TRANSMISSION FATIGUE AND CONTRACTION FATIGUE

Abstract

The results of indirect maximal stimulation at different frequencies of several circulated muscles of the cat were studied. The fatigue caused by frequencies of stimulation higher than about 30 per sec. is interpreted as due to a deficiency of transmission; that resulting from stimulation at low frequencies (below 20 per sec.) is interpreted as due to a deficiency of the contractile system. At frequencies between 20 and 30 per sec. "subliminal" transmission fatigue is present. Recovery from transmission fatigue is relatively prompt; that from contraction fatigue is slow. Transmission fatigue and contraction fatigue are independent phenomena. Contraction fatigue is more prominent in "fast" than in "slow" muscles. Transmission fatigue is discussed from the standpoint of Rosen-blueth and Morison''s theory of decrease of acetylcholine output. Contraction fatigue is attributed to metabolic changes at the muscles.