Physical Therapy Korea

Squats are widely recognized as effective exercises for strengthening the lower body by activating various lower-extremity muscles, including the gluteus maximus (Gmax). During squats, emphasis is placed on hip extension and external rotation, with the Gmax playing a critical role. Squats not only improve lower-limb strength but also enhance joint stability, balance, and functional movement, making them a cornerstone in both athletic training and rehabilitation programs. Consequently, squats have proven to be an effective method for enhancing and improving Gmax function [1].

As one of the largest muscles in the human body, the Gmax plays a pivotal role in providing stability and strength to the hip joint. This function directly impacts a variety of everyday activities, as well as athletic performance, including tasks such as walking, running, and jumping. A weak Gmax can lead to pelvic instability, lower back pain, hip problems, and other complications, making it an essential factor to consider in physical therapy and exercise prescriptions [2]. Despite its benefits, proper squat performance requires precise control of posture and joint alignment to maximize muscle activation and minimize injury risk. Variations in squat depth, ankle positioning, and weight distribution can significantly influence muscle engagement and joint loading, highlighting the importance of individualized training and rehabilitation approaches.

Dorsiflexion (DF) and plantarflexion (PF) of the ankle significantly alter the body’s center of mass and the path of force transmission, leading to distinct muscle activation patterns. For instance, PF shifts the center of mass forward, resulting in increased activation of knee extensors such as the vastus medialis oblique (VMO) and rectus femoris. Conversely, DF shifts the center of mass backward, enhancing the demand for hip extension and increasing activation of the Gmax. These positional adjustments allow targeted muscle engagement, optimizing rehabilitation and training outcomes [3].

Restricted ankle DF impedes the normal forward translation of the tibia over the talus, which is critical for maintaining proper sagittal plane mechanics during squatting movements. This restriction can lead to compensatory alterations in movement patterns, such as increased knee valgus, excessive forward trunk lean, or greater reliance on adjacent joints and muscles, such as the lumbar spine or hamstrings, to achieve the desired range of motion. Consequently, these compensatory strategies disrupt the coordinated activation of the lower limb muscles, reducing the engagement of the Gmax and other primary stabilizers, while increasing the risk of inefficient movement and overloading of secondary structures [4].

While numerous studies have investigated the mechanics of squats with a focus on the quadriceps and hamstrings, relatively few have explored the specific impact of ankle positions on Gmax activation. This gap highlights the need for research that integrates the effects of ankle alignment on muscle activation to optimize squat performance and exercise prescriptions.

The position of the ankle not only influences Gmax activation but also affects coordination patterns among other lower extremity muscles. Depending on the angle, the Gmax may become more active or other muscles may compensate for its reduced activation [3]. Understanding these interactions is crucial for designing more effective exercise programs.

Surface electromyography (sEMG) is an essential tool for analyzing muscle activation because it quantitatively evaluates muscle activity by measuring the electrical signals generated during muscle contraction. sEMG commonly uses the percentages of maximum voluntary isometric contraction (%MVIC) as an indicator, which reflects the muscle activation level as a percentage of its maximal capacity during specific exercises [5].

While most existing studies have focused on muscles such as the quadriceps and hamstrings, fewer have examined the Gmax. Research exploring the effect of ankle positions on Gmax activation during squats remain scarce despite the potential impact of ankle positioning on movement patterns and muscle activation.

This study aimed to assess the impact of three distinct ankle positions on Gmax activation by examining variations in muscle activation during squats. It was hypothesized that DF of the ankle would result in greater Gmax activation compared to PF or neutral (NEU) positions during squats. The findings may offer physical therapists and exercise professionals a foundation for designing more effective exercise programs.

1. Participants

The participants, comprising 30 healthy adults (26 males and 4 females) aged 18–30 years, were recruited from Wonju, Gangwon Province. Only those without a history of lower limb injuries or surgery were included.

The exclusion criteria were as follows: individuals with a history of ankle or lower limb injuries; those with ankle DF range of motion less than 20° in a flexed knee position, as assessed using a goniometer; those with neurological disorders; those experiencing pain in the ankle, lower limb, or lower back; and individuals who consumed coffee or alcohol the day prior to or on the day of the experiment.

This study was approved by the Institutional Review Board (IRB) of the Yonsei University Mirae campus (IRB no. 1041849-202407-BM-145-02). The participants’ characteristics are presented in Table 1.

Table 1 . General characteristics of the participants (N = 30).

Variable	Value
Age (y)	28.9 ± 0.4
Height (cm)	173.4 ± 1.2
Weight (kg)	75.0 ± 2.7
Body mass index (kg/m2)	24.9 ± 0.8

Values are presented as mean ± standard deviation..

