Changes in myosin heavy chain composition with heavy resistance training in 60-to 75-year-old men and women

The purpose of this investigation was to assess the myosin heavy chain (MHC ) expression in the vastus lateralis muscle from elderly men and women, and to determine whether heavy resistance training influences its expression. Twenty healthy, mildly physically active subjects gave their informed conse nt to participate in the study. The experimental group consisted of seven m en and seven women [mean (SD) age 65.5 (4.1) years] and the control group c onsisted of three men and three women [mean (SD) age 62.3 (3.6) years]. The 6-month resistance training program was divided into two phases with weeks 1-12 consisting of high-intensity resistance training, and weeks 13-24 inv olving power training. Muscle biopsy samples were taken from the vastus lat eralis muscle at week 0 and week 24 using the needle biopsy technique. The male and female experimental groups both exhibited a significant decrease ( P less than or equal to 0.05) in the percentage of MHC IIb, while the exper imental female group also demonstrated a significant increase (P less than or equal to 0.05) in the expression of MHC IIa, after 24 weeks of heavy res istance training. There was no change in MHC expression within the control group. The male [130.4 (25.3) kg vs 171.1 (30.5) kg] and female [58.2 (8.3) kg vs 77.9 (11.1) kg] experimental groups exhibited a significant increase (P less than or equal to 0.05) in the maximal strength values for the 1 re petition maximum (1RM) squat exercise. The control group showed no change i n strength for the 1RM squat exercise for either the male [115.8 (35.10 kg vs 123.8 (47.2) kg] or female [57.5 (99.0) kg vs 58.3 (2.9) kg] groups. The results clearly show that elderly subjects undergoing heavy resistance tra ining have the ability to produce a similar shift in the expression of MHC isoforms from MHC IIb to MHC IIa, as has been shown to occur in younger sub jects. This highlights the plasticity of human skeletal muscle in response to heavy resistance training, even at older ages.