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Original Research |
Department of Physical Education and Health Promotion, University of WisconsinOshkosh Oshkosh, Wisconsin (W.D.S.)
Northern Michigan University, Marquette, Michigan (C.J.B.)
Arizona State University, Tempe, Arizona (L.K.K.)
Address reprint requests to: Dr. W. Daniel Schmidt, Department of Physical Education and Health Promotion, Albee Hall, The University of WisconsinOshkosh, Oshkosh, WI 54901. E-mail: schmidtw{at}uwosh.edu.
| ABSTRACT |
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Methods: Overweight, female college students (body mass index
28 kg/m2) were recruited and assessed at baseline and post-treatment for aerobic fitness (Astrand maximal cycle test), weight, skinfold thickness (7-site), and circumference measures (4-site). Following measurement of resting energy expenditure (REE), subjects were asked to follow a self-monitored calorie restricted diet (80% of REE) for the twelve week duration of the study and were assigned (non-random) to one of four treatment groups: 1) a nonexercising control group (control, n = 8), 2) a 30 minutes continuous exercise group (1 x 30, n = 12), 3) a 30 minutes accumulated exercise group (2 x 15, n = 10) and 4) a second 30 minutes accumulated exercise group (3 x 10, n = 8). The exercising subjects participated in aerobic exercise training at 75% of heart rate reserve three to five days per week with all exercise monitored.
Results: VO2 max increased significantly while weight, body mass index, sum of skinfolds, and sum of circumferences decreased significantly from baseline to post-treatment in the 1 x 30, 2 x 15 and the 3 x 10 groups, but not in the control group. A tertiary finding was that exercise participation did not differ among the exercising groups with regard to the average number of days per week.
Conclusions: These results support the hypothesis that exercise accumulated in several short bouts has similar effects as one continuous bout with regard to aerobic fitness and weight loss during caloric restriction in overweight, young women.
Key words: aerobic fitness, heart rate reserve, body mass index
| INTRODUCTION |
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The ACSM and CDC guidelines therefore stipulated that every American adult should accumulate thirty minutes or more of moderate intensity physical activity over the course of most days of the week [1,3]. These recommendations were, of course, clarified further in 1996 with the Surgeon Generals Report on Physical Activity and Health [4]. This approach is seemingly more practical in terms of creating a more attainable level of activity for the previously sedentary individual (i.e., shorter bouts can be done more frequently) as well as the individual who has difficulty fitting activity into their daily schedule. However, the effectiveness of this guideline as it pertains to cardiovascular fitness and weight loss is still controversial.
With the current body of available data [512], there appears to be general agreement that multiple short bouts of exercise per day can potentially increase aerobic capacity and may also be an effective method for weight loss though the magnitude of these benefits is unclear. A common limitation, however, of the published research comparing several short exercise bouts to one longer continuous bout is that investigations have relied on self-reported exercise behavior. With the exception of the apparently active young men in the Ebisu [5] paper, subjects have been unsupervised. Yet research has shown that self-reported physical activity is often an imperfect estimate of the actual amount of physical activity an individual may perform [13]. Moreover, accurate reports of physical activity may be more difficult with multiple short exercise bouts because of the added cognitive demand of remembering multiple behaviors each day. If shorter bouts of exercise are indeed an effective means for improving overall health and fitness, it seems imperative to verify both the intensity and the actual time spent exercising. Furthermore, only three of the aforementioned studies [8,9,12] compared their exercising subjects to nonexercising controls as part of the study design. Therefore, the purpose of this study was to compare the effect of monitored exercise programs differing in daily frequency and exercise bout duration on aerobic fitness and weight loss during a period of caloric restriction. It was hypothesized that multiple, short exercise bouts performed daily would result in similar cardiovascular improvements and weight loss compared to one long bout performed daily.
| MATERIALS AND METHODS |
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28 kg/m2 at baseline. Participants were excluded from the study if they were currently taking any medication or if there were other medical problems that could influence heart rate and/or exercise capacity. Subjects did not participate in regular, structured exercise, and were weight stable with no significant weight loss or gain at least six months prior to the study. Following initial screening, subjects signed an informed consent describing the nature of the investigation. The study was conducted in accordance with and approval by the universitys Institutional Review Board for Human Subjects.
