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Frequency of Exercise for Body Fat Loss: A Controlled, Cohort Study

Willis, F Buck1; Smith, Forrest M2; Willis, Adele P3

Journal of Strength and Conditioning Research: November 2009 - Volume 23 - Issue 8 - p 2377-2380
doi: 10.1519/JSC.0b013e3181b8d4e8
Original Research
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Willis, FB, Smith, FM, and Willis, AP. Frequency of exercise for body fat loss: a controlled, cohort study. J Strength Cond Res 23(8): 2377-2380, 2009-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 in frequency of exercise. Ninety subjects of both sexes were recruited; ages ranged from 22 to 74 (mean 37.5 ± 13) years. Subjects were prescribed exercise of 4 times a week, 30 minutes of continuous exercise, for 8 weeks. Eighty subjects completed the 8-week study and were categorized based on voluntary compliance: control (no exercise); exercise less than 2 times/week; exercise 3 to 4 times/week; exercise 4 or more times/week. Body fat mass was the dependent variable in this study, as measured by air displacement plethysmography, and data analysis was accomplished with a repeated measures analysis of variance. There was a significant change in body fat mass in this study, but the only significant difference between groups was for the group that exercised 4 or more times/week, (p = 0.004). Adherence to the U.S. Surgeon General's Guidelines for frequency of exercising 4 times per week for 30 minutes was effective in reducing subjects' body fat mass in this study.

1Dynasplint Systems, Landmark Medical, Austin, Texas; 2Smith Pediatrics; and 3Austin Wellness Center, Austin, Texas

Address correspondence to Dr. Buck Willis, buckphd@yahoo.com.

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Introduction

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.

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Methods

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.

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Subjects

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.

Table 1

Table 1

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.

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Procedures

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.

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Statistical Analyses

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.

Table 2

Table 2

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Results

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).

Figure 1

Figure 1

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Discussion

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.

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Practical Applications

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.

Table 3

Table 3

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Acknowledgments

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.

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    Keywords:

    air displacement plethysmography; body composition change; Surgeon General's exercise recommendations

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