Isokinetic outcome measures and functional performance: Evaluating the utility of the 5-times squat-to-stand test

INTRODUCTION

Physical fitness encompasses multiple components, among which lower-limb absolute strength and muscular endurance are essential for preserving mobility, independence, and overall functional capacity. A comprehensive evaluation of lower-limb function requires the integration of both clinical and functional assessments to accurately capture performance capabilities and underlying neuromuscular integrity in healthy individuals.^[1-6]

Isokinetic dynamometry is considered the gold-standard method for evaluating muscular function, providing precise measurements such as peak torque, average torque (Nm), and average power across various angular velocities. Although isokinetic assessments at angular velocities of 60°/s and 180°/s provide valuable insights into lower-limb strength and power, their relationship with functional performance outcomes remains insufficiently investigated.^[7-9] Moreover, despite its high reliability and diagnostic value, isokinetic testing is often constrained by limited accessibility, high cost, and the need for specialized facilities and personnel.

To address this gap in the literature, the field has increasingly turned to functional performance tests that are simple, quick, and practical to administer.^[10] Among the most widely cited and validated is the 5-Times Sit-to-Stand Test (5×STS), which is extensively used in geriatric populations to assess lower-limb strength, balance, and fall risk. The 5×STS has demonstrated strong psychometric properties and clinical relevance in older adults; however, its applicability to younger, healthy individuals is limited due to the lower physical demands of the task.

Recognizing the need for a more functionally appropriate test for active populations, the 5-Times Squat-to-Stand Test (5×SqTST) was examined in a cohort of healthy college students.^[11] The simplicity of the 5×SqTST, along with its minimal equipment requirements, enhances its practicality. Unlike the traditional sit-to-stand model, this test eliminates chair support. It requires greater neuromuscular control, range of motion, and power generation, making it particularly suitable for assessing lower-limb functional integrity in healthy young adults, such as college students, a population undergoing notable physical and lifestyle transitions that may influence musculoskeletal performance.

Although both isokinetic testing and functional squat-based assessments provide insight into lower-extremity performance, the relationship between isokinetic outcome measures and the 5×SqTST remains underexplored. Establishing such a relationship would support the utility of the squat-based test as a viable clinical proxy for inferring muscle performance, monitoring progress, and guiding rehabilitation in settings where laboratory-based evaluations are not feasible. The research question driving this inquiry is: To what extent is performance on the 5×SqTST associated with isokinetic muscle performance of the knee extensors?

The primary objective of this research was to examine the correlation between isokinetic knee extensor performance (peak torque, Nm, and average power) and the outcomes of the 5×SqTST in healthy female college students. It was hypothesized that no significant association would be found between isokinetic variables and 5×SqTST performance. The secondary objective was to compare isokinetic outcome measures and 5×SqTST performance between recreationally active and inactive college students. It was hypothesized that there would be no significant differences between the two groups.

MATERIALS AND METHODS

5×SqTST

The 5×SqTST^[11] was employed as a practical, functional assessment to evaluate lower-limb performance in healthy college students. This test offers a straightforward and time-efficient method for assessing key components of functional capacity, including transitional movement skills, dynamic balance, postural control, and neuromuscular coordination. Participants were instructed to perform five consecutive squats from a standing position, keeping their hands on their chest, maintaining proper alignment and control throughout the movement [Figure 1]. The total time to complete five repetitions was recorded using a digital stopwatch. Testing occurred in a controlled setting, with standardized verbal instructions and demonstrations provided beforehand. Due to its simplicity, minimal equipment needs, and ease of administration, the 5×SqTST is a practical tool for assessing physical function in young, healthy individuals in both clinical and field environments. Its relevance in assessing functional mobility makes it a suitable proxy for more complex laboratory-based assessments. Participants were provided standardized rest periods of 2–3 min between repeated trials to minimize fatigue effects. The order of assessments was kept consistent for all participants, beginning with the 5×SqTST, followed by isokinetic strength testing. This sequence was chosen to avoid any residual fatigue from isokinetic testing that could negatively influence functional performance.

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Figure 1:

The 5-times-squat-to-stand test illustrates (a) the full squat position and (b) the return to the standing position.

