KINETIC EVALUATION OF MUSCLE DAMAGE DURING EXERCISE BY CALCULATION OFAMOUNT OF CREATINE-KINASE RELEASED

Kinetic evaluation of muscle damage during exercise by calculation of amount of creatine kinase released. Am. J. Physiol. 266 (Regulatory In tegrative Comp. Physiol. 35): R434-R441, 1994. - To quantify the exten t of muscle alteration during prolonged exercise, the release rate of creatine kinase (CK) from striated muscle was measured in six horses d uring a rest period (6 h) and during three exercise tests (15, 30, and 60 km) at a constant speed of 200 m/min. CK clearance was measured af ter intravenous bolus administration (150 U/kg) of a CK solution obtai ned from horse muscle. The CK steady-state volume of distribution was 0.059 +/- 0.0215 l/kg, the terminal half-life was 123 +/- 28 min, and the plasma clearance was 0.36 +/- 0.10 ml.kg(-1).min(-1). After an int ramuscular CK administration, the CK systemic availability was 74.1 +/ - 21.2% and the half time of absorption was 9.4 +/- 5.7 h, indicating a slow process for CK transit through the lymphatic system. The CK rel ease rate was only significantly increased during the 60-km exercise t est. The increase of CK plasma activity was observed after a delay of similar to 5 h and peaked after the end of the race; the estimated CK release rate was 9.92 +/- 2.62 U.kg(-1).h(-1) over a mean duration per iod of 65.8 +/- 15.8 h. With the CK activity of horse striated muscle taken into account, a 60-km race released a quantity of CK correspondi ng to an equivalent of 18.8 +/- 4.3 g striated muscle. It is concluded that the equivalent amount of damaged muscle may be considered as neg ligible for a 60-km test and that only very high plasma CK activity le vels (at least higher than 10,000 U/1) may provide some evidence of a myolysis.