Comparing Muscle Hypertrophy and Myosin Heavy Chain Content between Relative Intensity and Repetition Maximum Resistance Training

Abstract

Comparison of resistance training (RT) methodologies is a critical component of determining appropriate and specific recommendations for health and human performance. Repetition maximum (RM) training typically consists of performing each exercise to momentary failure, thus providing a RM each day of training. Relative intensity based on sets and repetitions (RISR) conversely uses a percentage of a maximum or estimated maximum, typically not leading to failure. PURPOSE: To compare 10-weeks RISR or RM resistance training on skeletal muscle fiber size and protein accretion in well-trained subjects. METHODS: Fifteen well-trained males (age = 26.9+3.9yrs, body mass = 86.2+12.1kg) participated in the study (RISR group, n=7; or RM group, n=8). Muscle biopsies of the vastus lateralis were sampled 72 hours before beginning the intervention and again 72 hours after the final training. The 10-week RT program consisted of several phases: strength-endurance, maximum strength, a planned overreach, and a taper. The RM group achieved a daily maximum in each lift while the RISR group used a variety of submaximal training loads not leading to muscular failure. Workloads measured by volume load were similar between groups (p>0.05). A 2x2 mixed design ANOVA and effect size using Hedge’s g were performed for Type I cross-sectional area (CSA), Type II CSA, myosin heavy chain (MYH)1, MYH2, and MYH7. RESULTS: RISR significantly increased Type I CSA (p = 0.018) and Type II CSA (p = 0.012). None of the MYH proteins reached statistical significance for either group (p>0.05). Between-group effect sizes favored the RISR group for all variables: Type I CSA g=0.48, Type II CSA g=0.50, MYH1 g=0.31, MYH2 g=0.87, and MHY7 g=0.59. CONCLUSIONS: These results suggest RT utilizing a RISR approach may provide superior intramuscular outcomes compared to RM training in higher level lifters.