Casey, A., Constantin-Teodosiu, D., Howell, S., Hultman, E., & Greenhaff, P. L. (1996). Metabolic response of type I and II muscle fibers during repeated bouts of maximal exercise in humans. American Journal of Physiology, 271, E38-E43.

Male Ss (N = 9) performed two 300 sec maximum efforts on an isokinetic cycle machine at 80 rpm. There was a 4 min recovery period between each effort.

The following were found:

• In bout 1, ATP and PCr utilization was greater in type II (anaerobic, fast-twitch) fibers than in type I fibers.
• During the 4 min recovery there was incomplete restoration of ATP and PCr in type II fibers but it was almost complete in type I fibers.
• During bout 2, there was reduced ATP and PCr utilization in type II fibers but not in type I fibers.
• Performance was significantly reduced in the second bout.

Implication. In very high intensity work that places great emphasis on explosive anaerobic work, the recovery of type II (fast-twitch) fibers associated with the work is slower than compared to type I (slow-twitch) fibers. This means recovery intervals between "sprint" or short intense activities have to be longer than those employed for endurance training. The slower recovery of type II fibers warrants greater rest periods.

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