Training for Weight Management
Len Kravitz, Ph.D. and Randy Malone, M.E.D
Attempts at solving the weight management puzzle have focused considerable attention on energy expenditure, caloric intake, energy balance and fuel utilization. RMR, which denotes the bulk of daily energy expenditure (~60-75%) depicts the energy used by the body to sustain bodily functions (Dolezal and Potteiger, 1998). Bodily functions engaging the RMR include nervous system activity, pulmonary function, cellular respiration and cardiovascular function. RMR is highly correlated to fat-free mass (muscle, bone, cartilage), and may be affected by body composition, gender, age and genetic factors. A decrease in RMR of 2% to 3% per decade with advancing age is primarily attributable to a loss in fat-free mass (Poehlman and Melby, 1998). In addition, it appears that males tend to have higher RMR than females, due chiefly to the larger body size.
Energy expended above RMR includes the thermic effect of feeding (food digestion and absorption processes), adaptive thermogenesis (shivering, postural adjustments, fidgeting), and the thermic effect of physical activity, which is the most variable component. Of great interest to personal trainers is the effect resistance training may have on RMR.
Resistance Training and RMR
Theoretically, increases in lean body mass should increase RMR and thus impact daily energy expenditure and body composition. Poehlman and Melby (1998) reviewed a number of studies that examined the effects of resistance training on lean body mass and RMR (See Table 1). Most investigations resulted in increases in fat-free mass while RMR increased moderately in a few studies. Although the exact mechanism of these changes is unknown, several factors may contribute including increases in protein synthesis, norepinephrine, and sympathetic nervous system activity.
Effects of Resistance and Endurance Training on RMR
A recent study by Dolezal and Potteiger (1998) examined the effects of concurrent endurance and resistance exercise on basal metabolic rate (BMR, which is very similar to RMR only using stricter measurement criteria), body composition, aerobic power, and muscular strength in 30 physically active males (20 yr of age). One group did only endurance training, while a second group did resistance training, and a third group did a combined resistance and endurance training. The BMR increased in the resistance training (6%) and combined training (5%) groups, whereas the endurance training group showed a decrease of 2%. Although this population of males had an initial lower than average percentage of body fat (%BF), reductions were observed. The pre- and post-training %BF results were as follows: resistance training (15.4% to 14%), endurance training (11.8% to 9.5%), and combined training (12.2% to 8.7%). The resistance training group showed the greatest gains in muscular strength, demonstrating increases in the 1RM for the bench press (24%) and parallel squat (23%) as compared to the combined training group’s bench press (19%) and parallel squat (12%). There was no observable change in muscular strength with the endurance exercise group. However, as expected the maximal aerobic power increased most dramatically in the endurance (13%) training group compared to the combined (7%) and resistance (-2%) training groups. These data indicate that endurance training will increase aerobic power and decrease body fat; resistance training will increase muscular strength, fat-free mass, and BMR; and a combination of these two training schemes provides benefits in all of these variables.
Prescribing Combined Endurance and Resistance Training
It is, of course, essential to consider the goals of an individual as well as their current fitness and health status when prescribing any type of exercise program. In light of the evidence of the benefits of combined endurance and resistance training, it seems that personal trainers and health professionals should take a two-fold approach when prescribing exercise if a goal for the client is weight management. Aerobic exercise will substantially enhance cardiovascular health and daily energy expenditure. Independently, resistance training will help to promote increases in fat-free mass, RMR (and BMR), and muscular fitness. While Dolezal and Potteiger (1998) utilized a schedule of aerobic and resistance training on the same days, it may be more beneficial (and certainly less time-consuming on a per day basis) to schedule the training programs onalternating days.
Table 1. Studies on Resistance Training and Resting Metabolic Rate
Author Subjects Training Fat Free Mass RMR
Broder et al., 1992 13 males 12 wks Incr. 2 kg None
Van Etten et al., 1995 21 males 12 wks Incr. 1.3 kg None
Pratley et al., 1994 13 older males 16 wks Incr. 1.6 kg Incr. 8%
Campbell et al., 1994 12 older males 12 wks Incr. 1.4 kg Incr. 7%
References:
Treuth et al., 1995 13 older females 16 wks No change Incr. 9%
Dolezal, B.A. and Potteiger, J.A. (1998) Concurrent resistance and endurance training influence basal metabolic rate in nondieting individuals. Journal of Applied Physiology, 85, 695-700.
Poehlman, E.T. and Melby, C. (1998) Resistance training and energy balance. International Journal of Sport Nutrition, 8, 143-159
International Journal of Sport Nutrition, 8, 143-159. |
