Obesity and inactivity are the largest modifiable risk factors for disease. The National Institute of Health estimates that 65% of Americans are “overweight” or “obese,” and therefore over 190 million Americans live with the second most dangerous risk factor for disease (1,2,5,7,15,16,22,29,30). Obesity is often described as an epidemic, and it is considered the “fastest growing risk factor” in Western society (15,25,30). The hypothesis of this study was that compliance with the U.S. Surgeon General's guidelines for exercise would alone achieve a significant change in body fat mass.
Exercise is commonly prescribed to prevent or reduce disease (3-7,9,11,14,16,24-31) because exercise/fitness has shown to lead to a substantial decrease in mortality in comparison with obesity's role as a predictor of disease (7,22). Studies have shown a significant correlation between increased physical activity and decreased health risk (3,22,30), and a study by Irwin et al. (16) showed the specific effect of exercise on intra-abdominal fat in postmenopausal women. One hundred seventy-three sedentary, overweight women (body fat > 46%) were recruited for Irwin et al.'s study, and subjects were randomly assigned to an exercise intervention group (n = 87) or a control group (n = 86). The body fat percentage was calculated with dual-energy x-ray absorptiometry and computerized tomography scans and conducted upon enrollment and after 3 and 12 months. The subjects in this study who were adherent to the exercise intervention of 45 minutes of moderate-intensity exercise 5 days per week for 12 months showed a significant reduction in intra-abdominal body fat (p = 0.01), body mass index (p = 0.04), and hip circumference (p = 0.01), whereas the control group had gains in total body fat.
Many studies suggest physical activity and exercise to benefit one's health (5,8,12,14,16-18,24-26,29), but few studies have offered specific protocols for frequency, intensity, or duration with specific testing to show how prescribed exercise affects subjects' body fat (12,25,26). A study by Blair and Church (5) evaluated intensity of exercise with mortality risk, and at the conclusion of their article they suggested the need for a clinical trial to measure the outcomes from physical activity. The purpose of this study is to examine the changes in body fat mass of previously sedentary, deconditioned subjects who began following the U.S. Surgeon General's recommendation for frequency of exercise.
Experimental Approach to the Problem
Testing of the body fat mass was accomplished with air displacement plethysmography (10,12,13,21,26-28) before and after an 8-week exercise regime was completed. This testing measures percent fat and fat-free mass through testing of mass and volume. The exercise regime prescribed (in adherence with the U.S. Surgeon General's guidelines) was either 30 minutes of continuous exercise on cardiovascular equipment or 30 minutes of continuous exercise with use of a 10-piece circuit system, and both exercise protocols were to be accomplished at 70% of each subject's maximum heart rate (HR). Heart rate of each performance was recorded.
Ninety volunteer subjects of both sexes and 4 ethnicities were recruited for this study (Table 1). All subjects were given a medical screening questionnaire and screened for untreated diseases ranging from arthritis to peripheral vascular disease. Once cleared by a physician for participation in the regular exercise of this study, all subjects were briefed on the risks involved in this study, and each subject signed a written informed consent as required by the Austin Wellness Institutional Review Board, in conformation to the Declaration of Helsinki. All subjects were over 18 years of age, and 2 subjects were eliminated for possible undiagnosed cardiovascular disease.
All subjects who participated had been previously sedentary and “deconditioned.” This was determined from data they provided in listing the previous frequency of exercise per month for the past year. Each person enrolled had not exercised more than once per week for over the past year. Their initial body fat percentages were “risky” (>30% for men and >40% for women) or “moderately fat” (>25% for men and >35% for women). Eight subjects were eliminated from the study because they did not complete the final BodPod (Life Measurements, Inc., Concord, CA, USA) test within 7 days after completing the 8-week study. This study was designed to analyze compliance of previously sedentary, deconditioned subjects according to the U.S. Surgeon General's guidelines for frequency of exercise.
The duration of this study was 8 weeks, and subjects were prescribed a protocol matching the U.S. Surgeon General's recommendation for frequency of exercise (8), which was to exercise “most days of the week” for 30 minutes of continuous, moderately intense exercise. The exercise regime prescribed was 4 times per week, but subjects were not prohibited from exercising more frequently, and any additional training was of their own design of intensity and time.
Subjects were told to train at 70% of each person's maximum HR, on either cardiovascular equipment on through continuous use of a 10-piece circuit system. The 70% HR prescribed was calculated with the following equation: (220 - Age) x .70 = target HR. Subjects' HR were recorded on the cardio equipment or with a Polar (Lake Success, NY, USA) HR monitor for subjects exercising in circuit training. This was the intensity measured for compliance, and no dietary changes were prescribed. BodPod reliability tests were performed daily with a standardized metal chamber for validation of mass, volume, and density.
