Metabolic cost of free weight circuit weight training

BACKGROUND: Free weight circuit weight training (CWT) classes are popular group exercise classes designed to improve aerobic capacity, body composition, and muscular strength and endurance. The purpose of this investigation was to determine the training intensity and caloric expenditure associated with free weight CWT. METHODS: Twelve males and eighteen females (age 25.1+/-6.6 years) participated in a Bruce treadmill test to measure VO2max (47.9+/-10.6 ml/kg min). Subjects subsequently performed a learning trial, exercising to a 14 minute video-taped free weight CWT sequence which included squats and upper body exercises performed consecutively. All subjects then completed two randomly assigned video exercise bouts with light resistance (LR = 1.4 kg for males and females) and moderate resistance (MR = 5.9 kg for females and 10.5 kg for males), loads recommended by instructors for sedentary and fit individuals, respectively.

RESULTS: Statistical analysis by RM ANOVA (p < 0.0036) revealed significant increases in absolute and relative VO2, HR, and energy expenditure at MR as compared to LR for males and females. Mean VO2 and caloric expenditure values at MR were 15.7+/-2.3 ml/kg min and 6.21+/-1.01 kcal/min for males and 13.5+/-1.4 ml/kg min and 4.04+/-1.45 kcal/min for females. Associated HR responses were 129.5+/-18.4 and 119.2+/-19.4 bpm for males and females, respectively. The training stimulus was < 32% VO2max, significantly below ACSM recommendations (50% VO2max) for improving cardiovascular fitness; HR criteria (60% HRmax), however were met. Free weight CWT performed with loads < or =10.5 kg may not provide a sufficient cardiovascular training stimulus.

CONCLUSIONS: HR should not be used to assess exercise intensity in these classes.