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Strength and Conditioning Journal: Vol. 24, No. 1, pp. 65–69.
The Role of Resistance Exercise in Weight Loss
Jeffrey L. Alexander, MS
Arizona State University-East
What Is the Role of Weight Training in Weight Loss?
SUCCESSFUL WEIGHT LOSS IS achieved through the creation of a negative energy balance, wherein the amount of energy taken in is less than the amount burned or utilized through physical activity and/or exercise. There are 2 factors to energy balance: energy intake and energy expenditure. Weight loss can only be achieved through modifying one or both of these factors. The focus of this report is on energy expenditure, keeping in mind that any reduction in energy intake will add to the effects of energy expenditure in creating a negative energy balance and a resultant loss in body mass.
Can Weight Training or Resistance Exercise Significantly Contribute to the Creation of a Negative Energy Balance?
In comparison to aerobic exercise such as jogging or cycling, resistance exercise appears to have less of an impact on direct caloric expenditure and on creating a negative energy balance (Table 1) . For example, vigorous resistance exercise might burn only 66% of the calories of vigorous aerobic exercise during the same amount of exercise time. However, rest times between resistance exercises as normally performed during weight training were not accounted for in this example; thus, the amount of calories expended during an hour of resistance exercise was likely overestimated.
Despite the relatively low caloric cost of resistance exercise, this mode of exercise may significantly affect energy expenditure, but more through indirect than through direct means. The indirect effects of resistance exercise on energy expenditure are mainly through increasing
resting metabolic rate (RMR). Resistance exercise also enhances fat loss specifically through enhanced postexercise fat utilization, which will aid in weight loss and improved body composition.
Increased RMR
RMR is the amount of energy expended by the body at rest and accounts for about 70% of daily energy expenditure (1). An increase in RMR can have a significant impact on total energy expenditure and the creation of a negative energy balance. This increase in RMR is especially important when taking into consideration that RMR is generally depressed during caloric restriction, as when individuals are dieting (13).
Resistance training may significantly increase RMR by (a) increasing fat-free mass (FFM), (b) increasing plasma catecholamine levels, and (c) through acute or postexercise effects.
Increasing FFM
RMR is highly correlated with FFM, which is body mass accounted for by muscle, bone, and organ tissue. Because muscle mass is the only component of FFM than can be significantly altered, the 2 terms will be used synonymously. Muscle mass alone contributes about 22% to RMR (3). Consequently, any gain or loss of FFM may potentially alter an individual's RMR.
A number of researchers have looked at the effects of resistance exercise on FFM and subsequently on RMR. For example, in 1992, Ballor and Poehlman (2), using a cross-sectional design, assessed the effects of resistance exercise on RMR against a sedentary control. The resistance-trained group had an average of 2.6 kg more FFM and 7% higher RMR than did the sedentary control group. In 1994, Campbell et al. (5) examined the effects of a 12-week resistance training program on energy expenditure in 12 previously untrained men and women. At the end of the 12 weeks, the FFM increased by 1.4 kg and RMR increased 6.8%. When the increase in RMR was expressed relative to FFM, the change in RMR was no longer significant, suggesting that RMR increased in these participants based on their muscle or FFM gain.
In addition to increasing RMR through FFM, resistance exercise can help maintain muscle mass and RMR during diet-induced weight loss. During a very low calorie diet (VLCD), significant weight loss occurs. Without exercise, body fat is lost but muscle mass is also significantly wasted. The result of a significant loss of FFM due to dieting is a reduction in RMR.
Participating in resistance exercise during a VLCD maintains and may even increase FFM. A number of studies support this claim (4, 6). Recently, Bryner et al. (4) examined the effects on FFM and RMR of an 800-calorie diet (VLCD) plus resistance training or aerobic training. Twenty participants were randomized into aerobic exercise plus VLCD or resistance exercise plus VLCD so that the group was evenly distributed between both protocols. The aerobic exercise group lost a significant amount of FFM, but the resistance exercise group maintained FFM throughout the 12 weeks of training. Consequently, RMR decreased in the aerobic exercise group but increased in the resistance exercise group.
In 1993, Donnelly et al. (6) conducted a study to examine whether muscle hypertrophy or increases in muscle size could occur during severe caloric restriction (803.1 kcal/d) with resistance exercise. Fourteen obese females were recruited for the study and were randomized to either a diet only (C) or a diet plus weight training (WT) group. Women in both groups lost a significant amount of weight; however, the WT group demonstrated significant muscular hypertrophy after the 12 weeks of training, but there was no change in the C group. This study suggests that even during severe caloric restriction muscular hypertrophy is not altered during a resistance exercise program. Maintenance of or an increase in FFM will result in maintenance or an increase in RMR.
