Effect of Weekly Exercise Frequency on BMI. Dalton Trembow Rowan University Department of Health and Exercise Science

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1 Effect of Weekly Exercise Frequency on BMI Dalton Trembow Rowan University Department of Health and Exercise Science

2 BACKGROUND AND LITERATURE REVIEW It is well known that obesity has become an epidemic level issue in the Unites States, with about two thirds of Americans being overweight (BMI kg/m 2 ) or obese (BMI 30 kg/m 2 ) (1). Being overweight or obese can give rise to many comorbid conditions such as cardiovascular disease, diabetes, stroke, and cancer (1). With such a large proportion of the population being affected, there has been significant emphasis placed on the research and management of obesity. When considering that cardiovascular disease is the number one cause of death in the United States, it becomes clear how significant this issue has become (1). Body composition, the ratio of lean tissue to fat tissue, is a modifiable risk factor (4). It can be measured and monitored several different ways, body mass index (BMI), being one of the more common methods. BMI uses the total body mass and height of the individual to generate a number that can then be used to categorize the individual as normal, overweight, or obese (<25, , and 30 respectively) (2). BMI does have limitations, namely that it does not distinguish between lean mass and fat mass in its calculations, but it is still a valuable tool to help the average individual understand their risk level. Unlike age, sex, or genetics, body composition is a modifiable risk factor. This means that body composition can be changed, and the negative effects of poor body composition are mitigated. Body composition management, in this case weight loss, is typically achieved through a combination of diet and exercise. To shed unwanted fat, the body must have a negative net caloric intake so that it will break down fats for energy (4). Put simply, more calories must be used than are consumed. Therefore, being conscious of how much food is consumed and maximizing the number of calories burned with exercise is the optimal way to reduce body fat.

3 Understanding the fundamentals of exercise physiology, how the body responds to exercise, is essential when considering a weight loss program. Exercise is helpful in shedding unwanted fat because it increases caloric expenditure. When more calories are burned than consumed in a given day, the body will break down fats to make up the difference and sustain itself. One pound of fat is equivalent to 3,500 calories, meaning there must be a 500-calorie deficit each day to lose one pound of fat per week (4). Aiming to lose one to two pounds of fat per week is generally recommended to avoid putting unsafe stress on the body, and result in lasting change. Fad diets and rapid cleanses may result in quick weight loss, but its most often accompanied by quick weight gain once the individual returns to their normal lifestyle. Therefore, emphasis on weight loss as a gradual process is key to produce successful and lasting results. While all exercise has some benefit, different intensities and durations of exercise are more efficient than others are reaching specific goals. In the case of weight loss, aerobic exercise is by far the most effective mode of exercise (4). Aerobic exercise utilizes oxygen, whereas anaerobic exercise does not; maximizing endurance (moderate intensity) and power (high intensity) performance respectively (4). Aerobic exercise is best for weight loss because it can be performed for a longer duration at a moderate intensity and utilize fat as a fuel source. When exercise first begins, the body burns almost exclusively carbohydrates because they can be utilized quickly and are readily available for use in the form of glycogen stored in the muscles (4). The breakdown of fats for fuel is a longer process than using carbohydrates but is much more efficient, providing more than double the number of calories per gram (4). As exercise continues, the body slowly begins to burn fats along with carbohydrates until eventually fats become the sole fuel source utilized. This conversion from carbohydrate to fat metabolism

4 typically takes 40 minutes of continuous, moderate exercise (4). This conversion time can be decreased through training, with endurance athletes such as runners or cyclists making the conversion much faster than the average individual (4). Although there are many other variables and complexities to consider, having a basic understanding of this concept illustrates how the duration of exercise can affect the outcome on the body. While the effects of intensity and duration of exercise are well documented, there is minimal research concerning the frequency at which exercise is performed. Most guidelines recommend activity should be performed on all or most days of the week, however the results of a randomized clinical trial in Iran suggest that a lower weekly frequency of activity may be more effective for weight loss (3). The purpose of this study was to examine the effect of the frequency of weekly exercise sessions, without altering the total exercise time, on BMI score over a four-week period. METHODS Study participants included 30 Rowan University undergraduate students, both male and female, ages years old. The BMI s of participants were all overweight or very close to overweight. BMI was chosen for measuring and tracking weight loss because it is easy to understand and requires no training to measure properly. Participants were selected based on willingness to participate, desire to lose weight, and ability to perform moderate aerobic exercise. The study was a four week, single-blind randomized clinical trial. Participants were separated into low frequency exercise and high frequency exercise groups. Group assignments were completed using a computer-generated random numbers method. All 30 participants were brought into the Rowan University exercise physiology lab for instruction and baseline measurements at the beginning of the program. Participants were given their group assignments

5 upon arrival and separated into their respective groups. To make the process run more smoothly, one group was brought to a separate classroom for instruction while the other group had their baseline measurements taken. Once measurements were completed the groups switched locations to complete the other half of their orientation. Instruction was delivered verbally by the project manager. Basic printed instructions were distributed at this time as well as sent to each participant s to ensure comprehension and retention of the information, even if the printed instructions were lost. Participants were instructed to complete 150 minutes of moderate aerobic exercise each week. A list of approved exercises was provided in the instruction materials including walking/jogging, elliptical machine, and cycling. Moderate exercise was defined to participants as 40% to 60% of your maximum effort. Participants were encouraged to use fitness trackers or heart rate monitors if they desired, but it was not a requirement. Adhering to moderate intensity using perceived exertion was acceptable. The low frequency group was instructed to complete their 150 minutes of exercise weekly over 2-3 days, whereas the high intensity group was instructed to take 4-5 days to complete the same 150 minutes of exercise. After instruction was complete all participants questions and concerns were answered and addressed. In addition to instruction, baseline measurements of participants BMI scores were recorded using the BMI testing protocol developed by the project manager. The simple protocol did not require additional preparation or training to complete. Measurement was completed using a digital fitness scale with height rod. Measurements were taken and recorded by two Rowan University exercise science graduate students to ensure accuracy and efficiency during the process. The same two students took these measurements again in the same location at the end of the program four weeks later to minimize inconsistencies in testing protocol.

