One advantage of the circuit strength training program was the shorter workout duration (25 minutes/session), with 1-minute exercise segments. Another advantage was the less frequent training schedule that matched the updated recommendations from the American College of Sports Medicine (ACSM) and the American Heart Association for vigorous-intensity aerobic activity performed a minimum of 20 minutes on 3 days each week (20). In addition, the circuit strength training exercises involved easily adjusted external resistance rather than fixed body weight resistance. However, the most notable difference between the traditional and the alternative training program was the latter's emphasis on resistance exercise. It would seem that a relatively brief strength training circuit is an effective means of improving body composition and enhancing key components of physical fitness in poorly conditioned Air Force personnel (50). Other circuit strength training programs have produced significant improvements in body composition, muscular strength, and cardiovascular endurance in healthy adults (15,16), college students (33), hypertensive adults (19), and cardiac patients (25).
FACTORS IN FAT GAIN
On average, adults who do not strength train lose approximately 4 to 6 lbs of muscle tissue per decade throughout the aging process (11,12,13). This often unnoticed loss of muscle may be the single largest contributor to the decline in resting metabolic rate (40) that averages 2% to 3% per decade in adults (26). The breakdown and synthesis of muscle protein are largely responsible for the energy expenditure associated with resting muscle tissue, which approximates 5 calories per day for each pound of muscle (53). Because resting metabolism accounts for about 70% of daily calorie use among sedentary adults, reduction of muscle mass and resting metabolic rate may be accompanied by an increase in fat weight (53). Assuming a consistent dietary pattern, the calories that were previously used to maintain the lost muscle tissue are stored as fat.
For example, a 2% per decade drop in resting metabolic rate actually averages a 1% reduction in resting calorie use over that 10-year period. Assuming a resting metabolism of 1,500 calories per day, this would average 15 fewer calories burned at rest on a daily basis. Although seemingly insignificant, if other things remain the same, a 15-calorie per day resting metabolic rate deficit may lead to a 15-lb per decade fat gain (15 calories × 365 days × 10 years = 54,750 calories ÷ 3,500 calories/lb fat = 15.6 lbs fat). Although eating more food or doing less physical activity can clearly contribute to fat accumulation, in a society characterized by volitional dietary restriction and chronic physical inactivity, it is likely that muscle loss and metabolic slowdown are factors in progressive fat gain.
FACTORS IN FAT LOSS
If the above assumptions are correct, a logical approach to fat loss would be to reverse the factors that lead to fat gain. There is evidence that the insidious process of muscle atrophy, resting metabolic rate reduction, and fat accumulation may be reversed through regular resistance exercise. For example, our study with 1,644 previously inactive adults and older adults showed an average lean (muscle) weight gain of 3.1 lbs (assessed by skinfold calipers and ultrasound technology) after 10 weeks of circuit strength training (49). Although we did not measure resting metabolism, other strength training studies have reported similar lean weight gains accompanied by 7% to 8% increases in resting metabolic rate (9,22,41). A recent study by Hackney et al. reported an average 8% increase in resting energy expenditure for 3 days after a high-effort strength training session (18). Other researchers, however, have failed to find an association between strength training and resting metabolic rate elevation (8,14,46).
A possible explanation for these different research results may be the intensity of the strength training workouts. For example, the Hackney et al. study used a very intense training protocol (eight exercises for eight sets of six repetitions with an eccentric emphasis) that produced high levels of delayed-onset muscle soreness and would not be appropriate for beginning participants (18). On the other hand, low-volume training protocols performed to volitional fatigue have been associated with significant increases in resting metabolic rate (9,22,41). It should be noted that single-set strength training performed at high effort levels also can produce a degree of delayed-onset muscle soreness.
With respect to fat loss, the same studies that showed approximately 3 lbs of lean weight gain reported approximately 4 lbs of fat loss (9,22,41,49). These findings indicate that strength exercise may be effective for rebuilding muscle and reducing fat over training periods of 10 to 25 weeks.
