Differences in triceps surae muscle dynamometry and electromyography between adult males and females

Abstract

The triceps surae performs vital functions during locomotion and possesses shock-absorbing capacity. The injury rate of the Achilles tendon is higher in males than females. Quantification of the triceps surae muscle force outputs across sexes has not been determined. This study aimed to investigate and quantify sex-related triceps surae isokinetic parameters and activation magnitudes. A repeated-measures comparative design is implemented. A total of 20 males and 20 females joined this study. An isokinetic dynamometer and a synchronized electromyography system were employed to measure isokinetic torque, power, work, and muscle amplitude during the dynamic plantar flexion test. The participants performed 3 trials at 2 knee angles to target the gastrocnemius and soleus. There were sex-related differences in triceps surae performance. Males demonstrated more isokinetic torque, power, and work (P < .05) than females. Males scored more normalized peak torque (49% and 80%) and work (47% and 108%) than females in extended and right-angled knees, respectively. All participants demonstrated improved isokinetic output when the knee was extended rather than flexed. The triceps surae muscle compartments were activated uniformly across sexes (P > .05). Males exerted greater plantar flexion isokinetic parameters than their female counterparts. Males may be more likely to sustain injuries than females due to increased strain on the Achilles tendon caused by greater torque and power output. Such differences may impact athletic performance, injury risk, functional tasks, and job demands. Therefore, clinicians and ergonomists could consider this finding when developing successful rehabilitation programs and maintaining workplace safety.

1. Introduction

The triceps surae is the leading engine for the progression of movement in the human body.^[1] The back of the lower legs houses the powerful group of muscles responsible for executing essential movements such as walking,^[2] running,^[3] and other dynamic activities.^[4] The triceps surae muscle helps stabilize the ankle joint,^[5] maintains locomotion, and positions the body upright. As soon as the foot strikes, the calf muscle absorbs and dissipates shock, spreads the pressure into the joints of the lower limbs, restrains forward progression of the tibia, and contributes to knee stability.^[1] The Achilles tendon is pivotal in delivering power to the foot from the triceps surae muscles while engaging in various activities, including walking, running, and jumping.^[1,6,7] The Achilles tendon is subjected to high loads during daily activities.^[7] Although a firmer tendon can enhance its ability to absorb and dissipate forces, it may also become less flexible. As a result, this reduced adaptability could increase the risk of developing conditions such as tendonitis or Achilles tendon rupture.^[8]

Achilles tendon injuries are sex-specific. The ratio of males to females with Achilles tendon rupture was reported to be 5:1.^[9] According to previous studies, males have stiffer tendons than do females,^[10,11] possibly explaining why males sustain injuries at a higher rate than do females. These sex-related differences in the mechanical properties of tendons may be attributed to the high estrogen levels in females.^[9] Therefore, females demonstrate higher elasticity of tendons than that observed in males. Conversely, males have a greater body mass and force generation capacity than their female counterparts. Increased body mass necessitates weight-bearing tendons to withstand greater loads, which increases the size and stiffness of the tendon. Tendon stiffness is believed to limit its adaptability to deformation when exposed to a sudden load.^[12]

These variations in tendon mechanical properties between the sexes affect function, motor control, and the risk of injury.^[11] As mechanical properties of the skeletal muscles influence their performance, studying the dynamic activity of the triceps surae muscle across genders could provide valuable insights into how structural differences affect muscle productivity. Single-muscle productivity was evaluated using an isokinetic dynamometer.^[13] Muscle torque, work, and power are crucial factors contributing to overall function. During isokinetic contractions, the dynamometer maintains a constant velocity over a predetermined range of motion; however, the force produced remains unrestricted and depends on the participant’s effort and ability.^[14,15]

Previous studies that assessed plantar flexion strength in males and females are scarce and considered only the isometric contraction of the triceps surae muscle.^[16] However, 1 study measured only peak isokinetic torque.^[17] To the author’s knowledge, previous studies investigating sex-related differences in the plantar flexor muscle’s performance have utilized various methodologies and a wide age range.^[16] Therefore, the findings were either equivocal or incomplete. Quantifying plantar flexion torque parameters and electromyographic activation of the triceps surae muscle compartment across the sexes may have implications for rehabilitation and sports scientists. This may shed light on the interplay between muscle performance, structural differences, and injury patterns between sexes. The current study aimed to investigate and quantify the isokinetic torque, power, work, and electromyographic muscle activation percentage of the triceps surae muscle components between sexes.

