CHANGES IN THE MYOSIN HEAVY-CHAIN ISOFORM PROFILE OF THE TRICEPS BRACHII MUSCLE FOLLOWING 12 WEEKS OF RESISTANCE TRAINING

The purpose of this investigation was to determine whether 12 weeks of resistance training, which increased arm girth (5%) and forearm exten sor strength (39%), also altered the myosin heavy chain (MHC) characte ristics of the triceps brachii muscle. Fifteen healthy, active men vol unteered to participate under experimental (n = 11) or control (n = 4) conditions. The experimental group completed four sets of eight to 12 repetitions for each exercise (i.e. triceps pushdown, close grip benc h press, triceps kickbacks and biceps curl) with loads of between 70-7 5% of one repetition maximum (1RM) three times a week. The inter-set a nd inter-exercise recovery period was only 90 s. Skeletal muscle tissu e was removed from the triceps brachii muscle prior to (WO) and follow ing 4 (W4), 8 (W8) and 12 (W12) weeks of the investigation. Samples we re analysed for MHC isoform content using 6% sodium dodecyl sulphate-p olyacrylamide gel electrophoresis (SDS-PAGE). MHC isoform composition in the control group did not change significantly. However, the percen tage of MHC type IIb isoform decreased significantly from WO to W4 and again from W4 to W12 [WO: 39.7 (9.2); W12: 29.2 (8.2)%] in the experi mental condition. The increments in MHC type IIa [WO: 34.0 (9.9); W12: 41.5 (10.4)] and type I [WO: 26.3 (7.9); W12: 29.3 (9.6)] isoforms we re not significant for the experimental group. However, the effect siz e (ES) transformation of changes in types IIa MHC content was moderate (ES = 0.75). Changes in MHC isoform content were not significantly co rrelated with changes in 1RM strength for the triceps pushdown exercis e. These data indicated that resistance training rapidly, and in an on going manner, changed the contractile protein profile of trained skele tal muscle. However, changes in MHC isoform composition in the first 1 2 weeks of training were not implicated in the development of 1RM tric eps pushdown strength.