Resistance Training and Weight Management
The caloric expenditure both during and after resistance exercise can help your members to achieve their weight-management goals.
Scientific and anecdotal evidence increasingly suggests that regular resistance exercise (RE), when appropriately prescribed, favorably changes muscular strength, endurance and power; bone mineral content; body composition; cardiovascular function; metabolism; and psychological well-being. Furthermore, while this form of exercise has traditionally been viewed as a means to increase muscular mass, strength and power, its beneficial relationship to health factors and chronic disease continues to be recognized. As such, organizations including the American College of Sports Medicine, American Heart Association, and the American Association of Cardiovascular and Pulmonary Rehabilitation have included RE in their current recommendations.
Empirical observations indicate that more individuals are becoming regularly involved in this activity. Together with the metabolic adaptations resulting from the performance of regular structured RE, recent findings suggest that this form of physical work may prove beneficial as a principal component in a weight-management regimen. Following are some of the key areas in which a program of RE may aid in the maintenance of body weight as part of a complete health and fitness routine.
Energy expenditure during exercise
While it appears true that cardiovascular exercise (CV) such as walking/jogging, stair-stepping and cycling leads to greater overall energy expenditure than does RE, individuals should not discount the role of RE in this regard. Often trainers prescribe CV exercise for purposes of caloric expenditure and weight management, and RE for purposes of muscular development. This general idea that CV exercise leads to greater caloric expenditure comes from studies that have actually measured the energy cost of these two distinct forms of exercise. Most studies have reported close to three times the energy cost for CV exercise compared to RE. That is, for the typical 30-minute workout, CV exercise may lead to an energy expenditure of 300 to 400 calories, while RE may burn roughly 150 calories for most individuals. Of course, the total caloric cost depends on the specific protocol used, including the mode, intensity and rest interval length. This is especially important with regards to RE, as many studies have used circuit training programs involving a mix of larger and smaller muscle groups in their design, and compared the energy cost to large-muscle-group CV exercise such as treadmill running. However, when appropriately matching the muscle mass trained and the relative exercise intensity, the caloric cost of CV and RE sessions may be more similar.
We recently tested this hypothesis in our lab by having subjects perform both 30 minutes of continuous cycling at 70 percent of VO 2 max, and intermittent free weight squatting (using 120-second rest intervals between sets) at 70 percent of a one repetition max (1-RM), separated by one to two weeks. Cycling resulted in greater total calorie expenditure than did squatting (approximately 430 vs. 270 calories). However, when considering the total amount of time spent exercising (30 minutes for cycling vs. approximately six minutes for squatting), the amount of work performed per minute during squatting was greater than during cycling, which corresponded to a greater energy-cost-per-minute of exercise. These results suggest that RE, as performed in this study, is associated with a per-minute energy cost that exceeds that observed with continuous CV exercise. Such findings may have further implications for the inclusion of RE as a principal component in weight-management programs.
Energy expenditure post exercise
Following an acute bout of RE, the body continues to use oxygen at a greater rate than prior to exercise. This is referred to as excess post-exercise oxygen consumption (EPOC), and may be due to the body's need to return all systems to normal resting levels (homeostasis). This may involve a resynthesis of energy sources (creatine phosphate and ATP), the removal and usage of lactate (a metabolic byproduct of RE), a resynthesis of glycogen (a storage form of carbohydrate primarily in skeletal muscle and the liver), and a normalization of breathing, heart rate, body temperature, and circulating catecholamine (epinephrine and norepinephrine) and anabolic hormones.
The extent and duration of EPOC appears to vary, dependent mainly on the training status of the individual, and the intensity and type of exercise performed. Well-conditioned individuals may not experience as great of an increase in energy expenditure post exercise, as they generally recover quicker than do those who are relatively untrained. Also, exercise performed at higher intensities, in addition to exercise that may involve muscle damage that necessitates healing (such as RE), results in greater EPOC than does lower-intensity or aerobic exercise. In fact, some studies have demonstrated an increase in resting metabolic rate (RMR) up through 24 hours following a bout of RE. This is likely due to the increased energy requirement for repairing damaged muscle tissue as a result of unaccustomed exercise.
Therefore, RE does not only lead to energy expenditure during the exercise session, it also may lead to increased energy expenditure during the hours following an exercise bout. However, when considering that 1 pound of fat contains roughly 3,500 calories, the rise in total caloric expenditure of a few hundred calories above what would normally be needed during the hours following a bout of RE may seem negligible. What needs to be considered is the total additional energy expenditure over time (i.e., months and years), which may significantly help with weight-management goals.
