Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: influence of training.
The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis of a group of male sprint athletes (n = 6) was analysed, before and after a three months period of intensive strength- and interval-training, using a sensitive gel electrophoretic technique. Significant improvements were observed after training in almost all of a series of performance tests. After training the sprinters revealed a decrease in fibres containing only MHC isoform I (52.0 +/- 3.0% vs. 41.2 +/- 4.7% (mean +/- SE) (P < 0.05)) and an increase in the amount of fibres containing only MHC isoform IIA (34.7 +/- 6.1% vs. 52.3 +/- 3.6% (P < 0.05)). Fibres showing co-existence of MHC isoforms IIA and IIB decreased with training (12.9 +/- 5.0% vs. 5.1 +/- 3.1% (P < 0.05)). Only one out of 1000 fibres analysed contained only MHC isoform IIB. In contrast, a higher amount of type IIB fibres (18.8 +/- 3.6% vs. 10.5 +/- 3.9%, (P < 0.05)) was observed with myofibrillar ATPase histochemistry. The majority of histochemically determined type IIB fibres of sprinters seems therefore to contain both MHC isoforms IIA and IIB. Sprint-training appears to induce an increased expression of MHC isoform IIA in skeletal muscles. This seems related to a bi-directional transformation from both MHC isoforms I and IIB towards MHC isoform IIA.
Andersen
J L
JL
August Krogh Institute, University of Copenhagen, Denmark.
Klitgaard
H
H
Saltin
B
B
D000328:Adult; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000737:chemistry*; D018482:Muscle, Skeletal / Q000737:chemistry*; D009210:Myofibrils / Q000201:enzymology; D009218:Myosins / Q000032:analysis* / Q000378:metabolism*; D010806:Physical Education and Training; D012420:Running
D009218:Myosins