2. Sample Size

The sample size was calculated using G*Power software (ver. 3.1.9.7), with an effect size of 0.25, an alpha error probability of 0.05, and a power (1-β) of 0.8. The required sample size was determined to be 28 participants, and a total of 35 participants were recruited to account for potential dropouts. During the study, five participants dropped out for various reasons, resulting in a final sample size of 30 participants.

3. Recruitment and Consent Procedures

Participants were recruited through public posts at Wonju city hall website community board and university bulletin boards. Only those who voluntarily consented to participate were included. After providing a thorough explanation of the research procedure, written consent was obtained from all participants.

4. Study Design

This study employed a repeated-measures design to assess changes in muscle activation during squat exercises at different ankle positions. sEMG was used to measure the muscle activation of the Gmax, VMO, vastus lateralis oblique (VLO), and biceps femoris (BF) (Figure 1).

Figure 1. Electrode placement (A) gluteus maximus, (B) vastus medialis oblique and vastus lateralis oblique, and (C) biceps femoris.

5. Experimental Procedures

Muscle activation was measured using specific postures to target each muscle group. For the Gmax, participants were positioned in a quadruped posture (on hands and knees) with their hips and knees bent at approximately 90°. In this position, one leg was lifted posteriorly while maintaining 90° knee flexion to ensure Gmax activation. Although the prone position traditionally recommended by Kendall et al. [5] typically provides more consistent activation patterns, the quadruped posture was selected based on preliminary testing, which indicated that it elicited higher Gmax activation levels in some individuals. This decision reflects the study’s aim to maximize Gmax engagement and obtain data more representative of peak activation potential, despite acknowledging the potential trade-off in activation consistency. To measure the VMO and VLO, participants were seated with their feet externally rotated (for VMO) and internally rotated (for VLO), respectively, while extending their knees against resistance to maximize activation. For the BF, participants were seated with their knees bent at 60° and performed knee flexion against resistance to target BF activation [5].

During the squat exercise participants flexed their knees at 95° at a randomly selected ankle angle. Each squat was performed thrice, with the knee reaching the set angle and holding the position for 5 seconds, followed by a 5-second rest period between repetitions. The ankle positions were adjusted using wedge boards set at –20°, 0°, and 20° (Figure 2).

Figure 2. Different ankle angle with squat position (A) plantarflexion (–20°), (b) neutral position (0°), and (C) dorsiflexion (20°).

The knee joint angle of 95° was chosen based on evidence that knee extension torque increases with greater flexion angles, peaking between 80° and 100° [6]. While 90° is often considered an ideal benchmark for squatting, 95° was selected to better reflect the natural range of motion observed during squatting tasks, providing a more ecologically valid representation of functional movement patterns [7]. This adjustment ensures a balance between maximizing torque generation and maintaining joint stability, while also accommodating slight variability in participants’ squatting mechanics for greater consistency and replicability during repeated trials.

The ankle angles of 20° DF and 20° PF were selected to align with the talocrural joint’s normal range of motion, where 20° represents the upper limit of DF [1]. To ensure consistency and comparability between extreme positions, PF was also set to 20°, enabling a balanced evaluation of lower-limb kinematics and muscle activation patterns during squatting tasks. This symmetrical approach ensures that both ends of the range are equally represented for biomechanical analysis.

6. Equipment

The sEMG analysis was conducted using the Noraxon Ultium Portable Lab system with the MyoMUSCLE software (Noraxon Inc.). This high-performance tool provides precise assessments of muscle activation patterns.

7. Data Analysis

Data were analyzed using repeated-measures analysis of variance (ANOVA) to evaluate differences in muscle activation across ankle positions. Post-hoc analyses with Bonferroni corrections were applied to control the overall alpha level at 0.05 for multiple comparisons. To control for Type 1 error, the significance level was adjusted using Bonferroni corrections, resulting in a corrected threshold of p < 0.017 for pairwise comparisons across three conditions. All statistical analyses were conducted using IBM SPSS version 27.0 (IBM Co.), with the mean value of three trials used for the final analysis.

1. Gluteus Maximus

1) Right side

The analysis indicated a significant effect of ankle angle on right Gmax activation during squatting (Wilks’ Lambda: 0.737; F_2,28 = 5.002; p = 0.014). Muscle activation was significantly higher in DF than in PF (p = 0.010). Additionally, DF resulted in significantly higher activation compared to the NEU position (p = 0.020). No significant differences were observed between PF and NEU positions (p > 0.05).

