Severe endurance training fails to change myosin heavy-chain distribution of diaphragm.

Histochemical analysis by Green et al. (1989) revealed that severe endurance training caused a transformation from type IIA to type IIB fibres in the costal diaphragm region of the rat. With the use of the electrophoretic method, in the current study, it was re-examined whether such a change was brought about in this respiration muscle. The animals were capable of running for 240 min/day at 40 m/min during the final phase of a 16-week training program. Four heavy-chain (HC) isoforms were separated by a single percentage polyacrylamide gel electrophoresis of extracts from muscles. Densitometric analysis of these HC isoforms revealed that exercise training failed to change the relative distribution of any HC isoforms in the diaphragm.