|Aerobics vs. Resistance Training
Is This the Battle of the Fitness Titans?
Len Kravitz, Ph.D.
For years the virtues and values of aerobic exercise have been extolled and celebrated while the benefits of resistance training have been minimized to that of building muscles and improving sports performance. More recently, the traditional perception of resistance training has undergone a revitalization due to scientific evidence suggesting powerful health status betterment. In fact, for those of you spending many a moment on the Internet, there are a lot of voices out there in the World Wide Web now chanting that resistance training is the superior and only form of exercise you need. How the pendulum has changed! The good news is that the evidence supports remarkable claims for aerobics and resistance training for improvement in health. This battle of the fitness titans is attributable, unfortunately, to a blaring cluster of uninformed individuals. Therefore, the purpose of this article is to provide scientific evidence how resistance training and aerobic exercise are key constituents of health, fitness and longevity (summarized in Table 1), and bring to realization that including both of them in our physical activity programs allows our students and clients to be the biggest winners.
Bone Mineral Density
Physical activities that stimulate bone growth need to include progressive overload, variation of load, and specificity of loading (Conroy, Kraemer, Maresh, & Dalsky, 1992) . Specificity of loading refers to exercises that directly place a load on a certain region of the skeleton. With osteoporosis, a degenerative disease characterized by a loss of bone mineral density resulting in a susceptibility to bone fractures and health problems, it appears resistance training and aerobic exercise may provide the needed stimulus for bone formation (Rubin & Lanyon, 1984) . Progressive overload is necessary so the bone and associated connective tissue do not exceed the critical level that would place them at risk. In an eight-month study of premenopausal women doing resistance exercise or jogging, bone mineral density improved in both groups with no difference between groups (Snow-Harter, Going, & Pamenter, 1995) . It appears that increases of bone mineral density are site-specific. Hamdy et al (1994) reported greater increases in bone tissue in the upper arm of resistance trained subjects as compared to runners, although both groups showed similar changes in the lower body. Exercise programs to increase bone growth should be full-body in nature, including exercises such as squats and lunges which direct the forces through the axial skeleton and allow greater loads to be utilized (Conroy & Earle, 1994) . In addition, evidence does suggest that moderate weight-bearing activity, such as brisk walking done regularly, and for a long-term basis, is effective in averting age-related bone loss (Vuori, 1995)
Hypertension is a major health problem. Elevated systolic and diastolic blood pressure is associated with a higher risk of developing coronary artery disease (CAD), congestive heart failure, stroke, and kidney failure. There is a onefold increase in developing these diseases when blood pressure is 140/90 mmHg (Bouchard & Despres, 1995) . It is necessary for the fitness professional to also educate clients that reducing weight and lowering alcohol and salt intake may help reduce elevated blood pressure in many cases. Intervention studies have shown that regular aerobic activity can reduce systolic and diastolic blood pressure by approximately 10 mmHg (Hagberg, 1990) . Also, moderate-intensity exercise (40%-70% of VO2max) tends to produce greater decreases in resting blood pressure than higher intensity exercise. Although regular aerobic exercise will not likely affect normotensive individuals, habitual aerobic exercise may be protective against the increase in blood pressure commonly seen with increasing age (Blair, Goodyear, Gibbons, & Cooper, 1984) .
During resistance exercise, systolic and diastolic blood pressures may show steep increases, which indicates that caution should be observed with persons with known cardiovascular disease or risk factors (Stone, Fleck, Triplett, & Kramer, 1991) . These increases in blood pressure are dependent on the intensity of the contraction, the length of time the contraction is held, and the amount of muscle mass involved in the contraction (Fleck, 1988) . More dynamic forms of resistance training, such as circuit training, that involve moderate resistance and high repetitions with short rests are associated with reductions in blood pressure. Studies have shown decreases in diastolic blood pressure (Harris & Holly, 1987) , no change in blood pressure (Blumenthal, Siegel, & Appelbaum, 1991) , and decreases in systolic blood pressure (Hagberg et al., 1984; Hurley, Hagberg, & Goldberg, 1988) . More research is necessary to clearly understand the role of resistance training in blood pressure management.
Resting Heart Rate
In terms of chronic adaptations, there appears to be a reduction in heart rate from resistance training, which is considered favorable (Stone et al., 1991) . Long term adaptations observed in the research show from no change up to a 11% decrease in heart rate, which may be explained by the differences in intensity, volume, rest between sets, use of small vs. large muscle mass, duration of study and fitness level of the subjects.