2) Left side

A significant effect of ankle angle was observed on left Gmax activation (Wilks’ Lambda: 0.781; F_2,28 = 3.919; p = 0.032). DF resulted in significantly higher muscle activation than PF (p = 0.025). No significant differences were observed between the PF and NEU positions.

2. Vastus Medialis Oblique

1) Right side

The right VMO showed a significant difference in muscle activation across the ankle positions (Wilks’ Lambda: 0.530; F_2,28 = 12.394; p < 0.001). Activation was significantly higher during PF than during DF (p < 0.001), whereas no significant difference was observed between the PF and NEU positions.

2) Left side

The left VMO also displayed a significant effect on the ankle angle (Wilks’ Lambda: 0.657; F_2,28 = 7.320; p = 0.003). PF showed significantly higher activation than that of DF (p = 0.002), with no significant difference between the PF and NEU positions.

3. Vastus Lateralis Oblique

1) Right side

No significant overall effect of ankle angle was observed on right VLO activation (Wilks’ Lambda: 0.828; F_2,28 = 2.911; p = 0.071), although the trends suggested an increased activation during DF.

2) Left side

The ankle angle had a significant effect on the activation of the left VLO (Wilks’ Lambda: 0.650; F_2,28 = 7.548; p = 0.002). Activation was significantly higher during PF than during DF (p = 0.003), with no significant difference between the PF and NEU positions.

4. Biceps Femoris

1) Right side

There was no significant effect of ankle angle on the activation of the right BF (Wilks’ Lambda: 0.858; F_2,28 = 2.313; p = 0.118), indicating no meaningful differences between the PF, NEU, or DF positions in terms of muscle activation.

2) Left side

Similarly, no significant effect of ankle angle was observed on the activation of the left BF (Wilks’ Lambda: 0.955; F_2,28 = 0.658; p = 0.526). Muscle activation did not differ significantly across the three ankle positions.

The %MVIC values for the Gmax during squatting were relatively low, ranging from 4.32 to 11.49. This aligns with previous findings that bilateral exercises like squats, particularly those performed without additional resistance, tend to produce lower muscle activation compared to unilateral or dynamic exercises. Furthermore, the isometric nature of the squatting task in this study may have contributed to the reduced Gmax activation, as isometric contractions distribute load across multiple stabilizing muscles [8]. Muscle activation levels are summarized in Table 2. Figure 3 complements this by visually representing the activation patterns and highlighting significant differences between conditions. And the activation ratios of the Gmax relative to other muscles (BF, VMO, VLO) across the three ankle positions are summarized in Table 3. These ratios provide a comparative perspective on the relative contributions of different muscle groups under varying conditions.

Table 2 . Mean difference about %MVIC across the three different ankle positions during squats.

Target muscle (µV)	Ankle position (%MVIC)
	Plantarflexion (–20°)	Neutral position (0°)	Dorsiflexion (20°)
Gmax Rt*	4.50 ± 0.66a	4.32 ± 0.61ab	5.46 ± 0.86b
Gmax Lt*	6.16 ± 0.86a	8.19 ± 1.82ab	11.49 ± 2.32b
VMO Rt*	58.50 ± 4.39b	58.26 ± 4.16b	45.06 ± 3.53a
VMO Lt*	47.64 ± 4.22b	47.02 ± 4.27b	35.29 ± 4.10a
VLO Rt	42.53 ± 5.00a	40.43 ± 4.42a	35.56 ± 4.61a
VLO Lt*	38.52 ± 4.34b	37.57 ± 4.14b	28.34 ± 4.12a
BF Rt	9.30 ± 1.97a	9.72 ± 1.69a	11.62 ± 1.72a
BF Lt	10.16 ± 1.70a	10.04 ± 1.74a	10.93 ± 1.78a

Values are presented as mean ± standard deviation. %MVIC, percentages of maximum voluntary isometric contraction; Gmax, gluteus maximus; VMO, vastus medialis oblique; VLO, vastus lateralis oblique; BF, biceps femoris; Rt, right; Lt, left. *p < 0.05. ^a,b,abIndicate statistical significance, with the alphabetical order reflecting the relative magnitude (i.e., a < ab < b), where ab denotes an intermediate group that is statistically like one group but significantly different from another..

Table 3 . Ratios of Gmax activation to other muscles (BF, VMO, VLO) across different ankle positions.

