Similar effects of cooling and fatigue on eccentric and concentric force-velocity relationships in human muscle

The purpose of this study was to investigate the effects of muscle temperat ure and fatigue during stretch (eccentric) and shortening (concentric) cont ractions of the maximally electrically activated human adductor pollicis mu scle. After immersion of the lower arm in water baths of four different tem peratures, the calculated muscle temperatures were 36.8, 31.6, 26.6, and 22 .3 degrees C. Normalized (isometric force = 100%) eccentric force increased with stretch velocity to maximal values of 136.4 +/- 1.6 and 162.1 +/- 2.0 % at 36.8 and 22.3 degreesC, respectively. After repetitive ischemic concen tric contractions, fatigue was less at the lower temperatures, and at all t emperatures the loss of eccentric force was smaller than the loss of isomet ric and concentric force. Consequently, normalized eccentric forces increas ed during fatigue to 159.7 +/- 4.6 and 185.7 +/- 7.3% at 36.8 and 22.3 degr eesC, respectively. Maximal normalized eccentric force increased exponentia lly (r(2) = 0.95) when V-max was reduced by cooling and/or fatiguing contra ctions. This may indicate that a reduction in cross-bridge cycling rate cou ld underlie the significant increases in normalized eccentric force found w ith cooling and fatigue.