Myosin Heavy Chain Characteristics and Their Relationship to Exercise Performance

Abstract

There are a large variety of factors that affect performance in physical tasks. One factor is the muscle myosin heavy chain (MHC) composition of the muscle involved in the task. Differences in MHC can affect not just exercise performance, but can be related to general health. Purpose: The purpose of this study was to examine the relationship between exercise performance and MHC composition. Methods: Forty two (n=42) males of a variety of training backgrounds (aerobically trained, resistance trained, recreationally trained, and sedentary) took part in this study (Age = 22.4±3.5 years, Height 1.78±.07m, Weight 78.7±13.3 kg). Subjects were familiarized with vertical jumps, as well as maximal and fatiguing leg extensions during their first visit. A DEXA scan was performed on each subject along with thigh girth and skinfold caliper measurements. The following visit, subjects performed 2 reps of the following jump variations: counter movement jump, with and without arm swing, and depth jumps. Each jump was recorded utilizing a 2 dimensional force plate. Subjects then were tested for leg extension one repetition maximum (1RM). During the final testing session, subjects performed maximal velocity leg extensions at 30, 40, 50, 60, 70, 80, and 90% of their 1RM. Subjects then performed 15 maximal velocity repetitions at 70% of their 1RM on a cadence. Each rep of leg extension performance was recorded for velocity and torque. Immediately afterwards, a muscle biopsy was taken from the vastus lateralis that would be analyzed for MHC content utilizing SDS-PAGE separation (IIX = 13.8±12.9%, IIA =49.5±10.3 %, I = 36.8±11.3%). Data analysis of vertical jump and leg extension performance was analyzed for a number of variables. Results: Significant relationships were found between jump peak and mean power relative to cross sectional area of the thigh with type IIX fiber (r = .429-.459*)(* = significance p <.05). Negative relationships were noted with vertical jump height and type I fiber (r=-.355*), velocity load slope and intercept to type IIA fiber (r=.377-.480*), predicted peak and mean power maximum to type IIA (r=-.328-.352*) and type I fiber (r=.314*), and mean velocity fatigue index to IIA fiber (r=-.319*). Conclusion: This research further establishes a number of links joining exercise performance to muscle MHC, and promotes further research linking muscle MHC to performance at varying resistance levels along the potential load spectrum for skeletal muscle.