2. Methods

2.1. Study design

This study utilized a repeated-measures comparative design. The study was conducted at the department’s biomechanics lab. The independent variables were sex and knee joint position, which included 2 levels: extension and flexion to 90° to target the triceps surae muscle components: the gastrocnemius muscle medial and lateral heads (GM and GL) and soleus (SOL). The outcome measures were triceps surae muscle peak torque (Pk-T), average torque (Avg. Pk-T), peak torque-to-body weight ratio (Pk-T/BW), average peak torque-to-body weight ratio (Avg. Pk-T/BW), power, work, average work-to-body weight ratio., and electromyography (EMG) activity of the SOL, GM, and GL muscles normalized to maximum voluntary isometric contraction (MVIC). Data were collected from the dominant lower limbs. Three trials were performed for each knee position, and the results were averaged. The order of the knee angle was randomized to avoid the learning effect. Therefore, data collection began with the predetermined participants’ knee angle. The participant’s knee angle was then changed to the next one, and the isokinetic plantarflexion testing trials were repeated. Each participant signed a consent form before commencing the procedures. Each subject visited the lab once to collect the data trials. The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Imam Abdulrahman Bin Faisal University – approval number (IRB‐2017‐03‐064).

2.2. Participants

Forty healthy adults, 20 males (mean age 21.15 ± 1.03 years; height 170.80 ± 4.61 cm, and BMI 22.02 ± 2.76) and 20 females (mean age 21.90 ± 1.29 years; height 156.87 ± 5.74, and BMI 22.72 ± 1.65) with matched age and body mass index (BMI), participated in the present study. None of the participants suffered any musculoskeletal or neurological disorders of the trunk and/or lower extremities, or had participated in athletic activities regularly for at least a year before joining the study.

2.3. Sample size

A priori sample size was computed using G*Power (version 3.1.9.2), F-test, ANOVA, repeated measures within–between interaction. A medium effect size of 0.25 was decided, with 2 groups and 2 measurements.^[18] Considering 85% power, an alpha level of 0.05, 2 study groups, and 2 measurements, the estimated total sample size was 40.

2.4. Instruments

The isokinetic torque, work, and power parameters of the triceps surae muscles were evaluated using a Biodex System 4 Pro-multi-joint dynamometer (Biodex Medical Systems Inc., Shirley). This system has demonstrated high validity and reliability for measuring muscle performance.^[19] The isokinetic dynamometer was calibrated before data collection for each session. All the test trials were performed with the participants seated in a Biodex chair with the back support inclined at 70°. The knee joint was positioned at either 0°or 90 ° angle. The isokinetic velocity was set at 60°/s. The ankle movement range was set between 10° dorsiflexion and 30° plantar flexion.

Surface EMG data were collected unilaterally from the GM, GL, and SOL muscles using the Delsys Trigno wireless EMG system (Delsys Inc., Natick). The EMG system was synchronized with the isokinetic dynamometer. The recording unit comprised 2 parallel silver bar electrodes with a 1-cm inter-electrode distance. Surface EMG data were collected at a sampling rate of 2000 Hz using EMGworks® software (Delsys Inc., Natick).

2.5. Procedures

The participants’ demographic data were measured and recorded on a personal information sheet. The experimental procedures were then initiated with skin preparation for the placement of EMG electrodes according to the SENIAM^[20] and ISEK^[21] recommendations. The participants’ skin was lightly abraded and cleaned with alcohol wipes to minimize skin resistance and electrode-to-skin artifacts. The targeted muscles were first identified by palpation during contraction, and EMG electrodes were placed over the muscle bellies parallel to the orientation of the muscle fibers. Surface EMG electrodes were placed over the SOL, on the lower medial third of the posterior leg, approximately two-thirds of the distance between the medial femoral condyle and the medial malleolus; the GM, just distal to the knee on the upper third of the posterior leg and over the maximal medial girth; and the GL, 1 cm above the GM on the lateral side, that is, 1 cm proximal to the maximum girth.^[22,23] Before data collection, a signal quality check was performed to detect baseline noise or artifacts.