Study Design
Participants reported to the lab wearing shorts and a t-shirt and underwent assessments at baseline and following 12 weeks of aerobic exercise training. Height and weight were measured (shoes off) using a balance beam scale. Skinfold thickness was measured using Lange skinfold calipers (Beta Technology, Inc., Cambridge, MD) at seven sites (chest, triceps, subscapular, suprailliac, abdomen, axilla and mid-thigh) and circumference was assessed using a tape measure at the hip, waist, thigh, and upper arm. All skinfold and circumference measures were performed by an experienced tester who was otherwise not involved with the study. Cardiovascular fitness was determined using the Astrand maximal cycle test protocol [14]. Oxygen uptake was measured continuously (breath by breath) with a Medgraphics CPX/D series cardiopulmonary exercise testing system (MedGraphics, St Paul, MN). The criteria for attainment of VO2 max included a respiratory exchange ratio of
1.10 and a peak heart rate within 10 beats/min of age predicted maximal heart rate. Resting energy expenditure (REE) was measured (baseline only) on a separate day during early morning hours with subjects in a 12 hour fasted state. The test procedure for REE measurement required the subject to rest quietly in the lab for a period of 15 minutes prior to measurement. Seated upright in a chair, a mouthpiece and noseclip were placed on the subject and oxygen uptake was monitored for a period that varied from 512 minutes, depending on how quickly five consecutive steady state oxygen uptake readings were recorded by the metabolic cart. REE was measured using a MedGraphics CPX Express System (MedGraphics, St Paul, MN). Prior to each test, the flowmeter was calibrated with multiple comparisons to a 3-liter syringe while O2 and CO2 analyzers were calibrated automatically by the metabolic cart software following the presentation of high- and low-span gases. This procedure was in accordance with system requirements.
Intervention
Following baseline testing, subjects were assigned (non-random) to one of four groups based on class schedules and availability: a nonexercising control group (control), a 30 minutes daily continuous exercise group with one bout lasting 30 minutes (1 x 30), a 30 minutes daily accumulated exercise group with two bouts, each lasting 15 minutes (2 x 15), and a second 30 minutes daily accumulated exercise group with three bouts, each lasting 10 minutes (3 x 10). Subjects assigned to the control group were asked to maintain their normal activity routine throughout the study. Those subjects assigned to the exercise groups completed 12 weeks of aerobic exercise training at 75% of their heart rate reserve (HRR), ± 5 beats per minute using the Karvonen, Ketala, and Mustala [15] formula, three to five days per week. Each exercising subject was asked to monitor their own resting heart rate with measurement taking place each morning, before getting out of bed. Based on possible training adaptations and subsequent changes in resting heart rate, training intensity was re-calculated weekly. The Schwinn AirDyne (Schwinn Cycling and Fitness, Inc., Boulder, CO) was chosen as the form of exercise when pilot testing and pre-test screening indicated that it required minimal learning time and was a preferred activity compared to treadmill walking and/or a cross country skiing device. Subjects reported to the designated exercise room of the physical education building during scheduled hours where a trained undergraduate student exercise leader was responsible for recording attendance and exercise heart rates. The exercise protocols (Table 1) were designed such that for weeks 12, total exercise duration was 15 minutes per day, 20 minutes per day for weeks 34, and 30 minutes per day for weeks 512.
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Subjects were instructed to follow a self-monitored, calorie-restricted diet (total calorie intake = 80% of REE). Attendance at two classroom sessions was required where sample menus, accurate serving sizes and food caloric values were provided. Three day food records were completed at baseline (prior to REE measurement), mid-study (6 weeks), and during the final week of exercise (12 weeks). Dietary data were collected using The Food Processor, Version 7.3 (ESHA Research, Salem, OR).
In an effort to account for physical activity beyond the prescribed exercise programs, each subject was issued a Silva electronic pedometer (Binghamton, NY). Subjects were asked to wear the pedometer for the duration of the study during all waking hours when they were not involved in the study-related exercise sessions and the number of miles accumulated was recorded weekly.