HEALTH BENEFITS OF STRENGTH EXERCISE
In addition to decreasing body fat and reducing the risk of obesity (31), strength training stimulates a variety of positive adaptations that enhance both physical and mental health. Resistance exercise has produced beneficial outcomes for numerous physiological factors, including increased blood glucose utilization (34), reduced resting blood pressure (19), improved blood lipid profiles (6), enhanced vascular condition (38), increased gastrointestinal transit speed (27), increased bone mineral density (35), and improved body composition (10). It also has been shown to improve function in postcoronary patients (17) and chronic obstructive pulmonary disease (COPD) patients (21), as well as to reduce discomfort in people with low back pain (42) and arthritis (29). In addition, strength training has proved effective for decreasing depression (44) and for reducing the risk of metabolic syndrome (24,52), cardiovascular disease (7), and premature all-cause mortality (23).
The medical applications of strength training were further supported by a recent conditioning study with coronary disease patients (30). All of the subjects exercised 5 days per week for a period of 6 months. Those who alternated 3 days of endurance exercise with 2 days of strength training experienced approximately 50% more improvement in aerobic function (V˙O2 peak) than those who performed 5 days of endurance exercise only.
Why would 3 days of endurance exercise and 2 days of strength training produce more cardiovascular benefit than 5 days of endurance exercise alone. Consider that muscles function as the engines of the body, namely, the tissues where combustion takes place, energy is released, force is produced, and movement originates. As such, stronger muscles can have a positive impact on other body systems, including the skeletal system (32,35), cardiovascular system (7,30), gastrointestinal system (27), endocrine system (34), and neuromuscular system (42). A well-conditioned muscular system enables a physically active lifestyle and enhances numerous health factors that may reduce the risk of selected degenerative diseases and medical problems (53).
ACSM STRENGTH TRAINING GUIDELINES
In 1995, ACSM published research-based guidelines for a safe, effective, and time-efficient strength training protocol (1). These guidelines were essentially the same as the latest ACSM strength training recommendations (2006) that call for the following exercise procedures (2):
Beginning in 1996, we studied a total of 1,644 men and women aged between 21 and 80 years who completed essentially identical 10-week training programs using the ACSM minimum protocols for strength and endurance exercise (1). On average, the participants added 3.1 lbs of lean weight and lost 3.7 lbs of fat weight (49). They also reduced their resting systolic blood pressure by 3.8 mm Hg and their resting diastolic blood pressure by 1.8 mm Hg. The Table presents the results of the relatively brief workouts for subjects who did two or three exercise sessions per week for 10 weeks.
As shown in the Table, two and three weekly strength training sessions proved equally effective for increasing lean (muscle) weight. Apparently, when following the ACSM strength and endurance training guidelines, two exercise sessions per week provide the essential stimulus for muscular development. The 3.1-lb increase in lean weight was similar to the lean weight gains experienced by subjects in other studies who performed strength training only (9,22,35,41). This outcome indicates that a combined program of strength and endurance exercise using the ACSM minimum training protocols may be as effective as strength training alone for increasing lean weight in previously inactive adults.
When examined by sex, the mean lean weight gain was significantly greater for men (4.6 lbs) than for women (2.6 lbs) (49). When examined by age, there were no significant differences in lean weight gain. Participants aged 21 to 44 years, 45 to 54 years, 55 to 64 years, and 65 to 80 years added 2.5 lbs, 3.1 lbs, 2.9 lbs, and 3.2 lbs of lean weight, respectively. Although the rate of lean weight gain is likely to decline in longer training programs, a later study using the same ACSM exercise protocols showed consistent increases in lean weight during both halves of a 6-month training period. The 46 participants (almost all of whom were middle-aged women) added 2.2 lbs of lean weight during the first 3 months of training and 2.5 lbs of lean weight during the second 3 months of training (51).
These findings suggest that the minimum ACSM training protocols may be productive for beginning participants for at least the first several months of a regular exercise program. However, in a 2-year study by Schmitz et al., the strength training group members increased their lean weight by 4.3% during the first year, but had no further lean weight gain during the second year (43).
