Influence Of Muscle Action On Energy Expenditure

Abstract

PURPOSE: Previous studies have found the energy cost of eccentric exercise to be approximately 1/7 to 1/4 that of concentric exercise, but no study has directly compared concentric–and eccentric–only resistance exercise. Therefore, we compared energy expenditure between squats performed with concentric or eccentric muscle actions. METHODS: 12 healthy men (20.9±1.1yrs) with a BMI<26 performed three exercise protocols once weekly designed to compare energy expenditure between different muscle actions: concentric (CON), eccentric (ECC), and a trial incorporating both concentric and eccentric (BOTH). Subject’s 1RM was determined using a plate-loaded squat machine. Each protocol was randomly assigned in a counterbalanced order and required subjects to perform 4 sets of 10 reps with 50% of 1RM. Repetition speed (2sec), ROM, and rest intervals were identical across protocols. Expired air was collected continuously before (15min), during (12min), and after (30min) each exercise protocol using a metabolic cart. Data were analyzed using a two-way repeated measures ANOVA, with Fisher’s least significant difference (LSD) post hoc analyses wherever appropriate. RESULTS: Rates of energy expenditure (kcal·min-1) were significantly greater (p<0.05) during sets 1 through 4 of CON and BOTH compared to ECC (see Table). CON was also greater than BOTH for sets 2 and 4. After exercise, CON > ECC at +5 and +10min, and BOTH > ECC at +5min. Significant differences (p<0.05) in total energy expenditure (kcal) included CON (58.1±6.27) > BOTH (50.7±5.92) > ECC (40.9±3.33). CONCLUSION: When squats were performed with 2sec CON or ECC muscle actions and 50% of 1RM, the energy cost of ECC was 2/3 to 3/4 that of CON exercise, whereas previous studies have reported ECC was about 1/4 of CON. A possible explanation may be that slower muscle actions used in our study resulted in elevated energy cost of eccentric muscle actions due to increased time under tension.Table: No title available.