Force deficits and breakage rates after single lengthening contractions of single fast fibers from unconditioned and conditioned muscles of young and old rats

摘要

Both contraction-induced injury and fatigue contribute to the force deficit observed immediately after muscles of humans (13, 38), rats (1, 47, 48), or mice (9, 33) have been stretched repeatedly during maximum, or near maximum, activation. The recovery from fatigue occurs within the first hour (33), but depending on the severity of the contraction-induced injury, the force deficit may persist for weeks (33), or even longer (5, 41, 42). For investigations of lengthening contraction-induced injury, the confounding factor of the contribution of fatigue to the magnitude of the force deficit during repeated contractions is eliminated by protocols of single stretches of maximally activated whole muscles (9, 10). Such protocols may also be replicated with single stretches of maximally activated perme-abilized single fibers from mice (6, 7), rats (25, 30, 31), or humans (46).