GREGOREVIC, P., D. A. WILLIAMS, and G. S. LYNCH. Hyperbaric oxygen increases the contractile function of regenerating rat slow muscles. Med. Sci. Sports Exerc., Vol. 34, No. 4, pp. 630–636, 2002. Human trials of hyperbaric oxygen (HBO) treatment of sports-related muscle injuries are equivocal. Although most human skeletal muscles are composed of mixed muscle fiber types, it is unclear whether HBO affects fiber types differently.
Purpose: We tested the hypothesis that HBO can enhance the functional properties of regenerating rat soleus muscles that are composed predominantly of slow fibers.
Methods: After intramuscular injection of bupivacaine hydrochloride to induce the degeneration of all fibers within the soleus muscle, treated rats received daily HBO treatment at 3 atmospheres absolute.
Results: In untreated rats, injured muscles demonstrated a reduced force-producing capacity (control soleus vs injured soleus, 220.3 ± 2.5 vs 157.6 ± 3.3 kN·m−2 at 25 d postinjury, respectively, P < 0.05) and contained smaller regenerating muscle fibers than uninjured soleus muscles (fiber cross sectional area in control soleus vs injured soleus, 2289 ± 164 vs 1154 ± 92 μm2 at 25 d postinjury, respectively, P < 0.05). The regenerating soleus muscles of HBO-treated rats demonstrated a greater force-producing capacity as a percentage of contralateral control muscles than the regenerating muscles from untreated rats at 14 d postinjury (regenerating HBO-soleus peak tension and untreated soleus peak tension, 42.9 ± 1.9 and 35.8 ± 3.9% of contralateral control muscles, respectively, P < 0.05), but no effect of treatment was observed at 25 d postinjury.
Conclusion: HBO enhanced the contractile properties of regenerating rat soleus muscles after myotoxic injury, but this improvement was not sustained for the duration of the regenerative process. The data indicate that the outcome of HBO treatment of a muscle injury may be influenced by the fiber type composition of the injured muscle.