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RESULTS

Table 1 presents the descriptive statistics for both quantitative and qualitative variables, as well as the sociodemographic characteristics of the study participants. The Wilcoxon signed-rank test identified statistically significant differences in isokinetic knee extension performance between the two angular velocities (60°/s and 180°/s) for the dominant limb. The median average power was significantly greater at 180°/s (P < 0.001), reflecting an increase in power output at higher speeds despite a decline in torque. Conversely, the median values for peak torque and Nm were significantly higher at 60°/s than at 180°/s (P < 0.001), consistent with the known inverse relationship between torque production and movement velocity. These findings align with the established physiological force–velocity relationship and emphasize the utility of isokinetic testing in detecting velocity-specific variations in muscular performance [Table 2].

Among the isokinetic outcome measures analyzed, average power was used as a representative example due to its functional significance in capturing dynamic muscular performance. Wilcoxon Signed-Rank analysis indicated a statistically significant distinction between the two conditions (Z = 5.90, P < 0.001). Of the total sample, 47 participants demonstrated higher average power at 180°/s compared to 60°/s, while only 7 participants exhibited the opposite trend. No ties were observed. These findings indicate that average power was significantly greater at the faster angular velocity, reflecting the expected increase in power output with movement speed [Figure 2].

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Figure 2:

Bar chart illustrating the median isokinetic average power (Watts) at 60°/s and 180°/s.

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The Mann–Whitney U test was used to evaluate differences in functional and isokinetic outcome measures between recreationally active and inactive participants. No statistically significant differences were observed across any of the isokinetic outcome variables, indicating that recreational activity status did not significantly influence isokinetic muscle performance. Similarly, recreational status did not differentiate performance on the 5×SqTST under either eyes-open or eyes-closed conditions.

Spearman’s correlation analysis revealed a moderate positive correlation (P = 0.64, P < 0.001) between the 5×SqTST performed with eyes open and eyes closed, indicating consistent performance across both visual conditions. The analysis revealed a moderate negative association between 5×SqTST performance and isokinetic average power, particularly at the higher angular velocity of 180°/s (P = −0.39, P = 0.003). Although a negative trend was observed at 60°/s (P = −0.24, P = 0.08), it did not reach statistical significance. These results indicate that longer completion times on the 5×SqTST are associated with reduced muscle power at higher speeds, suggesting the test may be more responsive to performance variations related to high-velocity power output.

All isokinetic outcome measures exhibited strong positive intercorrelations (P < 0.001), reflecting high internal consistency across the assessed parameters of muscular performance. This coherence reinforces the reliability of the isokinetic data. It supports the potential utility of the 5×SqTST, especially at 180°/s, as a practical, functional proxy for lower-limb power output in settings where laboratory-based testing is not feasible [Table 3].

DISCUSSION

The present study demonstrated a moderate negative association between task performance on the 5×SqTST and isokinetic power output at higher angular velocity (180°/s), suggesting that individuals who complete the task more slowly tend to exhibit lower dynamic muscle power. This finding highlights the clinical relevance of the 5×SqTST as a practical, time-efficient, and equipment-free proxy for assessing neuromuscular function in healthy young females. Given its simplicity and ease of administration, the 5×SqTST holds promise as a viable clinical proxy for isokinetic testing, especially in settings where access to laboratory-based equipment is limited.

The 5×SqTST is a functional assessment recently employed to evaluate lower-extremity performance.^[11] This test closely replicates the biomechanical demands of everyday activities such as transitioning between standing and squatting postures. Its simplicity, combined with the ability to capture essential components of muscle strength, power, and balance, makes it a valuable tool in both clinical and research settings.^[11]

Although the 5×SqTST has gained recent attention as a functional assessment tool, evidence remains limited regarding its reliability and sensitivity in identifying lower-limb functional deficits. By simulating daily movements, the test provides meaningful insights into physical capacity and potential mobility risks. In the current study, we examined the 5×SqTST, an emerging functional performance assessment that has gained recent attention in the literature.^[11] While the 5×SqTST reflects a more dynamic, sport-oriented variation of lower-limb functional testing, the more widely recognized and validated measure remains the 5×STS.^[13] The 5×STS has been extensively studied and is commonly employed to evaluate lower-extremity strength, balance, and mobility, particularly among older adults and individuals with neurological or orthopedic impairments.^[13-16]

Despite their similarities, the squat-to-stand variant may impose greater neuromuscular demand, making it potentially more suitable for assessing younger or athletic populations.^[11] However, given the limited body of evidence supporting the 5×SqTST, future studies are warranted to establish its reliability, validity, and responsiveness across various populations. In the interim, clinical interpretation of 5×SqTST results should be cautiously guided by existing 5×STS literature.^[13,17]

The utility of the 5×SqTST extends beyond healthy populations, serving as a quick, equipment-free tool for identifying functional deficits across clinical and athletic settings. Its use can support early detection of reduced muscle power, aiding in targeted rehabilitation planning. Integrating such assessments into routine care enhances holistic evaluation of strength, power, and mobility. Schoenfeld et al.,^[6] highlighted the importance of balancing training variables according to performance-specific goals.