Ratio	Position	Right	Left
Gmax/BF	PF	0.484	0.600
	NEU	0.444	0.816
	DF	0.470	1.051
Gmax/VMO	PF	0.077	0.129
	NEU	0.074	0.174
	DF	0.121	0.325
Gmax/VLO	PF	0.106	0.160
	NEU	0.107	0.218
	DF	0.154	0.405

The ratios highlight the relative activation of Gmax compared to BF, VMO, and VLO for each side separately, enabling direct comparison of right and left muscle engagement. Gmax, gluteus maximus; BF, biceps femoris; VMO, vastus medialis oblique; VLO, vastus lateralis oblique; PF, plantarflexion; NEU, neutral; DF, dorsiflexion..

Figure 3. Muscle activation levels across ankle position. Muscle activation levels (%MVIC) of the Gmax, VMO, VLO, and BF during isometric squats under three ankle positions: plantarflexion (–20°), neutral position (0°), and dorsiflexion (20°). *Significant differences between conditions are marked with p < 0.05. Error bars indicate standard deviations. %MVIC, percentages of maximum voluntary isometric contraction; Gmax, gluteus maximus; VMO, vastus medialis oblique; VLO, vastus lateralis oblique; BF, biceps femoris.

This study analyzed the effects of ankle positions on Gmax, VMO, VLO, and BF activation during squat exercises. Our results revealed that different ankle positions alter muscle activation patterns, suggesting that adjusting the ankle position can play a significant role in enhancing the effectiveness of rehabilitation and exercise prescriptions. The distinct activation of the Gmax and quadriceps muscles in response to DF and PF of the ankle, presents a promising approach for tailoring exercises to target specific muscle groups.

1. Increased Activation of the Gluteus Maximus in Dorsiflexion

This study analyzed the effects of ankle positions on Gmax, VMO, VLO, and BF activation during squat exercises. Our results revealed that different ankle positions alter muscle activation patterns, which, despite relatively low %MVIC values for the Gmax, may hold clinical significance.

The %MVIC values for the Gmax observed in this study were relatively low compared to values typically reported for closed-chain exercises. This discrepancy can be attributed to the specific characteristics of bodyweight bilateral squats performed in this study. Unlike dynamic or loaded squats, bodyweight squats without additional resistance reduce the overall demand on the hip extensors, as the load is distributed across multiple lower-limb muscles. The bilateral nature of the exercise inherently shares the workload between limbs, further lowering the activation of individual muscles. The isometric contraction required to maintain squatting posture also emphasizes stability over maximal activation, leading to reduced %MVIC values. Despite this, the variations in activation across ankle positions provide valuable insights for clinical applications, particularly in populations with reduced physical capacity.

The activation ratios provide additional insights into the muscle coordination patterns across ankle positions. In particular, the dorsiflexed ankle position demonstrated higher Gmax-to-BF and Gmax-to-quadriceps ratios compared to the plantarflexed position (Table 3). These findings indicate that DF places greater emphasis on the hip extensors, such as the Gmax, while reducing the relative contributions of the hamstrings and quadriceps. Conversely, PF shifts the mechanical load toward the quadriceps, particularly the VMO and VLO, emphasizing their stabilizing roles during knee extension. This differential muscle engagement highlights the adaptability of muscle coordination patterns in response to changes in ankle position, allowing for targeted rehabilitation or training strategies.

The significantly increased activation of the Gmax in the dorsiflexed ankle position is likely due to the increased demand for hip extension and the forward tilting of the trunk, which shifts the load to the hip joint and enhances Gmax engagement [9]. In isometric conditions, this shift in body mechanics necessitates greater Gmax activation to maintain joint stability and balance, reducing the reliance on compensatory muscles such as the hamstrings or lumbar extensors.

While the DF position offers potential for increasing Gmax activation, achieving substantial gains in hip extensor strength typically requires the addition of external resistance, such as barbells or dumbbells, to increase the mechanical load. Furthermore, unilateral variations of the squat, such as split squats or single-leg squats, can further enhance Gmax engagement by introducing greater stability demands and reducing the distribution of load across both limbs. These adaptations, when combined with the biomechanical advantages of the DF position, may support advanced training programs aimed at maximizing Gmax activation and improving performance in activities requiring powerful hip extension, such as sprinting, jumping, or weightlifting [10].

These findings underscore the potential for tailoring squat exercises based on ankle positioning to achieve specific rehabilitation goals. For instance, the DF position may be particularly beneficial for individuals requiring improved hip extensor strength, while the PF position may better support quadriceps-focused training for knee stability. By integrating such adjustments into exercise prescriptions, clinicians and trainers can optimize muscle engagement and functional outcomes.