Regular participation in aerobic exercise often results in a decrease in resting heart rate by 5 to 25 beats per minute. The lowered resting heart rate from exercise training is proposed to be due primarily to an increase in the parasympathetic nervous activity with a minor decrease in sympathetic nervous discharge (Katona, McLean, Dighton, & Guz, 1982; Smith, Hudson, Graitzer, & Raven, 1989) .
Blood Lipids and Lipoproteins
It is well-established that low plasma triglycerides, total cholesterol, and low-density lipoprotein cholesterol (LDL-C) levels, as well as elevated high-density lipoprotein cholesterol (HDL-C) levels, are associated with a lowered CAD risk. Regular aerobic exercise has been shown to lower blood triglycerides in individuals with initially high levels, with no influence on persons with normal concentrations. All intensity (low, medium, high) levels of aerobic exercise have shown increases in HDL-C, particularly the HDL2 subfraction, as well as favorably altering total cholesterol and LDL-C (Bouchard & Despres, 1995) . The commonality seen in endurance exercise programs that positively affects blood lipid profiles is that the training creates a substantial negative energy balance (Despres & Lamarche, 1994) .
Although several studies have shown favorable impact of resistance training on blood lipids, several others have reported no change. It has been suggested that the resistance programs that best modify blood lipid profiles incorporate larger muscle mass, multi-segment exercises with a high total volume (reps x sets x load) prescription (Stone et al., 1991) . Additional research needs to be conducted which controls for body composition changes, day-to-day variations in lipoproteins, dietary factors, and possible other training adaptations to provide a more credible summary of the effect of resistance training on blood lipids and lipoproteins.
Elevated insulin and blood glucose levels are characteristic features involved in the development of non-insulin-dependent diabetes mellitus, which develops primarily in adult women and men who are overweight and have excess abdominal fat tissue. One of the benefits of aerobic exercise is the improvement of the sensitivity of liver, skeletal muscle and adipose tissues to insulin action. A decrease in blood plasma glucose in hyperglycemic individuals is also see with chronic aerobic activity. There is very persuasive evidence, from three large studies, that regular aerobic activity actually plays a substantial role in maintaining normoglycemia and insulin sensitivity in nondiabetic individuals (Bouchard & Despres, 1995) .
Improvements in glucose metabolism with strength training, independent of alterations in aerobic capacity or percent body fat, have also been shown (Hurley et al., 1988; Smutok, Reece, & Kokkinos, 1993) . Smutok et al. (1993) concluded that strength training and aerobic training improved glucose tolerance and reduced insulin responses to oral glucose (in men) similarly. It appears that both resistance training and aerobic exercise offer a strong protective role in the prevention of non-insulin-dependent diabetes mellitus.
Numerous controlled training studies have tested for the effects of intensity, duration and frequency of aerobic exercise on maximal oxygen uptake (VO2max). A minimum of 20 minutes of aerobic exercise at 50% or more of the individuals VO2max, on three or more days per week, will produce a 10% to 20% increase in VO2max in most sedentary persons (ACSM, 1995) . The literature thoroughly supports the evidence that exercise intensity is directly related to the change in VO2max (Gossard et al., 1986) . Higher doses of aerobic exercise produces greater increases in VO2max, although these improvements are not proportionately greater.
Traditional resistance training that employs sets followed by 1 to 2 minutes of rest has not shown an increase in VO2max. Studies have shown little to mild improvement in aerobic capacity (5% to 9.5%) from participation in circuit weight training (Kass & Castriotta, 1994; Peterson, Miller, Quinney, & Wenger, 1988) . Kass and Castriotta suggest that the mild increases in aerobic capacity are due primarily to increases in fat-free mass from the circuit weight training, and not changes from the main factors affecting aerobic capacity: cardiac output (heart rate x stroke volume) or arterial-venous oxygen difference (exchange of oxygen and carbon dioxide at the cellular level).
A negative energy balance generated by cardiorespiratory activity, instead of reduced caloric intake, and sustained for several months has been shown to result in weight loss that is predominantly attributable to a loss of body fat (Bouchard & Despres, 1995) . In contrast, when the negative energy balance is caused by lower energy intake (through diet alone), one also loses a significant amount of lean tissues, which may be as much as 50% of the total weight loss (Tremblay, Despres, & Bouchard, 1985) .
