Objective: The primary purpose of this study was to compare the effects of explosive versus slow contractions on the rate of energy expenditure during and after resistance exercise.
Methods: Nine men (20 ± 2.5 yr) performed three exercise protocols using a plate-loaded squat machine, and a no-exercise (CONTROL) session in a randomly assigned, counterbalanced order. Subjects performed squats using either two second (SLOW) or explosive concentric contractions (EXPL), but identical repetitions (8), sets (4), and loads (60% 1RM). A secondary objective was to compare high- versus moderate-intensity exercise. Thus, a third protocol was performed that also used explosive contractions, with heavier loads (80% 1RM) and six sets of four reps (HEAVYEXPL). Eccentric reps (2 s), work (reps × sets × load), range of motion, and rest intervals between sets (90 s) were identical among all three protocols. Expired air was collected continuously for 20 min before, during, and 1 h after exercise and for about 1.5 h during CONTROL. Blood samples (25 μL) were collected before, immediately after, and 15, 30, 45, and 60 min after each protocol, and these samples were analyzed for blood lactate (mM).
Results: Average rates of energy expenditure (kcal·min-1) were significantly greater (P ≤ 0.05) during (7.27 ± 2.00 > 6.43 ± 1.64 and 6.25 ± 1.55, respectively) and after (2.54 ± 1.44 > 2.38 ± 1.31 and 2.21 ± 1.08, respectively) EXPL compared with SLOW and HEAVYEXPL, despite significantly (P ≤ 0.05) greater blood lactate after SLOW.
Conclusion: Squat exercise using explosive contractions and moderate intensity induced a greater increase in the rate of energy expenditure than squats using slow contractions or high intensity in all subjects tested. Thus, by using explosive contractions and moderate exercise intensity, experienced recreational exercisers can increase their energy expenditure during and after resistance exercise, and this could enhance weight-loss adaptations.