Energy expenditure at rest
While attempts to manage body weight have traditionally focused on dietary intake and exercise (typically cardiovascular), resting energy expenditure also needs to be considered. RMR, which is the rate at which calories are burned while at rest in order to fuel various physiological systems, appears to account for the majority of daily energy expenditure (roughly 60 to 70 percent). Several factors account for RMR, including age, gender, genetic factors and body composition. While some of these factors cannot be controlled, body composition seems to be regulated to a great deal by both nutritional intake and exercise, in particular RE. This is because RE often leads to an increase in the amount of fat-free mass (muscle and bone), in addition to a decrease in fat mass. Because muscle is more "energy costly" to maintain than fat mass, any increase in muscle mass should, theoretically, produce an increase in RMR, allowing for better body-weight control. Likewise, a decrease in RMR, as often seen with aging (likely due to the loss of fat-free mass), can decrease energy expenditure at rest, making it more difficult to maintain body weight.
These findings have been presented in the scientific literature, as well as reported by individuals involved in RE programs. Therefore, it appears that a RE program targeted toward increased muscle mass may be a consideration if the goal is to better maintain body weight.
Aside from the role of RE to stimulate an increase in exercise and post-exercise/resting energy expenditure, it should also be noted that RE has the ability to alter the processing of nutrients consumed through dietary sources. In particular, as with CV exercise, RE has a profound effect on blood glucose regulation and insulin secretion. An acute bout of exercise enhances the uptake of glucose from the bloodstream into skeletal muscle where it can be stored as glycogen. Under normal resting circumstances, an increase in blood glucose following eating will lead to a rise in circulating insulin. The action of insulin here is to clear glucose from the bloodstream and to allow for uptake into tissues. An acute bout of exercise can produce a similar change in blood glucose levels, although it appears that exercise can mediate these changes via an insulin-independent mechanism. In particular, exercise can increase certain transport proteins that facilitate glucose uptake from the bloodstream into tissues (i.e., skeletal muscle). In this way, exercise imparts an insulin-like effect, and less insulin is needed to handle blood glucose homeostasis.
This seems important, as insulin itself, while of utmost importance within the body, acts to store nutrients (potentially as body fat) and inhibits the use of fat as a fuel source during exercise if circulating levels are high. Therefore, controlling insulin levels through both dietary intake and regular exercise (including RE) may have important long-term implications pertaining to weight management. Furthermore, as discussed above, because RE has the ability to increase the degree of muscle mass, the additional muscle mass gained should allow for better control of blood glucose, as more tissue is available for the uptake of glucose from the bloodstream.
Types of RE programs
While numerous programs exist that canleadclients to their desired goals, the RE program most often prescribed for weight management is that consisting of one to two sets of 12 to 15 reps for all major muscle groups. The idea is that individuals looking to maintain/lose weight certainly do not want to use heavy weights/higher intensities, in fear that they will develop too much muscle mass. (Of course, those who have actually trained for this purpose realize that it is certainly not that easy!) Therefore, offer clients a balanced, well-thought-out RE program that includes periods of lower-intensity (lighter weight), higher-rep, shorter-rest interval training, interspersed with moderate- and higher-intensity (heavier weight) training involving a lower number of reps and longer rest intervals. Major muscle groups such as the legs, back, chest, deltoids, abs and low back -- in addition to compound exercises such as squats, deadlifts, pulldowns, bench presses and military presses -- should be the primary focus, as these are responsible for yielding the greatest increase in energy expenditure. The total volume (sets, reps, tempo), intensity and frequency of the program should be altered frequently, and be based on the client's conditioning level and recovery ability. Of course, the individual's level of conditioning needs to be considered prior to starting such programs.
An additional consideration is the inclusion of both a cardiovascular and resistance component mixed within the same session. This may include choosing four to five major exercises, as suggested above, which are performed back to back with little-to-no rest in between sets. Then, as an "active rest" period, exercisers can perform three to five minutes of CV exercise at a moderate pace. Following this, they can repeat the sequence for a total of five to six sets. A fairly well-conditioned individual will be exhausted at the end of such a session. However, the benefits are numerous. Most importantly, the workout is challenging and enjoyable.
While short-rest interval training may require more energy to perform, the higher-intensity, longer-rest interval work may be associated with a greater energy cost following exercise, in addition to an increase in muscle mass, which should favorably affect RMR. Therefore, such periods of higher-intensity work should not be eliminated from a RE program aimed at weight management. Ideally, these programs will be changed once every four to six weeks, so as to avoid boredom and reaching a stalemate, understanding that any RE program is only as good as the time it takes for a client to adapt. (For more detailed information regarding the design of RE programs, refer to the reference section.)
Exercise programs involving structured RE are associated with numerous benefits, including aiding in weight management. From the available scientific evidence, it appears that RE can result in a significant caloric expenditure during exercise, following exercise and at rest, due to an increase in muscle mass. Furthermore, metabolic adaptations specific to blood glucose and insulin regulation may assist with minimizing excess body fat accumulation and enhancing fat usage. Together, these changes should aid in the maintenance of a desired body weight, in conjunction with a program of aerobic exercise and healthful eating. FM
By Richard J. Bloomer, Ph.D., C.S.C.S.