COEXISTENCE OF MYOSIN HEAVY CHAIN-I AND CHAIN-IIA ISOFORMS IN HUMAN SKELETAL-MUSCLE FIBERS WITH ENDURANCE TRAINING

The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis was analysed by one-dimensional electrophoresis and immunoblotting in three groups of young men with distinct difference in physical activity patterns. No major co-existence of MHC isoforms was found in the group with some daily physical activity. In the very sedentary group, however, 19±5% (P<0.05) of the fibres exhibited coexistence of MHC type IIa and IIb. Further, in the endurance trained group co-existence of MHC type I and IIa was manifested in 36±4% (P<0.05) of the fibres. Disuse and extreme usage of muscle both give rise to an elevation in co-expression of MHC isoforms in single muscle fibres but of markedly different combination of isoforms. © 1990 Springer-Verlag.