The purpose of this study was to investigate the effects of clenbuterol supplementation on chemical markers of muscle damage, which occurs during downhill treadmill running(16% decline, 30m/min, 1h), in 30 Sprague-Dawley rats. The rats were randomly divided into three groups. They were control group(CON), clenbuterol adminstration group(CB), and recovery clenbuterol adminstration group(RCB). The chemical markers examined in this study included metabolic enzymes such as creatine phosphokinase(CPK), lactate dehydrogenase(LDH) and hormones(testosterone and cortisol) in circulating plasma. In addition, plasma concentrations of glucose, insulin, leptin and lipids were also measured along with muscle mass, retroperitoneal fat mass, running time to exhaustion, two-way ANOVA followed by LSD post hoc tests were used to test possible group by treatment interactions, and the results were as follows: 1) With respect to plasma CPK, LDH activity, there were significant group and time main effects(p<.05 respectively), with no significant group by time interaction. 2) There was a significant group by time interaction for testosterone and cortisol levels, such that the RCB group had significantly higher values than the control and the RCB group at the 48-hr postexercise period. 3) There were no significant group differences in body weight changes, but respect to the ratio of hindlimb muscle mass to body weight, the CB and RCB groups had significantly higher values than control(p<.05). With respect to the ratio of retroperitoneal fat to body weight, treatment groups had significantly lower values than the control(p<.05). 4) With respect to plasma glucose concentrations, there were similar trends with plasma insulin concentrations. 4) With respect to glucose, plasma lipids, insulin, leptin and TG concentration the treatment group had a significantly lower than control group(p<.05). 5) With respect to run time to exhaustion, the control group had a significantly longer time than the CB, or the RCB group(p=.001). In conclusion, the finding that the RCB group had significantly lower CPK, LDH activities than the other groups suggests that RCB administration can attenuate CFK, LDH activity associated with muscle damage.