Isokinetic assessment of lower-extremity function offers a precise and objective method for evaluating muscular performance across standardized movement velocities.^[18] Typically, an angular velocity of 60°/s is employed to assess maximal muscle strength, while 240°/s is used to evaluate muscular strength and power under conditions that more closely mimic dynamic, functional movements.^[7,19] This form of testing is especially useful for identifying muscle imbalances, monitoring rehabilitation progress, and developing individualized exercise interventions. Although Vargas et al.,^[19] assessed muscle performance at an angular velocity of 240°/s, the current study utilized an angular velocity of 180°/s. Despite this difference, both velocities are commonly employed in isokinetic testing to evaluate muscle power and thus remain comparable within the context of neuromuscular performance assessment. Furthermore, significant variations in isokinetic outcomes were observed across testing velocities regardless of leg dominance.^[7,20] Torque-related parameters, including peak torque and Nm, were consistently higher at the slower angular velocity of 60°/s, whereas average power was substantially greater at 180°/s. These findings align with the well-established force–velocity relationship, wherein muscles produce greater force at slower contraction speeds and generate higher power output at faster velocities, reflecting physiological adaptations in muscle performance.^[20-22] Kabacinski et al.,^[23] have emphasized the importance of assessing quadriceps peak torque during concentric isokinetic testing at 60°/s and 180°/s to identify and compare strength asymmetries between the involved and uninvolved knees in female athletes.

The significantly greater average power observed at 180°/s highlights the critical role of movement velocity in enhancing power output, despite a concomitant reduction in torque. The high reproducibility and sensitivity of isokinetic testing to detect subtle neuromuscular deficits reinforce its status as a gold standard for assessing lower-extremity performance in both clinical and sports science settings.^[19,24]

Lutz et al.,^[7] reported that conventional hamstring-toquadriceps (H:Q) ratios varied significantly across different angular velocities but did not differ between dominant and non-dominant limbs. These findings highlight the impact of testing velocity on isokinetic outcomes, suggesting that performance differences are more closely linked to velocity-specific neuromuscular factors than to limb dominance. This supports the use of velocity-specific reference values when interpreting H:Q ratios in clinical and athletic contexts.^[8,9,25]

The 5×SqTST is a functional assessment, primarily evaluating dynamic balance and postural control during task-specific movements, whereas isokinetic dynamometry is a clinical assessment designed to quantify muscular strength, endurance, and power. Together, these complementary methods provide a well-rounded view of lower-extremity performance, aiding accurate assessment and guiding targeted interventions.^[26]

In addition, the analysis revealed no statistically significant differences between recreationally active and inactive participants in either functional or isokinetic outcomes. This may suggest that in a relatively homogeneous sample of healthy females, self-reported recreational activity status may not substantially impact functional performance. These findings collectively reinforce the clinical value of incorporating functional tests, such as the 5×SqTST, as a practical tool for assessing lower-limb performance in both research and practice.

Several limitations should be considered. First, the relatively small sample size, particularly the imbalance between recreationally active and inactive participants, may limit the generalizability of the findings. Second, the cross-sectional design limits any inference of causality between functional performance and isokinetic outcomes. This study’s focus on healthy female college students limits the generalizability of its findings. Third, we acknowledge the need for future research to establish the psychometric properties of the 5×SqTST. Future research should include larger, more diverse populations and adopt longitudinal designs to validate these results better and further investigate the predictive value of functional assessments.

CONCLUSION

The 5×SqTST shows strong promise as a practical and accessible proxy for assessing lower-limb muscle performance, particularly in contexts where isokinetic testing capabilities are lacking. Moderate negative associations between longer 5×SqTST completion times and reduced isokinetic power at 180°/s highlight its potential as a functional indicator of lower-limb strength. Owing to its simplicity and minimal equipment needs, the test is well-suited for both clinical and field settings. These results support the utility of the 5×SqTST in evaluating healthy young adults and guiding performance monitoring and intervention strategies. Additional studies are needed to validate its applicability across broader populations and to develop predictive models that integrate functional and laboratory-based assessments further.