The Relationship Between Lower-Limb Muscle Strength and Related Parameters With Vertical Jump in Young Adult Males

This cross-sectional observational study is designed to comprehensively analyze the relationship between high-volume isokinetic muscle performance and explosive vertical jump capacity in healthy, recreationally active young adult males.

While traditional neuromuscular assessments frequently emphasize momentary peak force (Peak Torque), this study investigates the hypothesis that sustained mechanical work capacity (Total Work) and fatigue resistance (Fatigue Index) are more robust predictors of complex explosive tasks such as the countermovement jump (CMJ).

Methodology and Testing Protocol:

Participants will complete all assessments in a single laboratory session under controlled environmental conditions. The standardized testing sequence is as follows:

1. Anthropometric and Body Composition Assessment: Participants' height, body mass, and body fat percentage will be measured using a multi-frequency bioelectrical impedance analyzer (InBody 270) following standard manufacturer protocols.
2. Countermovement Jump (CMJ) Test: Following a standardized dynamic warm-up, participants will perform the CMJ test on a validated contact mat system (SmartJump). Participants will start from a standing position with hands placed on the hips to eliminate the influence of arm swing. They will perform a quick downward countermovement to approximately 90 degrees of knee flexion and execute a maximal vertical jump. Three trials will be conducted with a 30-second rest interval between attempts, and the highest jump will be recorded for analysis.
3. Isokinetic Muscle Strength and Fatigue Test: After a 5-minute cycle ergometer warm-up, participants will undergo isokinetic testing on a computerized dynamometer (Humac Norm). Following familiarization trials, participants will execute a high-volume fatigue protocol consisting of 50 continuous, maximal concentric knee flexion and extension repetitions at an angular velocity of 180°/sec for both legs.

Primary Variables Analyzed:

From the isokinetic protocol, the primary variables of interest include Peak Torque (Nm), Average Power (W), Total Work (Nm), and the Isokinetic Fatigue Index (%). These mechanical metrics will be statistically analyzed against the maximum CMJ height (cm) to evaluate the predictive strength of sustained mechanical work capacity versus momentary force production on explosive motor performance.