Unlike diet programs, which are typically short-term, strength training should become a permanent lifestyle activity. Unfortunately, diet programs reduce muscle mass and decrease resting metabolism (5), essentially promoting fat regain (28). Conversely, strength training rebuilds muscle tissue and increases resting metabolic rate, which are positive factors in attaining and maintaining fat loss. Whereas dieting characteristically reduces energy for physical function, strength training uses energy to increase physical function. Considering these advantages over dieting alone, it would seem reasonable to include strength exercise in weight loss programs. This information is consistent with the recently released ACSM Position Stand, "Appropriate Physical Activity Intervention Strategies for Weight Loss and Prevention of Weight Regain for Adults."
In addition to the favorable physiological adaptations associated with resistance exercise, the minimum ACSM strength and endurance training protocols may provide important psychological benefits. Separate studies using the same ACSM exercise program have revealed favorable changes in a variety of feelings and mood states. Using the Exercise-Induced Feeling Inventory to assess personal feelings before and after a single training session, we found significant improvements in the categories of positive engagement, revitalization, tranquility, and physical exhaustion (4). After exercise, the participants felt more purposefully engaged, more energetic, less troubled, and less fatigued.
Using the Tennessee Self-Concept Scale, Second Edition, and the Profile of Mood States to assess psychological changes during the 10-week training program, we found significant improvements in physical self-concept, total mood disturbance, depression, and fatigue (3). These positive changes contributed to the participants' improved attitude, self-confidence, and reinforcement with respect to physical activity.
Our 10-week studies using the ACSM strength and endurance training protocols have averaged a 91% completion rate, and our 6-month study had a 68% completion rate. In all of the studies, more than 95% of those who finished the exercise program rated the strength training component four or five on a 5-point scale (1 = lowest, 5 = highest) of personal satisfaction. During the 14 years (1995-2009) that we have used the ACSM training protocols for our exercise studies, only a few participants have reported exercise-related injuries (most were a recurrence of previous physical problems). It would therefore seem that the ACSM minimum training protocols for strength and endurance exercise provide a relatively safe and satisfying means for increasing lean weight and reducing fat weight in previously inactive adults.
Several studies suggest that strength training may be an effective means of rebuilding muscle, recharging metabolism, and reducing fat in previously inactive adults and older adults. Training programs using the minimum ACSM protocols for strength and endurance exercise have shown significant improvements in body composition and resting blood pressure after 10 weeks of training. In fact, combined strength and endurance training seems to provide the same muscular benefits as strength training alone. Although there are numerous other strength training protocols, the ACSM guidelines seem well suited for the large percentage of our adult population who need to add muscle and lose fat. Research indicates that strength training may play an important role in fitness and health, specifically with respect to body composition, glucose utilization, resting blood pressure, blood lipid profiles, vascular condition, gastrointestinal transit, bone mineral density, postcoronary function, COPD function, low back pain, arthritis, depression, metabolic syndrome, cardiovascular disease, and all-cause mortality. It is, therefore, recommended that strength exercise be included in programs for fat loss and health enhancement.
CONDENSED VERSION AND BOTTOM LINE
Sedentary living leads to muscle loss, metabolic slowdown, and fat gain. Presently, almost 70% of American adults are overfat and at increased risk for chronic diseases and other health problems. Dieting is a popular but ineffective approach for attaining permanent fat loss, and regular endurance exercise is performed by less than 5% of the adult population. Basic and brief strength training sessions have proved to be effective for rebuilding muscle, recharging metabolism, reducing fat, and enhancing a variety of health and fitness factors. The ACSM strength training guidelines provide a practical protocol for reversing degenerative processes and for eliciting physiological and psychological improvements that positively impact quality of life.
1. American College of Sports Medicine. Guidelines for Graded Exercise Testing and Exercise Prescription
. 5th ed. Philadelphia (PA): Lea & Febiger; 1995. pp. 172-5.
2. American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription
. 7th ed. Philadelphia (PA): Lippincott, Williams and Wilkins; 2006. pp. 154-8.
3. Annesi JJ, Westcott WL, Gann S. Preliminary evaluation of a 10-week resistance and cardiovascular exercise protocol on physiological and psychological measures for a sample of older women. Percept Mot Skills
4. Annesi JJ, Westcott WL. Relations of physical self-concept and muscular strength with resistance exercise
-induced feeling state scores in older women. Percept Mot Skills
5. Ballor D, Poehlman E. Exercise training enhances fat-free mass preservation during diet-induced weight loss
: A meta analytic finding. Int J Obes.
