[Fatigue-related changes in dynamic and static components of eccentric contraction of the gastrocnemius muscle in the narcotized cat].

Effects of wide-range fatigue were studied on transient and steady force components of eccentric contraction of cat gastrocnemius. Muscle was activated by distributed stimulation of dissected ventral root L7 with rate of 10/s per filament. Active muscle was stretched through trapezoidal ramp with different velocities (1.25, 2.5, 10 mm/s). Fatiguing sessions consisted of standard test repetitions every 2 minutes. Normalized transient and steady components of extra force (fresh-state value = 1) were respectively 0.77+/-0.04 and 0.78+/-0.02 at 30% muscle tension drop, 0.27+/-0.04 and 0.55+/-0.02 at 60% muscle tension drop. Both transient and steady components have equal shares in extra force of eccentric contraction during moderate fatigue (up to 30% muscle tension drop); further pronouncing of fatigue entailed diminution of transient component share and corresponding augmentation of steady component one. Falling phase of transient component was subjected to fatigue and velocity of preceding lengthening in similar manner. We are speculated that steady component as reflection of actin-myosin affinity improvement during muscle stretching is less exposed to fatigue than cross-bridge rate.