Recovery after intense chronic stimulation: a physiological study of cat's fast muscle

Adult cats were used to study the recovery of muscles that had become altered by long-term electrical stimulation. Chronic activation was delivered to the deafferented common peroneal nerve (no pain, no reflexes), and contractile properties were measured for peroneus longus muscle. After 4 wk of great daily amounts of treatment at moderately high pulse rates (30-40 Hz delivered during 50% of daily time), the peroneus longus became considerably weaker, demonstrated a longer time course of twitches and a slower rate of rise of tetanic force, and became less fatigable. Furthermore, its twitch-to-tetanus ratio decreased, and there was no longer any depression of electromyogram (EMG) amplitude during fatigue tests. After 4 wk of subsequent rest it was found that 1) twitch speed and maximum tetanic force had returned to nearly normal values, 2) fatigue resistance showed some return toward normal but was still significantly enhanced, and 3) no significant recovery had yet occurred of the altered twitch-to-tetanus ratio, the abolished EMG depression, or the slowed rate of rise of tetanic tension. During the poststimulation recovery period, the progressive increase of isometric twitch speed was not promoted by the administration of small daily amounts of high-rate stimulation (100-Hz bursts). The results support the conclusions that 1) the time course of recovery differs among physiological properties, 2) the EMG and force reactions that occur during a fatigue test are not strongly coupled, as demonstrated by the alterations of their relationship during poststimulation recovery, and 3) in cat's fast muscles, there is still no evidence for rate-specific effects of chronic stimulation on isometric twitch speed.