6 INSTRUMENTATION The following step-by-step BMI testing protocol was developed by the project manager to ensure accurate and uniform measurement of all participants. The protocol was reviewed with the two graduate students administering the test by the project manager, and a printed version was provided during testing for reference. All measurements were recorded in Table 1 (see results). Calculations were completed using Microsoft Excel after inputting the data. BMI Testing Protocol Step 1: Measure the participant s weight by having them stand on the scale. Only light clothing should be worn. Record the result in pounds. Step 2: Measure the participant s height using the height rod. Participant should stand straight with feet flat and back towards the height rod. No shoes or other footwear should be worn. Socks are acceptable. Record the result in inches. Step 3: Calculate BMI using the following formula. BMI = [weight (lb) / [height (in)] 2 ] x 703 RESULTS Participant heights and weights were measured accurately and recorded with means of 64.3 ± 1.49 in and ± lbs respectively. There was a slight reduction in weight after the four-week program, with a post weight mean of ± lbs. In the low frequency exercise group, there was a significant reduction in BMI (p = ) from ± 1.1 to ± 0.94 kg/m 2. Conversely, there was no significant reduction in the high frequency exercise group BMI (p = ) from ± 1.24 to ± 1.23 kg/m 2.

7 Table 1: Displays height (in) and pre/post weights (lbs) for all participants. Participant Height (in) Pre Weight (lbs) Post Weight (lbs) Mean SD

8 Table 2: Displays pre and post program BMI scores for low and high frequency exercise groups. Low (2-3 days/week) Exercise Frequency High (4-5 days/week) Participant Pre BMI Post BMI Participant Pre BMI Post BMI Mean Mean SD SD p-value p-value Figure 1: Illustrates the change in BMI for each participant of the low frequency exercise group.

9 Figure 2: Illustrates the change in BMI for each participant of the high frequency exercise group. DISCUSSION While both the low and high frequency exercise groups had a reduction in average BMI, only the low frequency group showed a statistically significant change. This demonstrates that despite exercising for the same 150 minutes each week, completing the exercise at a lower weekly frequency was significantly more effective in achieving weight loss and BMI reduction. This contradicts the current guidelines and recommendations which suggest exercise should be preformed on most or all days of the week to promote weight loss. A likely reason for the success of the low frequency exercise group is the increased duration of their exercise bouts. To complete the required 150 minutes per week in just two or three days means their exercise sessions were 50 to 75 minutes in duration; whereas the high frequency group sessions were 30 to 37.5 minutes on four or five days weekly. This explains why there was a significant difference between the two groups. Conversion from carbohydrate metabolism to fat metabolism usually takes at least 40 minutes, meaning the low frequency group spent time each session burning exclusively fats. On the other hand, the high frequency group was only beginning to complete this conversion before ending their sessions. Therefore,

10 the low frequency group spent significantly more time each week utilizing their fat metabolism. This is likely why the low frequency group had a significantly greater reduction in BMI despite exercising for the same 150 total minutes each week. Although the study was a success, there were many variables unaccounted for that could have had an affect on the results, namely nutrition. This study did not monitor or manipulate the diet of the participants in any way. Participants were instructed to continue with their normal diet, but it is possible that some participants made healthier changes to their diet during the program because they were motivated to lose weight. Future studies that either control or monitor diet would gleam further insight into the influence of exercise frequency on weight loss. The other main limitations of the study were time and sample size. One month is not a very long time because weight loss is a very gradual process, and 30 individuals does not provide much statistical power. Therefore, the study would greatly benefit from implementing it over a much longer period with more participants. Overall the study was a success and serves as a proof of concept for research regarding the frequency of exercise and its effect on weight loss. Since implementation of the study was simple and very inexpensive, there is great potential for expansion and future research.

11 References (1) Janney, C. A., & Jakicic, J. M. (2010). The influence of exercise and BMI on injuries and illnesses in overweight and obese individuals: a randomized control trial. The International Journal of Behavioral Nutrition and Physical Activity, 7, 1. (2) Kelley, G. A., Kelley, K. S., & Pate, R. R. (2014). Effects of exercise on BMI z-score in overweight and obese children and adolescents: a systematic review with metaanalysis. BMC Pediatrics, 14, (3) Madjd, A., Taylor, M.,A., Shafiei Neek, L., Delavari, A., Malekzadeh, R., Macdonald, I.,A., & Farshchi, H.,R. (2016). Effect of weekly physical activity frequency on weight loss in healthy overweight and obese women attending a weight loss program: A randomized controlled trial. The American Journal of Clinical Nutrition, 104(5), /ajcn [doi] (4) Suleman, A., MD. (2017, January 06). Exercise Physiology. Retrieved from