In light of the studies reviewed, resistance exercise may maintain and perhaps increase RMR in dieting and nondieting individuals through an increase or maintenance of FFM.
Increasing Plasma Catecholamine Levels
Endurance training increases plasma norepinephrine levels (10). The increase in norepinephrine results in an increased carbohydrate (CHO) and lipid metabolism or breakdown and thus an increase in RMR. If the same is true for resistance training, an increase in norepinephrine levels should increase RMR. In one study, the effects of resistance exercise on norepinephrine levels in the blood were examined.
In 1994, Prately et al. (11) performed a study that looked at the effect of resistance training on RMR and norepinephrine levels in older men. Thirteen older men (58 years old) participated in a 16-week heavy strength-training program. RMR and plasma norepinephrine levels were measured before the program started and after completion. RMR increased significantly (7.7%) as did plasma norepinephrine levels (36%). The results of this study suggest that resistance training increases plasma catecholamine levels, resulting in a contribution to increased RMR. The exact contribution of catecholamine levels to RMR was not determined in this study and is still unclear.
Postexercise Effects on RMR
During recovery from exercise, metabolic rate is maintained above resting values, a phenomenon referred to as excess postexercise oxygen consumption (EPOC). EPOC may significantly contribute to energy expenditure. However, it has been suggested that for EPOC to significantly contribute to energy expenditure after resistance exercise the training must be strenuous (requiring a high volume with a large number of sets and moderate resistance or intensity) (11). The results of several studies support this hypothesis (7, 9).
In 1993, Melby et al. (7) conducted a study to examine the acute effects of resistance training on postexercise energy expenditure and RMR. Seven male participants completed 90 minutes of resistance exercise; RMR was then measured for 2 hours postexercise and again the next morning (15 hours postexercise). RMR remained elevated for the 2 hours postexercise and after 15 hours RMR continued to remain elevated (+9.4%). Similar results were recently found in female participants following a similar program (9). RMR remained elevated for 3-hours postexercise and remained elevated the morning after exercise (+4.2%).
These studies demonstrate the potential for resistance exercise to contribute to energy expenditure. However, because the resistance exercise sessions performed in the previous studies were strenuous (high volume), nonathletes may struggle with or be unable to complete such a routine. When developing a resistance training protocol for untrained individuals with weight loss as a primary goal, strength and conditioning professionals should start the participant at a lower intensity and gradually progress the individual to an intensity appropriate for eliciting maximal increases in RMR.
The contribution of resistance exercise to RMR through increased FFM, elevated catecholamine levels, and EPOC has been established. Through increasing RMR, resistance exercise may contribute to increased daily energy expenditure, net negative energy balance, and therefore increased weight loss.
Increased Fat Oxidation
Fat oxidation, in the simplest terms, is the breaking down of fat for energy. Resistance exercise can cause an increase in fat oxidation both acutely and chronically (7, 11). The mechanism by which fat oxidation acutely increases is thought to be the increased use of CHO to replenish glycogen stores in the muscles (7). Glycogen is the stored form of glucose that supplies the muscles with energy during exercise. Because CHO is being stored at a greater rate after exercise than before exercise, the body must utilize fat as a primary source for energy. Increases in fat oxidation may also be attributed to an increase in catecholamines, which results in an increased rate of lipolysis or fat oxidation (11).
A few researchers have looked at this relationship between resistance exercise and fat oxidation. Recently, Osterberg and Melby (9) measured the effects of resistance exercise on RMR and fat oxidation. These authors discovered a 62% increase in fat oxidation 16 hours postexercise. Trueth et al. (12) found similar results in elderly women (12). After 16 weeks of resistance training, resting fat oxidation had increased by 63% and 24-hour fat oxidation had increased by 93%. The resistance training program used by Trueth et al. was fairly moderate, with a lower volume than that of Osterberg and Melby. There may be differences in the effects of resistance exercise on fat oxidation in elderly compared with young individuals. If such differences exist, strength and conditioning professionals should take age into consideration when prescribing a resistance exercise routine for fat or weight loss. Nonetheless, the results for both studies suggest that resistance exercise may play an important role in increasing fat oxidation and, consequently, increasing body fat loss.
Summary
The benefits of regular exercise for weight loss have been established for many years. Traditionally, aerobic exercise has been prescribed because of its ability to directly affect energy balance. Often when calorie restriction is used, body fat is lost but muscle mass is also lost, depending on the severity of the caloric restriction. The loss of muscle mass may result in a decrease in RMR, which is contraindicated for weight loss or maintenance of weight after weight loss. Hence, maintaining muscle mass during and after weight loss is an important component to any weight loss program.
