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.
Research into the effects of ageing on muscle function. This work was carried out by Arnold de Haan (later Professor) as part of his PhD supervised by Professor Anthony Sargeant.
Age-related changes in power output during repetitive contractions of rat medial gastrocnemius muscle
Pflugers Arch. 1988 Oct;412(6):665-7