank length, indicating that individuals with longer shanks exhibited greater peak abduction at the knee joint. Additionally, peak internal rotation of the knee joint increased with greater shank length. A similar pattern was observed for the STLR. During the barbell back squat, STLR was significantly negatively correlated with knee joint peak adduction angles and significantly positively correlated with peak internal rotation angles. Regression analysis showed that STLR accounted for 14.9% of the variance in peak adduction angle (Figure 2F) and 18.1% in peak internal rotation angle (Figure 2F). Examination of the regression line revealed that as STLR increased—that is, as the shank became relatively longer than the thigh—both peak abduction and internal rotation angles at the knee joint tended to increase. This pattern was consistent with the results observed for absolute shank length, suggesting that increased STLR may contribute to compensatory movement patterns at the knee. All participants in this study performed deep squats, which require maximal ROM across the lower-limb joints. Participants with higher STLR may have experienced greater difficulty in reaching the deep flexion angles required by the movement. In attempting full-depth squats, these individuals may have relied not only on knee flexion and extension, but also on compensatory motions such as abduction and internal rotation.

Excessive abduction and internal rotation of the knee joint are well-documented non-contact risk factors for ACL injury [33,34]. Given that the barbell back squat involves both bodyweight and additional load, stress on the ACL may be further amplified. This study found that both increased shank length and STLR were associated with greater peak abduction and internal rotation angles at the knee, movement patterns that may increase the risk of ACL injury. Although the findings of this study demonstrated low statistical explanatory power, these movement patterns are expected to increase the risk of ACL injury and warrant caution. Therefore, individuals with high STLR should be carefully monitored for compensatory movement during squatting, and technique modifications may be required to minimize joint stress and reduce the risk of injury.

It is important to acknowledge that the present study was conducted exclusively among adult male participants with previous experience in resistance training and no history of musculoskeletal injuries. Consequently, the findings may not be generalizable to novice lifters, female participants, or older adults, who may exhibit differences in anatomical structure or motor control strategies. Additionally, the results may not be applicable under varying squat conditions, such as high loads and different foot positions and widths, squatting depths, or squatting velocities, compared to those employed in this study. Future research should expand on this study by considering a wider array of anthropometric variables, assessing their impact on lower-limb biomechanics and injury risk across diverse populations, including beginners, female participants, and older adults, as well as under various squat conditions.

5. Conclusions

Greater thigh length was significantly associated with increased anterior displacement and peak extension moment at the knee joint. In contrast, longer shank length and a higher STLR were associated with increased peak abduction and internal rotation angles. These results suggest that individuals with relatively long thighs or shanks are more likely to exhibit compensatory knee joint movements, such as anterior translation, abduction, and internal rotation, during the barbell back squat. Therefore, trainers and trainees should assess individual thigh and shank lengths before commencing training. For participants with relatively longer thigh and shank segments, it is imperative to closely monitor compensatory knee movements to mitigate the risk of musculoskeletal injuries to the knee joint during the execution of barbell back squats.