Statistics
Data analysis was performed using SYSTAT 9.0S (SPSS Inc., Chicago, IL). A one way analysis of variance (ANOVA) was used to determine possible baseline differences between groups and a 4 x 2 (group by time) repeated measures ANOVA was employed to analyze the pre- and post-treatment data for aerobic fitness, weight, body mass index, and the sum of skinfolds/circumferences. The repeated measures ANOVA was also used to compare total calorie intake, physical activity beyond the structured exercise program, and exercise participation between groups across the twelve weeks of the study. Tukey post hoc analyses were used to indicate significant response differences where an interaction was observed. A Chi Square test of the percentage of subjects who dropped out of the three exercising groups was also performed. Delta scores (baseline and post-treatment values) were calculated on selected variables and analyzed using a one way ANOVA. The statistical significance level of p
0.05 was chosen and all values are expressed as means plus or minus the standard deviation of the mean (X ± SD).
| RESULTS |
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The results of the pedometer data revealed no significant difference (F(3,34) = 1.81, p < 0.16) between groups with regard to miles accumulated per week (control = 13.5 ± 4.5; 1 x 30 = 12.8 ± 4.5; 2 x 15 = 13.2 ± 2.6; 3 x 10 = 16.5 ± 2.7). The total number of days that subjects exercised was averaged for each three week period and a significant main effect of time (F(3,81) = 36.2, p < 0.0001) was observed as the three exercise groups showed steadily declining attendance from the beginning to the end of the twelve week training period (Fig. 2). Exercise participation did not differ significantly among the exercise groups with regard to the average number of days per week they attended the sessions (1 x 30 = 3.9 ± 0.51; 2 x 15 = 3.7 ± 0.46; 3 x 10 = 3.7 ± 0.56). A Chi Square test of the percentage of subjects who dropped out of the three exercising groups showed statistical significance (X2 = 28.7, p < 0.0001) as the 1 x 30 group had 0% dropout compared to 17% for the 2 x 15 group and 33% for the 3 x 10 group.
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| DISCUSSION |
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The major finding of this study supports previous research whereby accumulated exercise (i.e., 2 x 15, 3 x 10) resulted in similar benefits when compared to one 30 minute bout of exercise per day (1 x 30). Aerobic fitness, assessed directly, improved in all three exercise groups, consistent with what similar studies that measured VO2 max directly and used self-reported exercise have shown. DeBusk, Stenestrand, Sheehan, and Haskell [6], studied sedentary, middle aged men who were randomly allocated to either a 30 minute jogging session or three 10 minute jogging sessions, five days per week for a period of eight weeks. The authors reported similar decreases in body mass for both groups with a significantly greater increase in VO2 max for the long bout group. The multiple exercisers responded with a 7.6% VO2 max increase (2.4 mL/kg/min). Jakicic, Wing, Butler, and Robinson [7] found that thirty or forty minutes of intermittent aerobic exercise was more effective for maintaining exercise adherence and just as effective for improving cardiovascular endurance and weight loss in overweight women when compared to thirty or forty minutes of continuous aerobic exercise. Murphy and Hardman [8] showed similar fitness improvements (8% increase in VO2 max, 2.5 mL/kg/min) and decreased body fat with multiple, short bouts of brisk walking when compared to longer walking bouts of the same total duration in sedentary middle aged women. Woolf-May et al. [9] reported significantly reduced step test heart rates (suggesting improved aerobic fitness) following an 18 week walking program in previously sedentary subjects who completed walks of 1015 minutes, up to three times per day. In an 18 month intervention trial by Jakicic, Winters, Lang, and Wing [10], subjects exercising in short bouts (i.e., two to four exercise bouts per day for 10 minutes each) were compared to an identical short bout group that was provided with home treadmills and a third group of long bout (2040 minutes continuous) exercisers. VO2 max increased significantly in all three groups while long term weight loss maintenance was enhanced in the short bout, home treadmill group. One study investigating obese women who walked briskly for 10 minutes three times per day for 32 weeks resulted in no significant change in VO2 max or body mass [11] yet 7 of 13 subjects did show improvement in both parameters. Boreham, Wallace, and Neville [12] have also shown that cardiovascular health benefits (i.e, increased HDL cholesterol and reduced total:HDL ratio) can be derived by females performing a seven week stair climbing program.