The triceps surae muscle compartments’ MVIC measurements were recorded while the participants were seated on the isokinetic chair. The trunk and pelvis were supported using velcro straps for stabilization. Based on a predetermined randomization, the knee joint was set at a predetermined angle (90 or 0) using thigh and leg support pads, as necessary. Lastly, the foot was affixed to the footplate using customizable straps. The axis of ankle joint movement was aligned with that of the dynamometer. Before commencing data collection, the participant performed 3 familiarization trials.

Following electrode placement and seating on the isokinetic chair, participants were asked to perform MVIC of the triceps surae in each knee position, with the ankle maintained in a neutral position. To accomplish the MVIC, each participant was asked to perform 3 repetitions of a maximum effort contraction of the triceps surae muscle by pushing the foot against the fixed footplate of the isokinetic chair. Each participant was instructed to start slowly increasing the force, reaching maximum effort after 3 seconds, hold it for 3 seconds, and calm down with 3 seconds. The highest amplitude recorded for each muscle compartment is used as a reference for normalization to calculate the % MVIC during the dynamic trials. A 5-minute rest was followed to avoid muscle fatigue. The participants then performed isokinetic plantarflexion dynamic trials. During dynamic trials, participants were instructed to move their ankle through the preset range of motion (from 10° dorsiflexion to 30° plantar flexion) with maximum effort. Three repetitions were performed for each test condition (knee joint angle), and a 2-minute rest interval was allowed between trials. The isokinetic data and the synchronized EMG muscle activity of the triceps surae muscle were recorded for test trials. After completing the data collection process, the participants were removed from the isokinetic device. The surface EMG electrodes were removed, and the skin underneath was cleaned and inspected for irritation. Procedures are depicted in Figure 1.

Figure 1.

Flow chart of the study procedure.

2.6. Data processing

The isokinetic data were obtained for each participant using the isokinetic software (Biodex Advantage 4.63, Biodex Medical Systems Inc., Shirley). A comprehensive report of the outcome parameters was generated, and the data were then uploaded to an Excel spreadsheet for analysis.

EMG processing was conducted using EMGWorks analysis software. Normalizing muscle activation amplitude parameters to a reference value, such as the MVIC of a reference contraction, allows for comparison between groups. This postprocessing method employs the maximum root mean square value from the recorded MVIC trials to normalize the EMG data series. The raw EMG data series were linearly enveloped through rectification and band-pass filtering by a width of 10 to 500 Hz, and the data were visually inspected. The data had a common mode rejection ratio exceeding 80 dB, a baseline noise below 0.75 uV RMS, and a gain of 1000. MVIC’s highest linear enveloped EMG magnitude of each electrode site for each participant is determined. Subsequently, all dynamic plantarflexion isokinetic trials from the 3 electrodes of the triceps surae muscle were normalized as a percentage of MVIC to enable comparison of EMG magnitude across participants.

2.7. Statistical analysis

Data were analyzed using IBM SPSS version 29 (SPSS, Chicago). The significance level (α) was set at P ≤ .05 for all statistical analyses. Descriptive statistics and independent t-tests were performed to compare demographic data between the groups. The Schapiro–Wilk test was used to check the homogeneity of data, revealing the normal distribution of data. Mixed-effects ANOVA was employed to examine the sex effect, knee angle (0° and 90°) effect, and their interaction in all isokinetic parameters and normalized EMG for the triceps surae components. Levene test ensured homogeneity of variance. A pairwise comparison was conducted in case a significant interaction was noted for any outcome measures. Bonferroni corrections were applied to counteract multiple comparisons and minimize the possibility of type I errors.

