Objective: To determine whether exercise intensity effects a change in body composition.
Design/subjects: Twelve untrained, moderately overfat, weight-stable women were randomly assigned to a high-intensity (80% VO2max) or low-intensity (50% VO2max) exercise group. Subjects trained four times per week for 12 weeks in monitored sessions, with a duration sufficient to expend 300 kcal. During this time, subjects were instructed to maintain their normal diet and activity patterns.
Outcome measures: Pretesting and posttesting included measurement of height, weight, body fat (via hydrostatic weighing), seven skinfold sites, seven circumference sites, and VO2max.
Statistical analyses: Results were analyzed using the Student's t test and paired samples t test.
Results: Posttesting revealed no significant between-group differences for change in weight, percent body fat, fat mass, fat-free mass, sum of skinfold measurements, or sum of circumference measurements. Mean weight loss was 0.7 lb for the high-intensity group (P = .55) and 3.3 lb for the low-intensity group (P = .03). Hydrostatic data revealed that each group lost an identical amount of fat (5.0 lb), but the high-intensity group gained more than twice as much fat-free mass (4.3 vs 1.8 lb). The greater increase in fat-free mass by the high-intensity group explains why the low-intensity group had a greater absolute weight loss.
Applications/conclusions: This study suggests that fat loss is a function of energy expended rather than exercise intensity. Therefore, if fat loss is the goal and time is limited, persons should exercise safely at as high an intensity as tolerable to expend as much energy as possible during their allotted time.