Effects of exhaustive concentric and eccentric exercise on murine skeletal muscle.

C57BL/10SnJ mice were run to exhaustion on a treadmill at a 20 degrees incline, uphill or downhill. Contractility, morphology, and histology were evaluated in the soleus and extensor digitorum longus (EDL) muscles at days 0, 3, and 7 postexercise. Serum creatine kinase was elevated immediately postexercise (681% increase downhill and 225% increase uphill). After uphill running, the soleus had a significant increase in cross-sectional area (CSA) and decreased tetanic tension/CSA and twitch contraction time through day 7. The EDL showed increased CSA, decreased tetanic and twitch tension, and increased fatigue at day 0 only, with no other contractile abnormalities. After downhill running, the EDL showed reduced tetanic and twitch tension, but no fatigue or morphometric differences, whereas the soleus showed no significant abnormalities. No significant muscle histopathology was observed at any time following uphill or downhill running. This study indicates that both exhaustive eccentric and concentric exercise may produce significant impairments in muscle contractility without inducing histopathology. Exhaustive concentric exercise also induces muscle swelling and may preferentially impair slow twitch fibers.