3. Results

The demographic data were compared between groups, and there was a significant difference in weight and height (P = .000 and P = .003, respectively). Moreover, male participants had higher values than female participants. However, no significant difference was observed in age or BMI between the groups (P = .051 and P = .341) (Table 1).

Table 1.

Participants’ characteristics, Mean ± SD.

Group	Age (yr)	Height (cm)	Weight (kg)	BMI
Males, n = 20	21.15 ± 1.03	170.80 ± 4.61	64.32 ± 9.19	22.02 ± 2.76
Females, n = 20	21.90 ± 1.29	156.87 ± 5.74	56.13 ± 6.86	22.72 ± 1.65
P-value	.051	.000	.003	.341

BMI = body mass index, SD = standard deviation.

3.1. Isokinetic parameters

A 2 × 2 mixed ANOVA was conducted to determine the main effects of sex and knee position and their interaction on isokinetic parameters of the triceps surae muscle isokinetic testing. Overall, the results revealed that males performed better than females in all isokinetic parameters (P ≤ .05; Table 2). In addition, participants performed better in the extended knee than in the flexed position. There was an interaction between sex and knee position in terms of the Avg. Pk-T/BW (P = .042, η_p² = 0.104), Avg. power (P = .027, η_p² = 0.122), work (P = .011, η_p² = 0.158), and work/BW (P = .005, η_p² = 0.186) (Table 2). However, no interaction effect was found to be significant for Pk-T (P = .177, η_p² = 0.047), Avg. Pk-T (P = .076, η_p² = 0.081), and Pk-T/BW (P = .005, η_p² = 0.119). The mean scores for the female group decreased over the flexed knee position compared to the extended position for all the isokinetic outcome measures. The mean scores for the males changed significantly across positions. In the flexed knee position, males scored lower parameters than the extended position for Pk-T (P = .032), Avg. Pk-T (P = .056), Pk-T/BW (P = .046), and Avg. Pk-T/BW (P = .081). However, the Avg. power, work/BW, and work were not dependent on knee positions (P > .05).

Table 2.

Mean (SD) and 95% CI of the isokinetic data and normalized EMG as a function of gender in the 2 knee angles.

Outcome measures	Group	0° knee position mean ± SD (95% CI)	90° knee position Mean ± SD (95% CI)	Sex effect	Position effect	Interaction effect
Pk-T (N.m)	M	86.62 ± 24.22* (76.12–96.86)	80.06 ± 21.38* (70.94–89.76)	P = .001	P = .000	P = .177
	F	50.97 ± 18.92** 75.87–97.03	38.68 ± 8.64** (34.83–42.20)
Avg. Pk-T (N.m)	M	81.09 ± 23.47 (70.99–90.98)	75.66 ± 20.61 (66.79–84.53)	P = .000	P = .000	P = .076
	F	46.75 ± 19.24** (38.82–54.48)	34.21 ± 8.72** (30.33–37.82)
Pk-T/BW (%)	M	134.29 ± 31.74* (120.21–147.47)	124.21 ± 27.11* (111.86–135.69)	P = .000	P = .000	P = .119
	F	90.32 ± 30.99** (77.74–103.20)	69.13 ± 13.84** (63.05–74.39)
Avg. Pk-T/BW (%)	M	125.63 ± 31.00 (112.28–138.56)	117.35 ± 26.71 (105.38–128.42)	P = .000	P = .000	P = .042
	F	83.02 ± 31.94** (70.29–96.08)	60.89 ± 13.03** (55.17–65.78)
Avg. power (watt)	M	35.66 ± 14.31 (29.75–41.95)	34.70 ± 15.42 (28.42–41.55)	P = .000	P = .005	P = .027
	F	18.64 ± 11.92** 13.91–23.67	11.21 ± 3.16** (9.77–12.44)
Work (Joule)	M	129.74 ± 38.09 (113.28–146.05)	123.39 ± 38.42 (106.48–140.02)	P = .000	P = .000	P = .011
	F	77.45 ± 39.05** (61.78–93.83)	52.03 ± 16.11** (44.91–58.79)
Work/BW	M	201.35 ± 51.47 178.27–223.46	191.17  ± 51.36 (169.47–213.27)	P = .000	P = .000	P = .005
	F	136.92 ± 64.27** (111.53–162.56)	92.00  ± 24.22** (81.29 ± 101.49)
SOL (%MVIC)	M	90.77 ± 7.96 (86.99–93.47)	87.77 ± 10.80 (82.36–91.85)	P = .473	P = .001	P = .146
	F	91.29 ± 3.70** 89.62–92.79	83.97 ± 10.16** 79.43–88.47
GM (%MVIC)	M	88.71 ± 11.75 (83.11–93.11)	87.81 ± 10.25 (83.00–91.74)	P = .088	P = .402	P = .218
	F	91.67 ± 5.47 89.11–93.56	90.85 ± 5.22 88.43–92.92
GL (%MVIC)	M	91.27 ± 5.66 (88.36–93.68)	86.70 ± 16.83 (77.78–91.64)	P = .419	P = .282	P = .300
	F	91.06 ± 8.25 87.10–94.11	90.98 ± 7.73 87.46–93.82

