Effect of Varying Loads and Contraction Speeds during Circuit Training on Energy Expenditure

Abstract

Circuit training constitutes a high-intensity interval program commonly used as a component of interventions targeting weight loss. However, the exact loads and patterns of training that will maximize energy expenditure (EE) have yet to be fully determined. PURPOSE: To compare EE among circuit training protocols using different loads and contraction speeds in recreationally trained men and women. METHODS: Three women (21.25 ± 2.2 yr) and two men (19.5 ± 1.5 y) performed three circuit training protocols using pneumatic machines (Keiser Corp, Fresno, CA) in a randomized order. Subjects performed three circuits consisting of leg press, lat pull down, hip adduction, chest press, knee flexion, overhead press, and hip abduction using either high-load (80% 1RM) explosive contraction (HLEC), high-load, controlled contraction (2s) (HLCC), or moderate-load (50% 1RM) explosive contraction (MLEC). No specific rest intervals were given and subjects were instructed to move from one machine to the next as quickly as possible (MLEC=15.2±4.0s; HLCC=16.3±4.9s; HLEC=15.6±2.6s). Expired air was collected continuously for 15 min before, during, and 30 min post-exercise. RESULTS: No significant differences were detected by condition or gender for resting EE. There was a significant difference among conditions during Exercise (Ex) (p=.047, ηp2=.780). Post hoc analysis revealed that the HLCC produced significantly higher EE values than HLEC (Meandiff=-13.13, 95% CI [-21.98, -4.27], p=.017), with no significant difference between MLEC and HLCC or HLEC. During EPOC there was a significant condition by sex interaction (p=.012, ηp2=.773).When analyses were done by gender, for men a significant difference was seen favoring HLCC over MLEC (p=.027), and a trend favoring HLCC over HLEC (p=.061). For women, no significant differences were found. For EE during Ex and EPOC combined there was a significant difference by condition (p=.027, ηp2=.699). Post hoc analysis revealed that HLEC produced significantly lower caloric output than HLCC (Meandiff=-20.58, 95% CI [-37.38, -3.79], p=.028). CONCLUSION: Our results favor circuit training using HLCC; however, sample size must be increased before definitive conclusions can be drawn and arguably EE due to anaerobic sources should be determined.