2. Increased Quadriceps Activation in Plantarflexion

In contrast, PF during squats led to greater activation of the VMO and VLO, indicating its ability to strengthen knee-stabilizing muscles. This positioning shifts the body’s center of mass forward, placing a greater load on the knee and encouraging quadriceps engagement [11].

A notable asymmetry was observed between the right and left VLO activation patterns. While no significant effect of ankle angle was detected on the right VLO, a significant increase in activation during PF was noted for the left VLO. This asymmetry may be attributed to individual differences in muscle dominance or neuromuscular control, as dominant limbs often exhibit higher efficiency in motor unit recruitment and activation patterns. Additionally, slight variations in electrode placement or postural alignment during squatting may have contributed to the observed differences.

This increased demand on the quadriceps, particularly on both the VMO and VLO, highlights the role of PF in enhancing knee stabilization. VMO strengthening is critical for maintaining patellar alignment and preventing knee valgus [12], while VLO activation supports lateral knee stability. This PF effect aligns with the finding that forward weight-shifting enhances knee extensor activity, providing a distinct advantage in targeted knee stabilization [11]. Therefore, incorporating PF into knee-focused rehabilitation programs may be effective for enhancing quadriceps strength without overstressing the hip joints. Additionally, this approach could serve as a preventive measure for athletes at risk of knee injuries as it reinforces quadriceps control in movement patterns common in sports such as running [13].

3. Limited Activation of the Biceps Femoris Across Ankle Positions

This study observed no significant differences in BF activation across the three ankle positions, suggesting that ankle positioning has minimal impact on the biomechanical demands of this muscle during squats. As a biarticular muscle, the BF plays a dual role in hip extension and knee flexion. However, the isometric nature of the squatting task in this study limited the dynamic joint movements typically associated with BF recruitment [14]. Consequently, the BF was not substantially engaged, regardless of ankle position.

The distributed load inherent to bilateral squats further contributed to the consistent activation levels observed in the BF. In bilateral movements, the workload is shared between the limbs, reducing the activation demands on individual muscles like the BF. Additionally, the changes in ankle positioning primarily affected muscles that directly contribute to sagittal plane stability, such as the quadriceps and Gmax, rather than muscles like the BF, which are more sensitive to variations in hip or knee joint angles [15].

While the BF did not show significant activation differences across ankle positions, this consistency suggests that its role during squats is primarily supportive, aiding in the stabilization of the lower limb rather than acting as a primary mover. Future studies may explore whether dynamic or unilateral variations of squats, combined with specific ankle positioning, can elicit greater BF activation and optimize its engagement in functional movement patterns.

4. Limitations and Future Directions

Although this study offers important insights into the effect of ankle positioning on muscle activation during squats, several limitations should be acknowledged. First, this study did not account for variables such as foot width and the squat depth, which significantly influence muscle activation patterns. Wider foot positioning tends to increase Gmax activation and trunk stability, whereas deeper squats place a greater load on the knee and hip joints, enhancing muscle engagement in these areas [16,17].

Additionally, this study primarily focused on key muscles, including the Gmax, VMO, VLO, and BF, without considering the semitendinosus, semimembranosus, and other hamstring muscles that contribute to hip extension and stability. Including these muscles in future studies could provide a more comprehensive understanding of muscle interactions and their cooperative functions during squats [18].

Finally, this study only examined the short-term effects of adjusting ankle positions. Future studies should investigate the long-term effects of such adjustments on muscle strength and activation, particularly in populations with specific rehabilitation needs, such as older individuals or those with a history of hip or knee injuries. Expanding research on these populations would enhance the generalizability of our findings and provide valuable data for designing customized rehabilitation programs.

Our study underscores the importance of ankle positioning in squat exercises, showing that DF enhances Gmax activation for hip stability, while PF promotes quadriceps activation, especially in VMO and VLO, which are crucial for knee stabilization. These findings suggest that integrating DF and PF positions into targeted rehabilitation programs could optimize muscle engagement, support joint stability, and reduce compensatory muscle strain. Future research should focus on long-term effects and diverse populations to validate these ankle-positioning strategies for improving lower-limb stability and function.

None.

None to declare.

No potential conflicts of interest relevant to this article are reported.

Conceptualization: HL, IM, CY. Data curation: HL, CY. Formal analysis: HL, CY. Investigation: HL. Methodology: HL, IM, CY. Project administration: HL, IM, CY. Resources: HL. Software: HL. Supervision: HL, IM, CY. Validation: HL, IM, CY. Visualization: HL. Writing - original draft: HL, CY. Writing – review & editing: HL, CY.