Bold numbers indicate the mean difference is significant at the 0.05 level.

Avg. = average, BW = body weight, CI = confidence interval, EMG = electromyography, F = female, GL = lateral gastrocnemius, GM = medial gastrocnemius, M = male, N.m = Newton meter, Pk-T = peak torque, SD = standard deviation, SOL = soleus.

^*Significant difference between knee angles within the male group.

^**A significant difference between knee angles within the female group.

The means of the 2 groups’ isokinetic parameters are further compared by quantifying the percentage difference of each outcome measure in each knee position as displayed in Table 3. Based on this further analysis, the Avg. power appeared to be the biggest sex‐related gap, followed by Work at right-angled knee position – males are 210%, and 137% higher than females, respectively. Those outcomes are therefore the most divergent between the groups. Regarding the normalized parameters to body weight, males scored more normalized Pk-T/BW (49% and 80%) and work/BW (47% and 108%) than females in extended and right-angled knees, respectively.

Table 3.

Percentage difference in isokinetic parameters means between males and females in the 2 knee angles.

Outcome measures	Percentage difference (male vs female) 0° knee position	Percentage difference (male vs female) 90° knee position
Pk-T (N.m)	+70%	+107%
Avg. Pk-T (N.m)	+73%	+121%
Pk-T/BW (%)	+49%	+80%
Avg. Pk-T/BW (%)	+51%	+93%
Avg. power (watt)	+91%	+210%
Work (Joule)	+68%	+137%
Work/BW	+47%	+108%

Percentage difference is expressed relative to the female mean: positive = male > female.

Avg = average, BW = body weight, N.m = Newton meter, Pk-T = peak torque

3.2. EMG activity

Comparisons of the triceps sura muscle compartments during the isokinetic trials did not result in an interaction effect of group and position in the normalized EMG data (%MVIC) of (SOL, GM, and GL); (P = .146, η_p² = 0.055), (P = .218, η_p² = 0.040), (P = .300, η_p² = 0.028) respectively. In addition, the normalized EMG data didn’t change across groups (SOL: P = .473, η_p² = 0.014, GM: P = .088, η_p² = 0.075, and GL: P = .419, η_p² = 0.017). However, a significant difference was observed in the EMG activation percentage of the soleus muscle compartment between the knee positions (flexed and extended knee positions) during isokinetic plantar flexion (P = .001). Mean scores for the SOL muscle increased in the extended knee position compared to the flexed one only in the female group (Table 2).

4. Discussion

The muscles surrounding the ankle play crucial roles in generating torque and power, which help maintain body stability, prevent it from toppling, and facilitate movement through the environment. This study examined the triceps surae muscle isokinetic parameters and EMG activity during isokinetic contraction performance to assess whether sex-related differences exist in torque, power, work, and %MVIC parameters. The study participants performed isokinetic ankle plantar flexion contraction in 2 knee positions (extended and right-angle flexed) to determine if plantar flexors’ performance is impacted by sex or knee position. The findings demonstrated that sex and knee angle could affect the isokinetic torque, power, and work parameters.