Resistance exercise has an indirect impact on weight and fat loss through increasing RMR and enhancing fat oxidation. Increasing or maintaining muscle mass or FFM, increasing serum catecholamine levels, and enhancing postexercise utilization of energy are all factors that play a role in the ability of resistance exercise to increase RMR. Because resistance exercise maintains or increases muscle mass, even during severe caloric restriction, RMR will remain elevated or will be maintained during weight loss. In addition to increased RMR, the rate of fat oxidation is affected both acutely and chronically.
Practical Application: What Should Strength and Conditioning Professionals Recommend to Those Who Seek Weight Loss as a Desired Goal (Referring to Exercise)?
Strength and conditioning professionals should prescribe a combination of aerobic exercise and resistance exercise for directly burning calories and for indirectly burning calories and maintaining lean body mass, respectively. For the untrained person, a resistance training program should be low volume and low intensity (1 set, 10–12 repetitions maximum [RM]) and should gradually build to a routine with higher volume and moderate intensity (3 or 4 sets, 8–12 RM) to elicit increases in RMR (Table 2) . For a trained individual, simply increase the number of sets, increase the intensity, and adjust the number of repetitions accordingly. The exercises are ordered in an alternating upper-body and lower-body manner to ensure adequate recovery between exercises (8). Through the use of aerobic and resistance exercise, optimal body weight and physical fitness may be obtained. For fitness professionals, the importance of aerobic and resistance exercise is clear: to achieve optimal health and body weight, we need both.
References
1. American College of Sports Medicine. ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription (4th ed.) Baltimore: Williams & Wilkins, 2001.
2. Ballor, D.L., and E.T. Poehlman. Resting metabolic rate and coronary-heart-disease risk factors in aerobically and resistance-trained women. Am. J. Clin. Nutr. 56:968–974. 1992. [PubMed Citation]
3. Bray, G.A., C. Bouchard, and W.P.T. James. Handbook of Obesity. New York: Marcel Dekker, 1998.
4. Bryner, R.W., I.H. Ullrich, J. Sauers, D. Donley, G. Hornsby, M. Kolar, and R. Yeater. Effects of resistance vs. aerobic training combined with an 800 calorie liquid diet on lean body mass and resting metabolic rate. J. Am. Coll. Nutr. 18:115–121. 1999. [PubMed Citation]
5. Campbell, W.W., M.C. Crim, V.R. Young, and W.J. Evans. Increased energy requirements and changes in body composition with resistance training in older adults. Am. J. Clin. Nutr. 60:167–175. 1994. [PubMed Citation]
6. Donnelly, J.E., T. Sharp, J. Houmard, M.G. Carlson, J.O. Hill, J.E. Whately, and R.G. Israel. Muscle hypertrophy with large-scale weight loss and resistance training. Am. J. Clin. Nutr. 58:561–565. 1993. [PubMed Citation]
7. Melby, C., C. Scholl, G. Edwards, and R. Bullough. Effect of acute resistance exercise on postexercise energy expenditure and resting metabolic rate. J. Appl. Physiol. 75:1847–1853. 1993. [PubMed Citation]
8. National Strength and Conditioning Association. Essentials of Strength Training and Conditioning (2nd ed.) Champaign, IL: Human Kinetics, 2000.
9. Osterberg, K., and C. Melby. Effect of acute resistance exercise on postexercise oxygen consumption and resting metabolic rate in young women. Int. J. Sports Nutr. Exerc. Metab. 10:71–81. 2000.
10. Poehlman, E.T., and E. Danforth. Endurance training increases metabolic rate and norepinephrine appearance rate in older individuals. Am. J. Physiol. 261: (Endocrinology Metabolism 24). 233–239. E. 1991.
11. Prately, R., B. Nicklas, M. Rubin, J. Miller, A. Smith, M. Smith, B. Hurley, and A. Goldberg. Strength training increases resting metabolic rate and norepinephrine levels in healthy 50- to 65-yr old men. J. Appl. Physiol. 76:133–137. 1994. [PubMed Citation]
12. Trueth, M.S., G.R. Hunter, R.L. Weinsier, and S.H. Kell. Energy expenditure and substrate utilization in older women after strength training: 24-h calorimeter results. J. Appl. Physiol. 78:2140–2146. 1995. [PubMed Citation]
13. Wadden, T.A., G.D. Foster, K.A. Letizia, and J.L. Mullen. Long-term effects of dieting on resting metabolic rate in obese outpatients. J. Am. Med. Assoc. 264:707–711. 1990. [PubMed Citation]
Jeffrey L. Alexander, MS, ACSM-ES, is a doctoral student in Exercise and Wellness at Arizona State University–East. He obtained a BS in Health Promotion and an MS in Exercise Physiology and is an adjunct faculty member at the Chandler-Gilbert Community Colleges, Williams and Pecos Campus. His research focus is on strength training as a prevention and treatment for
cardiovascular disease and related chronic diseases.
