The effect of training and detraining on muscle composition in the horse.

Abstract

Percutaneous needle biopsies were obtained from 6 limb muscles in 6 horses before and during a training program of 10 or 15 wk designed to involve both aerobic and anaerobic work. In a subsequent detraining period, biopsies were also taken after 5 and 10 wk. Samples were analysed biochemically for enzyme activity of lactic dehydrogenase (LDH), creatine phosphokinase (CPK), aldolase (ALD), citrate synthase (CS), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and for glycogen content. Fiber typing was carried out histochemically before and 10 wk after commencement of training. There was a significant increase in the percentage of high myosin ATPase activity pH 9.4/high oxidative (FTH) fibers with a corresponding decrease in high myosin ATPase activity pH 9.4/low oxidative (FT) fibers and low myosin ATPase activity pH 9.4/high oxidative (ST) fibers after 10 wk training. During training, enzyme activities increased progressively but at different rates with an approximate 2-fold increase in all of the enzymes except CPK by the end of the training period. Changes in all the muscles studied were similar. Glycogen content increased by .apprx. 33%, which was significant when all the muscles were considered together. A decrease in enzyme activity occurred after 5 wk detraining. At 10 wk a consistent but inexplicable increase in all enzyme levels, except CS again occurred. Training greatly increased the activity of enzymes involved in both aerobic and anaerobic metabolism.