After completion of this study, subjects were categorized on the basis of voluntary compliance to the protocol of exercising 4 times a week. The categories were as follows: 20 control subjects who chose to not exercise at all; 20 subjects who exercised less than 2 times per week; 20 subjects who exercised 2 to 3 times/week; 20 subjects who exercised 4 times or more per week (with ≥90% compliance). Compliance was tracked using the EFit program for attendance, as reported at the wellness center. This electronic attendance program tracked attendance and duration. Two-a-day exercise sessions were counted as 2 separate bouts of exercise.
The dependent variable in this study was the body fat mass, as determined through air displacement plethysmography with the BodPod. This testing method has been shown to be reliable and valid in previous studies (10,12,13,21,26-28). The body fat masses, attendance data, and demographic data were recorded in the Microsoft Excel (Redmond, WA, USA) program (Table 2). The data were analyzed using a repeated measures analysis of variance with the InStat GraphPad software (La Jolla, CA, USA). All statistical tests were performed at an alpha level of 0.05.
There was a significant difference in body fat mass in this study (p = 0.016, F = 2.561) (Figure 1), and the only group that showed a difference in a two-tailed t-test was the group that exercised 4 or more times per week (p = 0.004, t = 3.010). There was not a significant difference among sexes or ages (p > 0.05). This showed that exercising 4 or more times per week yielded a decrease in body fat mass in this 8-week study; the mean loss for this group was 13.3 lbs (Table 2).
This study examined frequency as 1 specific variable in exercise to reduce one's body fat mass. This exercise protocol could be considered an initial step in a preventive modality for obesity, which is a high risk factor of disease (3,5-7,11,16,24,29-30). Had this study been of a longer duration, other variables such as dietary changes or differences in duration or intensity of exercise may have also yielded a significant reduction in body fat mass, but results of this study were in accordance with the advice of the U.S. Surgeon General and the Centers for Disease Control (8). This study was designed to focus exclusively on frequency of exercise to achieve initial changes in the body fat mass of previously sedentary, deconditioned subjects.
This study confirmed a previous study's results (16) which showed that frequency is responsible for body fat loss rather than intensity or duration. The experimental design intentionally included subjects' voluntary compliance because this reflects the compliance to both prescribed and self-directed programs. The control group in this study chose continuation of inactivity, and this may be the same population that chooses to continually ignore the benefits that exercise has on one's health. This study revealed that just 30 minutes of continuous exercise at 4 times per week yielded a significant change in body fat mass for these previously sedentary subjects (Table 3). This shows the efficacy of the protocol suggested by the U.S. Surgeon General, and it could be prescribed to reduce the risk of disease (3,5,7,11,14,15,18,29,30) and begin a lifelong increase in fitness.
Special thanks given to all subjects who volunteered for this study from the former Austin Wellness Center and from Austin Independent School District. We also thank Dr. Willis' undergraduate student, Ms. Roberta Gonzalez, who was responsible for all of the BodPod testing in this study. This study was conducted independent of any funding, participation, or affiliation from the equipment companies, and thereby was exempt of conflict if interest.
1. Batsis, JA, Romero-Corral, A, Collazo-Clavell, ML, Sarr, MG, Somers, VK, Brekke, L, and Lopez-Jimenez, F. Effect of weight loss on predicted cardiovascular risk: change in cardiac risk after bariatric surgery. Obesity
15: 772-784, 2007.
2. Blair, SN, Booth, M, Gyarfas, I, Iwane, H, Marti, B, Matsudo, V, Morrow, MS, Noakes, T, and Shepard, R. Development of public policy and physical activity initiatives internationally. Sports Med
21: 157-163, 1996.
3. Blair, SN and Brodney, S. Effects of physical inactivity and obesity on morbidity and mortality: current evidence and research issues. Med Sci Soprts Exerc
31: S646-S662, 1999.
4. Blair, SN, Chandler, JV, Ellisor, DB, and Langley, T. Improving physical fitness by exercise training programs. South Med J
73: 1594-1596, 1980.
5. Blair, SN and Church, TS. The fitness, obesity, and health equation: is physical activity the common denominator? JAMA
292: 1232-1234, 2004.
6. Blair, SN, Kohl, HW III, Barlow, CE, Paffenbarger, RS Jr, Gibbons, LW, and Macera, CA. Changes in physical fitness and all-cause mortality. A prospective study of healthy and unhealthy men. JAMA
273: 1093-1098, 1995.
7. Blair, SN, Kohl, HW III, Paffenbarger, RS Jr, Clark, DG, Cooper, KH, and Gibbons, LW. Physical fitness and all-cause mortality. A prospective study of healthy men and women. JAMA
262: 2395-2401, 1989.
9. Daley, AJ, Copeland, RJ, Wright, NP, Roalfe, A, and Wales, JK. Exercise therapy as a treatment for psychopathologic conditions in obese and morbidly obese adolescents: a randomized, controlled trial. Pediatrics
118: 2126-2134, 2006.
10. Davis, JA, Dorado, S, Keays, KA, Reigel, KA, Valencia, KS, and Pham, PH. Reliability and validity of the lung volume measurement made by the BOD POD body composition system. Clin Physiol Funct Imaging
27: 42-46, 2007.
