Callahan, D. M., Foulis, S. A., & Kent-Braun, J. A. (2008). Age-related fatigue resistance is contraction mode dependant. ACSM 55th Annual Meeting Indianapolis. Presentation number 1986.

This study tested the hypothesis that age-related fatigue resistance in the knee extensor muscles is related to contraction mode. Healthy, untrained young (age 21-33, M = 8; F = 8) and older (age 65-80, M = 8; F = 8) adults performed intermittent maximal isometric (five seconds duration, 50% duty cycle) and isokinetic (0.5 seconds, 25% duty cycle; 120 degrees/second) knee extensions for four minutes. Fatigue was expressed as the relative decline in force from baseline to the average of the final three contractions of the isometric, and final five contractions of the isokinetic protocol. Habitual physical activity level was determined by accelerometry for five days (mean counts per day). Preliminary analysis detected no gender effect, so data were collapsed by gender and analyzed.

The young and old groups were well matched for physical activity level. Fatigue differences were detected in the isometric protocol, with the older group having less fatigue than the younger group. In contrast, during the isokinetic protocol, no differences between groups were detected.

Implication. In activity-matched young and older adults, age-related fatigue resistance in the knee extensors depends on contraction mode, with the greater fatigue resistance in older persons observed during isometric contractions but not during dynamic contractions.

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