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

Male subjects (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 utilisation was greater in type II (anaerobic, fast-twitch) fibres than in type I fibres.

• During the 4 min recovery there was incomplete restoration of ATP and PCr in type II fibres but it was almost complete in type I fibres.

• During bout 2, there was reduced ATP and PCr utilisation in type II fibres but not in type I fibres.

• Performance was significantly reduced in the second bout.