Achilles tendon rupture in athletes: histochemistry of the triceps surae muscle.

Bilateral percutaneous muscle biopsies of the triceps surae were analyzed in 12 athletes who had sustained a one-sided subcutaneous rupture of the Achilles tendon while practicing their main sport. No necrosis, atrophy, or significant fiber grouping or regeneration was evident. The soleus muscle in these athletes was composed of approximately 70% of type I fibers in both the noninjured and injured sides, and no significant differences were detected in their histochemical composition. Fiber areas were within described values and not significantly different between the two sides. The noninjured side revealed an insignificant trend to greater average capillary density and average capillary/fiber ratio. Muscle abnormalities do not appear to be a significant factor in determining Achilles tendon rupture in healthy athletes.