Initial contractions of a single-load fatiguing exercise provide a valid assessment of age-related differences in peak power

The "gold standard" for measuring peak muscle power outputs is a comprehensive torque-velocity assessment performed across a wide range of loads and contraction velocities. However, this approach requires multiple high-load efforts that place stress on the joints, is time-intensive, and is often impractical in large cohorts or in clinical populations such as very old adults. Furthermore, it remains unclear whether simplified protocols underestimate age- and sex-related differences in peak power. We compared peak knee extensor power derived from a torque-velocity assessment with that obtained from the initial 10 contractions of a single-load fatiguing task in young, old, and very old males and females. Thirty young (22.6 ± 2.2 yr, 15 females), 73 old (70.6 ± 4.7 yr, 33 females), and 16 very old adults (85.8 ± 4.2 yr, 9 females) completed a torque-velocity assessment (14 isokinetic velocities, 30-450°·s-1) and a 4-min dynamic fatiguing exercise task (1 isotonic load at 20% of maximal voluntary isometric contraction, 80 contractions). Peak power outputs were strongly correlated between protocols (P < 0.001, r = 0.962), and the estimated age-related declines in power did not differ between the torque-velocity and fatigue task in males (∼6.6 W·yr-1 vs. ∼6.5 W·yr-1, P = 0.639) or females (∼4.3 W·yr-1 vs. ∼4.2 W·yr-1, P = 0.736). Peak power outputs from the initial 10 contractions of the fatigue task were ∼13% lower compared with the torque-velocity assessment (P < 0.001). These findings indicate that a brief fatiguing exercise task provides a valid alternative to the torque-velocity assessment for determining peak power across age groups, while simultaneously measuring fatigability, a clinically and physiologically important neuromuscular characteristic.NEW & NOTEWORTHY The initial contractions of a single-load fatiguing exercise can determine peak power outputs, showing a strong correlation (r = 0.962) with a comprehensive isokinetic torque-velocity assessment in young, old, and very old males and females. This approach accurately captures the age-related differences in peak power while simultaneously quantifying fatigability. Although peak power is underestimated by ∼13% compared with the torque-velocity assessment, the approach offers a practical way to evaluate two important neuromuscular outcomes in a single task.