Knee extensor fatigue resistance of young and older men and women performing sustained and brief intermittent isometric contractions.

INTRODUCTION: Susceptibility to muscle fatigue during aging could depend on muscle activation patterns.

METHODS: Young (mean age, 22 years) and older (mean age 70 years) men and women completed two fatigue tests of knee extensor muscles using voluntary and electrically stimulated contractions.

RESULTS: Older subjects displayed a shift to the left of the torque-frequency relationship and held a sustained voluntary isometric contraction at 50% maximal strength for significantly longer than young (P < 0.001). Young and old showed similar fatigue during electrically induced, intermittent isometric contractions (1-s on, 1-s off for 2 min), but women fatigued less than men (P = 0.001). Stronger muscles fatigued more quickly, and slower contractile properties were associated with longer sustained contractions.

CONCLUSIONS: The slowing and weakness of older muscle was associated with superior fatigue resistance during sustained isometric contractions. Young and old showed similar fatigue following a series of brief, intermittent contractions, but women fatigued less than men.