Loads and movement speed affect energy expenditure during circuit resistance exercise

Circuit resistance training (CT) constitutes a high-intensity interval program commonly used to target weight loss; however, the loads and exercise patterns that maximize energy expenditure (EE) remain undetermined. We examined differences in EE among CT protocols using varying loads and contraction speeds in recreationally trained males and females. Seven males (age, 21.1 ± 0.5 years) and 8 females (age, 20.0 ± 0.9 years) performed 3 randomized CT protocols incorporating 3 circuits using heavy-load (80% 1-repetition maximum (1RM)) explosive (HLEC), heavy-load, controlled (2 s) (HLCC), and moderate-load (50% 1RM) explosive contractions (MLEC). Expired air was collected continuously before, during, and after exercise. Blood lactate was collected at rest, immediately postexercise, and 5 min postexercise. No significant differences were detected for resting EE; however, there was a significant difference among conditions during exercise (p = 0.034, η_p² = 0.229). Post hoc analysis revealed that MLEC produced significantly higher EE than HLCC, but not HLEC (p = 0.023). There was a significant difference among conditions for rate of EE during exercise (p = 0.003, η_p² = 0.361). Post hoc analysis revealed that HLEC produced a significantly higher EE rate than HLCC (p = 0.012) or MLEC (p = 0.001). A condition × sex interaction was seen for blood lactate changes (η_p² = 0.249; p = 0.024). Females produced significantly greater change for MLEC than HLEC (p = 0.011), while males showed no significant differences. Our results favor CT using MLEC for a higher EE during a full workout; however, the rate of EE was highest when using HLEC.