Ask the Experts on . . .
Resistance Training Vs Aerobic Exercise for Weight Loss
Although exercise is touted as an essential component of any health improvement program, often the type of exercise is not formally discussed. By default, many professionals and lay people consider aerobic exercise sufficient. I am of the impression that resistance exercise, also of moderate intensity, is essential for increasing metabolic rate and maintaining strength and flexibility. I suggest to my patients a protocol of at least 2 times per week of formal resistance training (in addition to at least 2 weekly sessions of aerobics). I would like to know your attitudes and experience regarding resistance training as part of an overall health improvement and weight loss program.
Nahum Kovalski, MD
from Josephine Conolly, 11/21/00
Although exercise is an important part of a health improvement and weight management program, its role in weight loss and maintenance of weight loss has been misunderstood and poorly portrayed in the lay literature. Exercise has the potential to influence weight loss and maintenance of weight loss due to the direct affects of increased energy expenditure, as well as indirect affects on body composition, resting metabolic rate, and dietary compliance.
The research in this area is surprisingly inconclusive and conflicting. This is likely due to the large number of variables influencing the process. These include absolute energy intake, energy intake relative to energy needs, intake of macronutrients (carbohydrates, proteins, and fats), total induced energy deficit, type of exercise, frequency and duration of exercise, and intensity of exercise. In addition, each individual responds differently to exercise.
Numerous studies examining the role of exercise in weight loss do not adequately control for these variables. Specifically, reviewed dietary intake was not individually prescribed or adequately monitored in many different studies. Therefore, as research in this area continues, clinical judgment and patient input will be essential to the development of meaningful exercise programs. Two studies will be reviewed to illustrate these points, and then the research in this area will be summarized.
Kraemer and colleagues demonstrated the difficulty in documenting positive affects of exercise. His group studied the effects of 12 weeks of dieting, dieting plus aerobic exercise, or dieting plus aerobic and resistance training. Subjects consumed approximately 1200 calories per day. Aerobic exercisers participated in 30-50 minutes of supervised training at 70% to 80% of functional capacity 3 times per week. Those participating in resistance training followed these aerobic exercise sessions with 11 resistance training exercises following heavy resistance training principles.
Participants in all groups lost a significant amount of weight compared with baseline (6.2 kg, 6.8 kg, or 7.0 kg, respectively) and significant amounts of body fat (5.8%, 8.0%, and 4.3%, respectively). However, there were no significant differences among the 3 treatment groups. There were also no significant changes in fat-free mass over the 12-week intervention in any of the groups, ie, no losses or gains of fat-free mass. This retention of fat-free mass, especially in the diet-only group, is inconsistent with many other reports in the literature, which indicate a loss of fat-free mass when dieting without exercise. The diet prescriptions most commonly used result in a diet-induced kilocalorie deficit greater than 500. Although the energy deficit created by the diets in this study are not directly reported, it can be estimated to be approximately 250-380 kilocalories per day. This deficit is relatively mild compared with many other studies, thereby preventing the breakdown of fat-free mass to support energy needs.
Ballor and colleagues studied the effects of 12 weeks of aerobic exercise or resistance training on retention of weight loss in patients who had recently lost an average of 9% of their body weight. Half of the participants trained aerobically at 50% functional capacity for 60 minutes 3 times per week. The other half participated in a progressive resistance training program 3 times per week. The resistance training group experienced no further weight loss, and there was a trend toward increased fat-free mass. On the other hand, aerobic exercisers experienced an average of 2.5 kilograms of additional weight loss, predominantly composed of body fat with a maintenance of fat-free mass. There were no significant changes in resting metabolic rate (absolute or relative to body mass), although there was an upward trend in absolute resting metabolic rate in weight trainers.
Although in theory aerobic and resistance training can facilitate weight loss through decreases in fat mass and retention of fat-free mass, the measurable impact is limited when performed in the amounts typically prescribed (3-5 times per week, 20-60 minutes, moderate to high intensity). This is most likely due to the large diet-induced calorie deficits in the majority of studies. The further reduction in calorie deficit associated with the exercise is typically small. Therefore, the contribution of exercise may be greater when the diet-induced calorie deficit is mild, when protein intake is adequate to support maintenance or increase in fat-free mass, and when the client can exercise more frequently for longer time periods.
The greatest impact of exercise is on the retention of weight loss. This is widely supported by the prospective and retrospective studies reviewed by Votruba and coworkers. Individuals who exercised experienced a significantly smaller amount of weight regain. In addition, a greater percentage of the weight regained was fat-free mass. Two hundred and ten minutes of exercise per week, such as brisk walking, appears to be the minimum amount needed to effectively limit average weight regain to 35% to 40%. The impact of exercise does appear to be dose dependent with 600 minutes of brisk walking per week associated with a weight regain of only 15%.
In summary, it is important to encourage patients to begin an exercise program to facilitate weight loss and to establish an exercise habit to more directly support maintenance of weight loss. Patients should be involved with the selection of the type of exercise, although there is some support in the literature for aerobic exercise to maximize fat loss. There are, of course, additional benefits of exercise in risk reduction for morbidities associated with obesity, such as a decrease in lipid levels and blood pressure.
Kraemer WJ, Volek JS, Clark KL, et al. Physiological adaptations to a weight-loss dietary regimen and exercise programs in women. J Appl Physiol. 1997;83:270-279.
Ballor DL, Harvey-Berino JR, Ades PA, Cryan J, Calles-Escandon J. Contrasting effects of resistance and aerobic training on body composition and metabolism after diet-induced weight loss. Metabolism. 1996;45:179-183.
Votruba SB, Horvitz MA, Schoeller DA. The role of exercise in the treatment of obesity. Nutrition. 2000;16:179-188.