SKELETAL-MUSCLE CHARACTERISTICS IN 2-YEAR-OLD RACE-TRAINED THOROUGHBRED HORSES

Skeletal muscle samples were obtained by needle biopsy from two depths of the m. gluteus medius of 50, young race-trained thoroughbred raceh orses. Histochemical and biochemical characteristics of the muscle sam ples were analysed. Fibres were classified as type I, type IIa or type IIb on the basis of the pH dependent lability of the myosin ATPase re action. The activities of citrate synthase (CS) and glycogen phosphory lase (Phos) were determined. Muscle fibre composition varied markedly between deep and superficial muscle samples and this was reflected in differences in the activities of citrate synthase (CS) and phosphoryla se (Phos). CS activity was greater in samples taken from a depth of 90 mm (deep) than those taken from a depth of 40 mm (superficial: 122 +/ - 19 compared with 88 +/- 16 mu mol/g dry muscle/min at 25 degrees C). Phos activity was greater in superficial samples (137 +/- 20) compare d with deep samples (117 +/- 21). Regression analysis was used to esti mate the enzyme activities in the different fibre types. No significan t correlations were observed between histochemical and biochemical mea sures and subsequent racing performance.