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Purpose: Despite the widely accepted benefits of exercise on chronic disease risk, controversy remains on the role of exercise in weight loss. This study examined the effect of different exercise types on measures of adiposity across different fat categories.

Methods: A total of 348 young adults (49% male; 28 /- 4 yr), participating in an ongoing observational study provided valid data over a period of 12 months. Fat mass (FM) and lean mass (LM) were measured via dual x-ray absorptiometry every 3 months. Percent body fat was calculated and used to differentiate between normal-fat, "overfat," and obese participants. At each measurement time point, participants reported engagement (min[middle dot]wk-1) in aerobic exercise, resistance exercise, and other forms of exercise.

Results: Most participants (93%) reported some exercise participation during the observation period. Total exercise or specific exercise types did not significantly affect subsequent body mass index after adjusting for sex, ethnicity, age, and baseline values of adiposity and exercise. Resistance exercise affected LM (P < 0.01) and FM (P < 0.01), whereas aerobic exercise only affected FM (P < 0.01). Any exercise type positively affected LM in normal-fat participants (P < 0.04). In overfat and obese participants, FM was reduced with increasing resistance exercise (P <= 0.02) but not with aerobic exercise (P >= 0.09). Additionally adjusting for objectively assessed total physical activity level did not change these results.

Conclusions: Despite the limited effects on body mass index, exercise was associated with beneficial changes in body composition. Exercise increased LM in normal-fat participants and reduced FM in overfat and obese adults. Adults with excess body fat may benefit particularly from resistance exercise.

(C) 2015 American College of Sports Medicine