6. Boyden T, Pamenter R, Going S, et al
. Resistance exercise
training is associated with decreases in serum low-density lipoprotein cholesterol levels in premenopausal women. Arch Intern Med.
7. Braith RW, Stewart KJ. Resistance exercise
training: Its role in the prevention of cardiovascular disease. Circulation
8. Broeder CE, Burrhus KA, Svanevik LS, Wilmore JH. The effects of either high-intensity resistance or endurance training on resting metabolic rate. Am J Clin Nutr.
9. Campbell WW, Crim MC, Young RV, Evans WJ. Increased energy requirements and changes in body composition with resistance training in older adults. Am J Clin Nutr
10. Fiatarone MA, O'Neil EF, Ryan ND, et al
. Exercise training and nutritional supplementation for physical frailty in very elderly people. N Engl J Med.
11. Forbes GB. The adult decline in lean body mass. Hum Biol.
12. Frontera WR, Hughes VA, Lutz KJ, Evans WJ. A cross-sectional study of muscle strength and mass in 45 to 78 yr-old men and women. J Appl Physiol.
13. Frontera WR, Hughes VA, Fielding RA, Fiatarone MA, Evan EJ, Roubenoff, R. Aging of skeletal muscle: A 12-yr longitudinal study. J Appl Physiol.
14. Geliebter A, Maher MM, Gerace L, Gutin B, Heymsfield SB, Hashim SA. Effects of strength or aerobic training of body composition, resting metabolic rate, and peak oxygen consumption in obese dieting subjects. Am J Clin Nutr.
15. Gettman LR, Ayres JJ, Pollock ML, Jackson A. The effects of circuit weight training on strength, cardiorespiratory function, and body composition of adult men. Med Sci Sports Exerc.
16. Gettman LR, Ward P, Hagan RD. A comparison of combined running and weight training with circuit weight training. Med Sci Sports Exerc.
17. Ghiladucci L, Holly R, Amsterdam E. Effects of high resistance training in coronary heart disease. Am J Cardiol.
18. Hackney KJ, Engels HJ, Gretebeck RJ. Resting energy expenditure and delayed-onset muscle soreness after full-body resistance training with an eccentric concentration. J Strength Cond Res.
19. Harris K, Holly R. Physiological response to circuit weight training in borderline hypertensive subjects. Med Sci Sports Exerc.
20. Haskell WL, Lee IM, Pate RR, et al
. Physical activity
and public health: Updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Circulation
21. Hoff J, Tjonna AE, Steinshamn S, Hoydal M, Richardson RS, Helgerud J. Maximal strength training of the legs in COPD: A therapy for mechanical inefficiency. Med Sci Sports Exerc.
22. Hunter GR, Wetzstein CJ, Fields DA, et al
. Resistance training increases total energy expenditure and free-living physical activity
in older adults. J Appl Physiol.
23. Hurley BF, Roth SM. Strength training in the elderly: Effects on risk factors for age-related diseases. Sports Med.
24. Jurca R, LaMonte MJ, Church TS, et al
. Associations with muscle strength and aerobic fitness with metabolic syndrome in men. Med Sci Sports Exerc.
25. Kelemen M, Stewart K, Gillilan R, et al
. Circuit weight training in cardiac patients. JACC
26. Keys A, Taylor HL, Grande F. Basal metabolism and age of adult man. Metabolism
27. Koffler KH, Menkes A, Redmond RA, Whitehead WE, Pratley RE, Hurley BF. Strength training accelerates gastrointestinal transit in middle-aged and older men. Med Sci Sports Exerc
28. Mann T, Tomiyama AJ, Westling E, Lew AM, Samuels B, Chatman J. Medicare's search for effective obesity treatments: Diets are not the answer. Am Psychol
29. Marks R. The effect of isometric quadriceps strength training in mid-range for osteo-arthritis of the knee. Arthritis Care Res.
30. Marzolini S, Oh PI, Thomas SG, Goodman JM. Aerobic and resistance training in coronary disease: Single versus multiple sets. Med Sci Sports Exerc.
