In the first study, 5 mature, unconditioned, Thoroughbred geldings performed an initial submaximal exercise test (UC) prior to any conditioning and a final test (C) following 8 weeks conditioning. Serum creatine kinase (CK) and aspartate aminotransferase (AST) activity were measured before and for 72 h after exercise. Plasma lactate concentration [La−] was used as an indicator of exercise conditioning. Serum CK and AST activity remained increased above pre-exercise levels from 0–24 h and 0–8 h post exercise, respectively. There was a time by conditioning interaction for AST, CK and plasma [La−] resulting in an attenuated response of each variable following exercise test C as compared to following exercise test UC. These results indicate that submaximal exercise can elevate serum AST and CK and that conditioning can attenuate these changes.
A second study using 8 mature Thoroughbred horses was conducted to evaluate the effect of 2 different types of exercise, short term high intensity (STHI) and repeated submaximal exercise (RS) on serum AST and CK activities. Serum AST and CK activities during the post exercise period were higher in response to the RS test compared to the STHI test.