Does increased serum creatine kinase activity reflect exercise-induced muscle damage in rats?

To test a hypothesis that exercise-induced increase in serum creatine kinase activity and the concomitant necrotic muscle damage in unaccustomed rats may be interrelated phenomena, and that the first might largely be caused by changes in lymph flow, groups of rats were separately exposed to a swimming, combination of swimming and running, and running protocol. Their serum was then repeatedly analysed over a period of 72 h for creatine kinase activity, and their soleus and the red parts of quadriceps femoris muscles for beta-glucuronidase activity (damage marker) 72 h after the commencement of the experiment, i.e. at a moment when muscle damage is in the necrotic phase. The results clearly showed that serum creatine kinase activity may increase without concomitant muscle damage (swimming protocol) and that muscle damage may occur without a statistically significant increase in serum creatine kinase activity (running protocol). Swimming followed by running increased creatine kinase activity more strongly than the separate protocols. Muscle damage was of a similar magnitude after running and after the combined exercise. The present results indicate that serum creatine kinase activity in rodent exercise myopathy is an inadequate indicator of injury both quantitatively and qualitatively.