The results revealed a significant difference between the sexes in the isokinetic Pk-T, Avg. Pk-T, Pk-T/BW, Avg. Pk-T/BW, power, work, and work/BW. Among the dynamometer outcome measures studied, 3 parameters are normalized to body weight, namely, Pk-T/BW, Avg. Pk-T/BW, and work/BW. Normalized parameters help compare the outcome measures across males and females by accounting for differences in body weight across sexes, allowing equitable comparison. Notably, males scored higher than females for all isokinetic parameters, including the normalized ones. During the isokinetic test trials (extended and flexed knee positions), all participants exerted more plantar flexion torque in the extended knee position than in the flexed knee position. Furthermore, female participants exhibited more plantar flexion torque, power, and work values for the extended knees. Additionally, males scored higher torque values in extended knee than in flexed knee. In contrast, no sex-related differences were noticed in the normalized EMG muscle compartment activation (%MVIC) across the groups.

The results of the current study demonstrated that males exerted more isokinetic torque, work, and power than females. These results agree with those of previous studies that showed higher plantar flexor force^[16] and static torque^[17] in males than in females. This difference is attributed to the notion that males generally possess more muscle mass than the mass observed in females, which directly contributes to increased force production.^[24] Among the factors that might be responsible for the noted differences in torque productivity between genders are the structural differences in skeletal muscle fiber composition between males and females. Males have a higher proportion of type II muscle fibers compared to type I fibers. Conversely, type I skeletal muscle fibers are more prevalent in women than men.^[25] Type II fibers are known to possess 10% to 20% more contractile force than that exerted by type I fibers. Additionally, they are believed to be ideal for activities requiring high-force movement and weightlifting.^[26] Further, the cross-sectional area of type II fibers is larger in males than in females.^[27] Notably, the triceps surae muscle is composed of a mixture of type I and II muscle fibers. One component of the triceps surae, the 2 heads of gastrocnemius, comprise 50% to 60% of type-II muscle fibers.^[28] However, the SOL muscle, the other component of the triceps surae comprises mainly type I muscle fibers. Another factor that could play a significant role in justifying the higher torque productivity in males than in their female counterparts is the geometrical difference in muscle architecture. Moreover, males possess larger muscular physiological cross-sectional areas than females. This is particularly true for the patella and Achilles tendons.^[8] These potential discrepancies in size and fiber type may contribute to the gender-related differences in muscle force production and, therefore, the isokinetic torque measures discrepancies observed in the current study. Interestingly, the observed discrepancies in the current work revealed that normalized peak torque values of the males exceeded females by 49% and 80% for gastrocnemius and soleus compartments, respectively.

The present study demonstrated that males exerted more power and work than females during isokinetic plantar flexion. When normalized to BW, the work done by the males’ triceps surae muscle exceeded females by 47% when the knee is extended, and the work is doubled for the flexed position (108%). The work measure reflects the capability of the muscle to maintain torque over distance or the amount of force produced over a range of motion. While muscle power is the product of force and velocity, it is dependent on the torque output, and it describes how effectively the muscle can perform work over time.^[29] Isokinetic contractions are dynamic patterns that are distinguished by the dynamometer maintaining a constant velocity over a predetermined range of motion.^[13,30] Therefore, the force produced is unconfined and determined by the participant’s capacity.^[14,15] Thus, the isokinetic system allows for control over the task’s duty cycle because the velocity is fixed. The overall function is believed to be significantly influenced by muscle power.^[31] Consequently, it may be inferred that the muscle’s torque capability was the primary determinant of power output. Torque was markedly improved for males compared to females. Thus, muscular power as well as work is anticipated to have a comparable response. To the authors’ knowledge, no previous research has compared the triceps surae muscle power or work between sexes. Such an increase in work and power levels shown in this study for the male group may elucidate the elevated incidence of Achilles tendon injuries among males.

