EFFECTS OF CONCENTRIC VS. ECCENTRIC RESISTANCE TRAINING ON SINGLE MUSCLE FIBER MHC DISTRIBUTION IN YOUNG MEN

Abstract

PURPOSE: The purpose of this investigation was to determine the effects of a concentric vs. eccentric short-term resistance training program on single muscle fiber myosin heavy chain (MHC) distribution in humans. METHODS: Fifteen sedentary, healthy males were divided into three groups: concentric training (CTG) (n = 6, 24.2 ± 1.7 y, 181 ± 2 cm, 82.5 ± 4.6 kg), eccentric training (ETG) (n = 6, 23.7 ± 1.6 y, 178 ± 3 cm, 90.4 ± 6.1 kg) and control (CTL) (n = 3, 23 ± 1.5 y, 181 ± 2 cm, 97 ± 13.2 kg). The subjects performed 4 sets of 8 unilateral repetitions starting at 80% of concentric 1-RM, 3 days/week for a total of 4 weeks. Subjects were tested pre- and post-training for concentric 1-RM. Muscle biopsies were obtained from the vastus lateralis pre- and post-training for determination of single fiber MHC isoform distribution using SDS-PAGE/silver staining (100 fibers analyzed/subject pre- and post-training). Fibers expressing more than one MHC isoform (i.e., hybrid fibers) were analyzed for relative MHC isoform proportions via densitometry. RESULTS: The training program resulted in a 19% 1-RM strength gain for CTG (p < 0.05), and no change in ETG or CTL. MHC-IIx fibers decreased by 7% in CTG (p < 0.05) and ETG had an 11% increase in total hybrids (MHC-I/IIa+MHC-I/IIa/IIx+MHC-IIa/IIx) (p < 0.05). No other differences were noted in MHC distribution in the 3 groups. Densitometry analysis of hybrid fibers showed no change in relative MHC isoform proportions pre- to post-training for any group. CONCLUSION: After 4 weeks of concentric vs. eccentric resistance training the MHC distribution did not change dramatically and appears to have contributed little to the change in whole muscle strength. Supported partially by a Ball State University Graduate Research Award