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.