11. Eisenmann, JC, Wickel, EE, Welk, GJ, and Blair, SN. Relationship between adolescent fitness and fatness and cardiovascular disease risk factors in adulthood: the Aerobics Center Longitudinal Study (ACLS). Am Heart J
149: 46-53, 2005.
12. Fillipas, S, Oldmeadow, LB, Bailey, MJ, and Cherry, CL. A six-month, supervised, aerobic and resistance exercise program improves self-efficacy in people with human immunodeficiency virus: A randomized controlled trial. Aust J Physiother
52: 185-190, 2006.
13. Ginde, SR, Geliebter, A, Rubianof, A, Silva, AM, Wang, J, Heshka, S, and Heymsfield, SB. Air displacement plethysmography
: validation in overweight and obese subjects. Obes Res
13: 1232-1237, 2005.
14. Herman, CW, Musich, S, Lu, C, Sill, S, Young, JM, and Edington, DW. Effectiveness of an incentive-based online physical activity intervention on employee health status. J Occup Environ Med
48: 889-895, 2006.
15. Hu, FB. Overweight and Obesity in Women: Health Risks and Consequences. J Womens Health
12: 163-172, 2003.
16. Irwin, ML, Yasui, Y, Ulrich, CM, Bowen, D, Rudolph, RE, Schwartz, RS, Yukawa, M, Aiello, E, Potter, JD, and Mctiernan, A. Effect of exercise on total and intra-abdominal body fat in postmenopausal women: a randomized controlled trial. JAMA
289: 323-330, 2003.
17. Jakicic, JM, Marcus, BH, Gallagher, KI, Napolitano, M, and Lang, W. Effect of exercise duration and intensity on weight loss in overweight, sedentary women: a randomized trial. JAMA
. 290: 1323-1330, 2003.
18. Jahicic, JM and Otto, AD. Treatment and prevention of obesity: what is the role of exercise? Nutr Rev
64: S57-S61, 2006.
19. Kraemer, WJ, Torine, JC, Silvestre, R, French, DN, Ratamess, NA, Spiering, BA, Hatfield, DL, Vingren, JL, and Volek, JS. Body size and composition of National Football League players. J Strength Cond Res
19: 485-489, 2005.
20. Mccullough, PA, Gallagher, MJ, Dejong, AT, Sandberg, KR, Trivax, JE, Alexander, D, Kasturi, G, Jafri, SM, Krause, KR, Chengelis, DL, Moy, J, and Franklin, BA. Cardiorespiratory fitness and short-term complications after bariatric surgery. Chest
130: 517-525, 2006.
21. Minderico, CS, Silva, AM, Teixeira, PJ, Sardinha, LB, Hull, HR, and Fields, DA. Validity of air-displacement plethysmography in the assessment of body composition changes in a 16-month weight loss program. Nutr Metab (Lond)
3: 32, 2006.
22. Moras, A, Lee, I, Buring, JE, and Ridker, PM. Association of physical activity and body mass index with novel and traditional cardiovascular biomarkers in women. JAMA 295: 1412-1419, 2006.
23. Noreen, EE and Lemon, PW. Reliability of air displacement plethysmography
in a large, heterogeneous sample. Med Sci Sports Exerc
38: 1505-1509, 2006.
24. Pescatello, LS. Exercise and hypertension: recent advances in exercise prescription. Curr Hypertens Rep
. 7: 281-286, 2005.
25. Shaw, I and Shaw, BS. Consequences of resistance training on body composition and coronary artey disease risk. Cardio J So Africa
17: 111-116, 2006.
26. Tucker, La and Peterson, Tr. Objectively measured intensity of physical activity and adiposity in middle-aged women. Obes Res.11: 1581-1587, 2003.
27. Voelker, R. Studies suggest dog walking a good strategy for fostering fitness. JAMA
296: 643, 2006.
28. Volaklis, KA, Douda, HT, Kokkino, PF, and Tokmakidis, SP. Physiological alterations to detraining following prolonged combined strength and aerobic training in cardiac patients. Eur J Cardiovasc Prev Rehabil
13: 375-380, 2006.
29. Warburton, DE, Nicol, CW, and Bredin, SS. Health benefits of physical activity: the evidence. CMAJ
174: 801-809, 2006.
30. Wessel, TR, Arant, CB, Olson, MB, Johnson, BD, Reis, SE, Sharaf, BL, Shaw, LJ, Handberg, E, Sopko, G, Kelsey, SF, Pepine, CJ, and Merz, NB. Relationship of physical fitness vs body mass index with coronary artery disease and cardiovascular events in women. JAMA
292: 1179-1187, 2004.
31. Writing Group for the Activity Counseling Trial Research Group. Effects of physical activity counseling in primary care. The Activity Counseling Trial: a randomized controlled trial. JAMA
286: 677-687, 2001.