Effects of aerobic and/or resistance training on body mass and fat mass in overweight or obese adults

 Recent guidelines on exercise for weight loss and weight maintenance include resistance training as part of the exercise prescription. Yet few studies have compared the effects of similar amounts of aerobic and resistance training on body mass and fat mass in overweight adults. STRRIDE AT/RT, a randomized trial, compared aerobic training, resistance training, and a combination of the two to determine the optimal mode of exercise for obesity reduction. Participants were 119 sedentary, overweight or obese adults who were randomized to one of three 8-mo exercise protocols: 1) RT: resistance training, 2) AT: aerobic training, and 3) AT/RT: aerobic and resistance training (combination of AT and RT). Primary outcomes included total body mass, fat mass, and lean body mass. The AT and AT/RT groups reduced total body mass and fat mass more than RT (P < 0.05), but they were not different from each other. RT and AT/RT increased lean body mass more than AT (P < 0.05). While requiring double the time commitment, a program of combined AT and RT did not result in significantly more fat mass or body mass reductions over AT alone. Balancing time commitments against health benefits, it appears that AT is the optimal mode of exercise for reducing fat mass and body mass, while a program including RT is needed for increasing lean mass in middle-aged, overweight/obese individuals.

Keywords: aerobic training, body composition, exercise, obesity, resistance training

the benefits of regular exercise are well documented (1), but the rationale underlying the exercise mode recommendations for specific health benefits remains unclear due in large part to the sparse scientific data supporting these recommendations. Given that approximately two-thirds of U.S. adults are overweight or obese, clinicians require clear exercise guidelines based upon sufficient evidence from which to prescribe the most effective exercise plan (18).

Although professional organizations have historically focused exercise guidelines on endurance or aerobic training (AT) for weight loss and maintenance (14), recent guidelines and position statements targeting body weight reduction and maintenance have suggested that resistance training (RT) may also be effective for reducing fat mass (11). In some cases, guidelines may lead to misperceptions among clinicians, exercise professionals, and laypersons about the strength of the evidence regarding the effectiveness of RT for inducing weight and fat mass loss (11, 20, 32), leading the reader to believe that RT has been conclusively shown to reduce fat mass. However, a close examination of the published literature reveals that randomized controlled trials are inconclusive on this point (7, 9, 19, 23, 24, 26).

Given the imperative of reducing obesity rates, exercise guidelines must be based upon unequivocal evidence of specific relations between exercise mode and changes in body mass and fat mass. Interestingly, despite the prevalence of obesity and the existing multiple position stands promoting exercise for the treatment of obesity, there are few randomized trials that have directly compared the effects of sustained AT, RT, or a combination of the two (AT/RT) on fat mass in overweight and obese adults. Most of the published studies addressing RT and fat mass changes have compared RT to an inactive control group and not to AT. Furthermore, existing studies have not directly studied comparable amounts of AT and RT. Thus it remains to be determined whether a significant amount of RT will decrease fat mass in overweight and obese adults, whether AT or RT is more effective at fat mass reduction when exposure (time) is held constant, and whether a combination of aerobic and resistance training (AT/RT) provides additive improvements in body composition. The Studies of a Targeted Risk Reduction Intervention through Defined Exercise-Aerobic and Resistance Training (STRRIDE-AT/RT) study was designed, in part, to address the aforementioned questions in a large randomized comparative effectiveness research trial of primarily middle-aged overweight and obese men and women with cardiometabolic health risk.