Age-related changes in power output during repetitive contractions of rat medial gastrocnemius muscle.
Changes in isometric force, power output and relaxation rate have been measured during repetitive tetanic contractions in 2 groups of rats of different ages. During the first 5 contractions there were no differences between a young and mature group. In contrast to isometric force production, which decreased about 3% per contraction, power output initially increased to 108% of the power output in the first contraction. A greater reduction in power output and relaxation rate after the 5th contraction indicated a greater reduction of the cross-bridge cycling rate in the younger rats. ATP, phosphocreatine and lactate concentrations after the last contraction were not different between the age-groups. In contrast IMP production, which has been suggested may play a regulatory role during fatigue was twice as high in the young rats. Judged by isometric force production there is no age-related difference in fatiguability. However, profound differences were observed in power output, which indicates that quantification of fatigue as a loss of isometric force may be seriously misleading when considering the functional status of the muscle for normal dynamic contractions.
de Haan
A
A
Department of Exercise Physiology and Health Science, Faculty of Human Movement Sciences, Free University, Amsterdam, The Netherlands.
van Doorn
J E
JE
Sargeant
A J
AJ
D000199:Actins / Q000378:metabolism; D000375:Aging / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction; D009126:Muscle Relaxation; D009218:Myosins / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D000199:Actins; D009218:Myosins