Training affects myosin heavy chain phenotype in the trapezius muscle of women

The aim of this investigation was to determine whether 10 weeks of three di fferent types of training can alter the myosin heavy chain (MyHC) compositi on of the trapezius muscle. Twenty-one women were randomly assigned to thre e training groups that performed strength (n=9), endurance (n=7) or coordin ation training (n=5). Pre and post biopsies were taken from the upper part of the descending trapezius muscle and were analysed for MyHC isoform conte nt using 5% gel electrophoresis. In addition, we have studied the expressio n of embryonic and neonatal MyHCs using double-immunofluorescence staining. In the strength-trained group, there was a significant increase in the amo unt of MyHC IIA and a significant decrease in the amount of MyHC IIB and My HC I. In the endurance group, there was a significant decrease in the amoun t of MyHC IIB. MyHC composition in the coordination group was not altered. Following the training period, myotubes and individual small-sized muscle f ibres were observed in the strength and endurance trained groups. These str uctures were stained with the markers for early myogenesis (MyHC embryonic and neonatal). These data suggest that specific shifts :ln MyHC isoforms oc cur in the trapezius muscle following strength and endurance training. The presence of small-sized muscle fibres expressing the developmental isoforms of MyHC suggests that strength and endurance training induced the formatio n of new muscle fibres.