Title: Determining the Optimal Load to Increase Energy Expenditure with Explosive Resistance Exercise
Abstract: While energy expenditure with traditional resistance exercise has been shown to increase proportionally with the load, the influence of load on energy expenditure during maximally explosive resistance exercise is less clear. PURPOSE: This study assessed the influence of different loads on energy expenditure when using explosive concentric muscle actions. METHODS: Seven resistance-trained men (23±5yrs) performed squats and bench press with maximally explosive concentric muscle actions on three different weeks using 48, 60 and 72% of 1-RM in a randomized, counterbalanced order. The eccentric (2s) and concentric (∼1s) repetition (rep) speeds, ROM and rest intervals (90sec) were identical between protocols. Sets, reps and loads were chosen so that total work performed was identical: LIGHT48, was 4 sets of 10 reps; MODERATE60 was 4 sets of 8 reps; and HEAVY72 was 5 sets of 5 reps. On the day of each trial, subjects consumed identical meals for breakfast and lunch. Expired air was collected continuously before (15min), during (∼17 to 23min), and after (1hr) each protocol. RESULTS: Average rates of energy expenditure were significantly greater during squat and bench press and 5min after LIGHT48 and MODERATE60 compared to HEAVY72 (p<0.05). Average rates of energy expenditure were also greater during squat and bench press with LIGHT48 compared to MODERATE60. When adjusted for differences in duration, total energy expenditure was 221±18, 213±21, and 215±16 kcal for LIGHT48, MODERATE60 AND HEAVY72, respectively. However, even though total work was identical for each protocol, the work per set was lower for HEAVY72. Thus, we had the subjects perform another 72% of 1-RM trial with 4 sets of 6.5 reps (HEAVY72B), but with the work per set matched as closely as possible. Total energy expenditure for HEAVY72B was 218±20 kcal, which was more similar to LIGHT48. But, the HEAVY72B protocol was extremely difficult to complete. CONCLUSION: Light training loads (45-50% of 1-RM) may be preferred for enhancing energy expenditure responses with explosive resistance exercise because heavier loading requires a smaller work to rest ratio per set, which lowers the efficacy of the workout. Supported by University Student Academic Research Award and Dept. of Health, PE & Human Performance, Salisbury University.