31. Mason C, Brien SE, Craig CL, Gauvin L, Katzmarzyk PT. Musculoskeletal fitness and weight gain. Med Sci Sports Exerc
32. Menkes A, Mazel S, Redmond R, et al
. Strength training increases regional bone mineral density and bone remodeling in middle-aged and older men. J Appl Physiol.
33. Messier SP, Dill ME. Alterations in strength and maximal oxygen uptake consequent to Nautilus circuit weight training. RQES
34. Miller JP, Pratley RE, Goldberg AP, et al
. Strength training increases insulin action in healthy 50 to 65 year-old men. J Appl Physiol.
35. Nelson ME, Fiatarone MA, Morganti CM, Trice I, Greenberg RA, Evans WJ. Effects of high-intensity strength training on multiple risk factors for osteoporotic fractures. JAMA
36. Ogden CL, Carroll MD, Curtin, et al
. Prevalence of overweight and obesity in the United States 1999-2004. JAMA
37. Olshansky SJ, Passaro DL, Hershow RC, et al
. A potential decline in life expectancy in the United States in the 21st century. N Engl J Med.
38. Olson TP, Dengel DR, Leon AS, Schmitz KH. Moderate resistance training and vascular health in overweight women. Med Sci Sports Exerc.
39. Perri MG, Fuller PR. Success and failure in the treatment of obesity: Where do we go from here? Med Exerc Nutr Health
40. Phillips SM. Resistance exercise
: Good for more than just Grandma and Grandpa's muscles. Appl Physiol Nutr Metab.
41. Pratley RB, Nicklas M, Rubin J, et al
. Strength training increases resting metabolic rate and norepinephrine levels in healthy 50-65 year-old men. J Appl Physiol.
42. Risch S, Nowell N, Pollock M, et al
. Lumbar strengthening in chronic low-back pain patients. Spine
43. Schmitz KH, Hannan PJ, Stovitz SD, Bryan CJ, Warren M, Jensen MD. Strength training and adiposity in premenopausal women: Strong, healthy and empowered study. Am J Clin Nutr.
44. Singh N, Clements K, Fiatarone M. A randomized controlled trial of progressive resistance training in depressed elders. J Gerontol.
45. Skender ML, Goodrick GK, Del Junco DJ, et al
. Comparison of 2-year weight loss
trends in behavioral treatments of obesity: Diet, exercise, and combination interventions. JADA
46. Taaffe DR, Pruitt L, Reim J, Butterfield G, Marcus R. Effect of sustained resistance training on basal metabolic rate in older women. JAGS
47. Troiano RP, Berrigan D, Dodd KW, Masse LC, Tilert T, McDowell M. Physical activity
in the United States measured by accelerometer. Med Sci Sports Exerc
48. U.S. Department of Health and Human Services. Physical Activity and Health: A Report of the Surgeon General.
Atlanta, GA. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion; 1996.
49. Westcott WL, Winett RA. Applying the ACSM guidelines. Fitness Manage.
50. Westcott WL, Annesi JJ, Skaggs JM, Gibson JR, Reynolds RD. Comparison of two exercise protocols on fitness score improvement in poorly conditioned Air Force personnel. Percept Mot Skills
51. Westcott WL, Martin WF, Loud RL, Stoddard S. Research update: Protein and body composition. Fitness Manage
52. Wijndaele K, Duvigneaud N, Matton L, et al.
Muscluar strength, aerobic fitness, and metabolic syndrome risk in Flemish adults. Med Sci Sports Exerc.
53. Wolfe RR. The unappreciated role of muscle in health and disease. Am J Clin Nutr.
American College of Sports Medicine. ACSM
's Guidelines for Exercise Testing and Prescription
. 7th ed. Philadelphia (PA): Lippincott, Williams and Wilkins; 2006.
American College of Sports Medicine. Appropriate physical activity
intervention strategies for weight loss
and prevention of weight regain for adults, position stand. Med Sci Sports Exerc
Keywords:© 2009 American College of Sports Medicine
Muscular Conditioning; Physical Activity; Resistance Exercise; Risk Factor Reduction; Weight Loss