The disparity in percentage of VO2 max increase between previous research and this study may be explained by the differing baseline VO2 max values of the subjects which were quite low in our subjects (<10th percentile). Furthermore, in the present investigation, subjects in the exercising groups were instructed to exercise at 75% of their heart rate reserve with a range of plus or minus five beats per minute. The use of heart rate monitors and exercise leaders further ensured that all subjects maintained their target heart rates and completed the required amount of exercise for each session. If, as suggested by Jakicic, Polley and Wing [13], subjects over-reported the amount of exercise they actually performed in the previous work cited, this would provide a valid explanation for the greater increase in VO2 max observed in the present investigation. Examination of the actual values recorded shows that the magnitude (i.e., L/min) of aerobic capacity increase in the exercising groups is actually quite similar to that of the walkers in the Murphy and Hardman [8] paper.
The exercising subjects in this investigation showed significant decreases in body weight, body mass index (kg/m2), sum of skinfolds and sum of circumference measures from baseline to post-treatment while the values for the nonexercising control subjects actually increased slightly over the same time frame. Jakicic, Wing, Butler, and Robertson [7] reported a greater magnitude of decrease for these parameters, especially for short bout exercisers. This is perhaps best explained by the longer duration (20 weeks) of their treatment and what appears to be a more rigorous dietary intervention with weekly behavioral sessions. Furthermore, a potential problem with our use of the 80% REE method of caloric restriction is that menstrual cycle status was not controlled and this has been shown to influence REE to some extent [16]. The actual amount of weight lost by the exercising subjects in this study could certainly be considered modest; however, the pre- to post-treatment delta scores for sum of skinfolds and circumferences do indicate similar, positive changes in body composition for all three groups.
The fact that the control subjects in our study did not lose weight is perplexing and conflicts with other research that generally supports weight loss with caloric restriction [17, 18]. One explanation may be that subjects simply underreported the amount of calories consumed, thus making this an issue of noncompliance. Furthermore, it would seem plausible that subjects may have adhered to the calorie restricted diet for the initial six weeks and, following the mid-study (six week) dietary assessment, returned to their pre-study eating habits. This could also explain the relatively small amount of weight lost by the exercising subjects as well, despite the significant calorie deficit they would have likely incurred with an increase in exercise induced energy expenditure.
While not the primary focus of this study, the data regarding exercise participation are intriguing. Blair et al. [19] have suggested that by performing multiple, shorter bouts of exercise over the course of a day, exercise could be made more convenient to the average American and exercise adherence could be enhanced. In the present investigation, there was no difference between the exercising groups in the number of days subjects exercised, although there was a significant decline in daily attendance for all three groups from the first three weeks to the final six weeks of the exercise intervention. Furthermore, there were subjects who dropped out of the multiple, short bout groups initially (first week) due to scheduling difficulties that, according to these subjects, were directly related to the requirement of two or three bouts per day. The 2 x 15 and 3 x 10 subjects that performed their earlier exercise session(s), with the exception of only four instances, faithfully returned later in the day for their second and/or third session. Of further interest was that subjects in these groups were often likely to miss their later exercise session if they had already missed their first. Therefore, when calculating the total minutes spent exercising, the results were nearly identical to those comparing the total number of days spent exercising. Unfortunately, interpretation of the data with regard to participation or exercise adherence is problematic due to the fact that subjects were not randomly assigned to groups, an obvious limitation of our study. This was due primarily to the logistical problems presented by our rigorous exercise protocol, specifically the requirement that all exercise sessions had to be monitored and performed in a facility separate from subjects living quarters.
In conclusion, based on the results of this study it appears that two or three short bouts of exercise have the same effect as one continuous bout of exercise with regard to aerobic fitness and weight loss in overweight college aged women. To the best of our knowledge, this is the first published study comparing multiple, short bouts of exercise to continuous exercise where all exercise bouts were monitored, timed, and recorded by trained exercise personnel. While self reported exercise behavior studies provide important and practical information, verification of the frequency, intensity and actual time spent exercising are equally critical to our further understanding of this research question.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Received March 30, 2001. Accepted July 27, 2001.
| REFERENCES |
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