According to the current study, males and females exerted greater isokinetic torque when the knee was extended than when the knee was flexed. These findings agree with those of the previous studies^{[15,30,32,33]} that reported increased plantar flexion torque with extended knee position. The gastrocnemii tendons traverse both the ankle and knee joints anatomically. Additionally, they are a primary source of plantar flexor torque. All plantar flexors contribute to the total ankle extensor torque when the knee is extended; however, the gastrocnemius is at a neuromechanical disadvantage when the knee is flexed (90° or greater), which lowers the isokinetic plantar flexor torque.^[15,32] Considering that the gastrocnemii is a 2-joint muscle, bending the knee with ankle plantarflexion reduces the muscle’s fascicular length.^[34] As knee flexion mechanically disadvantages the gastrocnemii, the SOL becomes the primary generator of plantar flexor torque.

Regarding EMG activation throughout the triceps surae muscle compartments during dynamic ankle plantar flexion, the results of the current study demonstrated no sex-related differences in the %MVIC of the electrodes (SOL, GM, and GL). Notably, the EMG activation measured in this study was normalized to MVIC. This indicates the magnitude of the muscle activation pattern exerted by the participants as a percentage of their maximum capability. The data also revealed that the gastrocnemius compartment of the triceps surae muscle seemed to be activated uniformly across the sexes throughout different positions. Conversely, the SOL compartment exerted 9% more amplitude when the knee was extended than when it was flexed in the female group. However, the SOL muscle activated equally across the knee positions in males. The observed reduction of the SOL muscle activation in a flexed knee compared to an extended knee in the female group might be explained by the concept that calf muscle strength may vary by altering knee position. Flexing the knee would decrease the muscle’s force productivity in females. Remarkably, the SOL torque capacity, which refers to its force, is restricted in regular users of high-heeled footwear compared to nonusers.^[13] Despite not being considered in the eligibility criteria of the female group, high-heel use, if present in the included participants, might restrict the SOL muscle activation, specifically with flexing the knee.

This study has some limitations that must be acknowledged. Healthy adults were included in this study. Therefore, examining different age groups may influence muscle performance. This study did not consider testing the impact of fatigue on muscle performance between sexes. As noted earlier, physiological discrepancies between males and females may affect muscle performance in the case of fatigue. The present study did not account for the exclusion of high-heeled wearers in the eligibility criteria, which might have influenced the calf muscle strength in the female group and hence, affected the results. Thus, future research assessing muscle force around the ankle should consider this factor.

Unique to this study is the quantification and comparison of triceps surae muscle dynamometric parameters such as torque, work, power, and muscle activation across males and females. This study concluded that adult males exerted more isokinetic torque, power, and work than those demonstrated by females. The high torque and power output might contribute to an increased load on the Achilles tendon and, hence, higher potential injury rates in males compared to those in their female counterparts. The triceps surae muscle compartments exhibited similar activation amplitudes in both sexes during the isokinetic plantar flexion contraction. Men tend to have greater calf muscular strength compared to women, which can influence sports performance, injury susceptibility, functional activities, and occupational requirements. Identifying these distinctions is essential for developing efficient rehabilitation programs, customizing post-surgical rehabilitation programs, understanding functioning task demands, and ensuring workplace safety across sexes. Future studies may consider comparing muscle dynamometric performance across sexes in the athletic populations and elderly people.

Acknowledgments

The author acknowledges Ahmed Farrag, Nora Almulhim, and Moath Almusallim for contributing to the calibration of the isokinetic device, adjustment of isokinetic attachment, and subjects’ consent. The author thanks the volunteers who participated in the study.

Author contributions

Conceptualization: Walaa Hamdy Elsayed.

Data curation: Walaa Hamdy Elsayed.

Formal analysis: Walaa Hamdy Elsayed.

Investigation: Walaa Hamdy Elsayed.

Methodology: Walaa Hamdy Elsayed.

Project administration: Walaa Hamdy Elsayed.

Validation: Walaa Hamdy Elsayed.

Writing – original draft: Walaa Hamdy Elsayed.

Writing – review & editing: Walaa Hamdy Elsayed.