Age-Group Differences in Early-Phase Isokinetic Knee-Extension Torque, Muscle Activation, Dynamic Balance, and Neuromuscular Biomarkers in Men: An Exploratory Cross-Sectional Study

Rapid torque production may reveal age-group differences not captured by peak torque. This exploratory cross-sectional study included 83 men in their 20s (n = 20), 30s (n = 21), 40s (n = 22), and 50s (n = 20). Knee-extension torque at 180°/s was recorded 50, 100, 200, and 300 ms after onset and at peak. Interval-specific torque change, vastus medialis electromyography, Lower Quarter Y-Balance Test performance, serum C-terminal agrin fragment (CAF) and neurofilament light chain (NfL) were assessed. Absolute and body-weight-normalized torque differed at every fixed time and at peak (all p < 0.001). At 300 ms, absolute torque separated the 20s group from all older groups and the 30s and 40s groups from the 50s group; peak torque separated only the 20s group from older groups. Torque-change and EMG-amplitude differences were phase dependent. Y-Balance scores were lower in the 50s group than in the 20s and 30s groups. CAF was higher in the 40s group than in the 20s and 30s groups. NfL was excluded from quantitative group comparisons because 48 of 83 results (57.8%) were below the laboratory-reported lower limit of quantification (9.38 pg/mL). Fixed-time torque may complement peak torque, but the design and exploratory multiple testing preclude causal or longitudinal inference.