Running-induced muscle injury and myocellular enzyme release in rats.

The relationships and time course of exercise-induced muscle damage, estimated by beta-glucuronidase activity and microscopy, to muscle swelling, estimated by muscle water content and microscopy, and to the serum activity of creatine kinase (CK) and the concentration of carbonic anhydrase III were studied in rats 2, 12, 48, and 96 h after 90 min of intermittent running uphill (+13.5 degrees) or downhill (-13.5 degrees) at a speed of 17 m/min. The injury was more pronounced in soleus after uphill running and in the red parts of quadriceps femoris and in the white part of vastus lateralis after downhill running, whereas triceps brachii was not damaged. Increase in muscle water content preceded the increase of beta-glucuronidase activity. Both running protocols similarly increased serum CK 2 h postexercise. After downhill running a second peak in serum CK was observed 48 h later. The CK changes were not in concert with the changes in muscle water content or beta-glucuronidase activity, suggesting that these responses may not be mechanistically (or causally) related.