Author/Editor		Strojnik, V; Komi, PV
Title		Neuromuscular fatigue after maximal stretch-shortening cycle exercise
Type		članek
Source		J Appl Physiol
Vol. and No.		Letnik 84, št. 1
Publication year		1998
Volume		str. 344-50
Language		eng
Abstract		To examine some possible sites of fatigue during short-lasting maximally intensive stretchshortening cycle exercise, drop jumps on an inclined sledge apparatus were enalyzed. Twelve healthy volunteers performed jumps until they were unable to maintain jumping heigh >90% of their maximum. After the workout, the increases in the blood lactate concentration and serum creatine kinase activation were statistically significant (P < 0.001 and P < 0.05, respectively) but rather small in physiological terms. The major changes after the workout were as follows: the single twitch was characterized by smaller peak torque (P < 0.05) and shorter time to peak (P < 0.05) and half-relaxation time (P < 0.01). The double-twitch torque remained at the same level (P > 0.05), but with a steeper maximal slope of torque rise (P < 0.05); during 20- and 100-Hz stimulation the torque declined (both P < 0.01) and the maximal voluntary torque changel nonsignificantly but with a smaller maximal slope of torque rise (P < 0.01) and a higher activation level (P < 0.05), accompanied by an increased electromyogram amplitude. These findings indicate that the muscle response after the short-lasting consecutive maximum jumps on the sledge apparatus may involve two distinct mechanisms acting in opposite directions: 1) The contractile mechanism seems to be potentiated though a shorter Ca2+ trnsient and faster cross-bridge cycling, as implied by twitch changes. 2) High-frequency action potential propagation shows an impairment, which is suggested as the possible dominant reason for fatigue in exercise of this type.
Descriptors		MUSCLE FATIGUE MUSCLE CONTRACTION ELECTRIC STIMULATION EXERTION KNEE JOINT REFLEX, STRETCH ADULT PHYSICAL ENDURANCE ELECTROMYOGRAPHY LACTATES