Resistance training and circuit training studies have shown decreases in body weight and fat mass with comparable increases in fat-free mass (Gettman & Pollock, 1981) . One of the noteworthy benefits of resistance exercise, as it relates to weight loss, is the positive impact of increasing energy expenditure during the exercise session and on maintaining, or increasing, fat-free body mass while encouraging the loss of fat body weight (Young & Steinhard, 1995) . An impressive finding to highlight with resistance training is that the energy expenditure following higher total volume workouts appears to be elevated, with an increase in fat utilization (due to a lower respiratory exchange ratio) during this period (Melby, Scholl, Edwards, & Bullough, 1993) . The evidence unequivocally supports the combined use of aerobic exercise and resistance training for optimal changes in body composition to successfully attain weight management goals.
Resting Metabolic Rate
The largest single source of energy expenditure is the resting metabolic rate, which is defined as the energy necessary to maintain the bodys physiological systems at rest. It is accountable for 60% to 75% of the daily energy expenditure and closely associated to the fat-free body mass. Some researchers have shown that resting metabolic rate may be influenced by aerobic exercise training while others have failed to show a difference. Tremblay et al (1985) measured resting metabolic rate in untrained, moderately trained (6-10 hrs of vigorous exercise weekly) and highly trained (12-16 hours of vigorous) young males. Results showed that the relative resting metabolic rate was significantly increased in the highly trained subjects, while no difference was seen between the moderately trained and untrained subjects. It has been suggested that this increased resting metabolic rate, observed in high-intensity aerobic endurance training, may be a result of an increased energy intake and expenditure (high caloric turnover) and other accumulative factors due to intensity, duration and frequency affecting post-exercise energy expenditure (Van Zant, 1992) .
Several studies, with adult men and women of various ages, have demonstrated significant increases in lean body mass which has been shown to increase resting metabolic rate (Pratley et al., 1994). The key factor seen in the training programs appears to be the total volume of training using the major muscle masses of the body (Stone et al., 1991).
Muscle mass, strength, power and endurance are all important for the prevention of several diseases, injuries and the improvement of movement capabilities. Although these components of musculoskeletal health show substantial decreases with age, it has been suggested that this is due largely to a decrease in physical activity, and not solely age (Bassey & Harries, 1993) . This decrease in strength is linked to decreased mobility and increased risk of falling, which has been identified as the most frequent cause of injury related to mortality (Pollock, Vincent, Corbin, & Pangrazi, 1996) . Substantial improvement in all of the components of musculoskeletal health, as a result of resistance training, have been shown in sedentary, disabled, young, physically active, and very old frail individuals (Vuori, 1995) .
Functional capabilities can be defined as the ability to perform basic physical actions such as walking, climbing stairs, reaching, stooping, bending and grasping, which are fundamental components of daily living. Experimental and observational research show that aerobic exercise and resistance training contribute to the maintenance of functional capabilities during aging (Buchner, Beresford, Larson, LaCroix, & Wagner, 1992; Wagner & Lacroix, 1992) . Also, comprehensive programs for the improvement of low back health include aerobic exercise and muscular fitness exercises (Plowman, 1992) .
Estimates of the extension of life comparing men who expended&Mac179;2,000 kilocalories per week in physical activity, including walking, recreational activities and stair climbing, to men who expended <500 kilocalories per week in similar activities, for over 16 years, found the active men to live upwards of two years longer (Paffenbarger & Lee, 1996) . This difference held after controlling for cigarette smoking, body weight, hypertension, and age. Similarly, with regular walking, cycling and cross-country skiing as the activity variables of interest (and then standarizing for age, systolic blood pressure, cholesterol, and body mass), researchers in Eastern Finland showed that active men live an extra 2.1 years when compared to their inactive counterparts, during a 20-year study (Paffenbarger & Lee, 1996) . Indeed, a convincing relationship exists between moderate-intensity physical activity and longevity.
Directions for the Future
Numerous health and fitness benefits have been documented for both resistance training and aerobic exercise. If health and fitness professionals prescribe to the new expanding model of physical activity for the enhancement of health, it is clear that program prescriptions need to include resistance training and aerobic exercise. With the merging of the computer and communication technologies, broad access to the Internet and World Wide Web will be more available and affordable. This presents new opportunities and challenges for health professionals. More education and information about health, fitness and longevity will be easier to disseminate to an interested, growing audience. However, one impact is clear, with more time spent on a computer, people may find it harder to find time for physical activity. Instead of debating the pros and cons of aerobic vs. resistance training, perhaps we as a profession should focus now on how to best design optimal workout programs for the demands of the next century.
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