Journal of Physical Activity and Health, 2015, 12, 764 -769 http://dx.doi.org/10.1123/jpah.2013-0441 © 2015 Human Kinetics, Inc.
ORIGINAL RESEARCH
Examining the Relationship Between Physical Activity Intensity and Adiposity in Young Women Bruce W. Bailey, Pamela Borup, James D. LeCheminant, Larry A. Tucker, and Jacob Bromley Background: The purpose of this study was to assess the relationship between intensity of physical activity (PA) and body composition in 343 young women. Methods: Physical activity was objectively measured using accelerometers worn for 7 days in women 17 to 25 years. Body composition was assessed using the BOD POD. Results: Young women who spent less than 30 minutes a week performing vigorous PA had significantly higher body fat percentages than women who performed more than 30 minutes of vigorous PA per week (F = 4.54, P = .0113). Young women who spent less than 30 minutes per day in moderate to vigorous PA (MVPA) had significantly higher body fat percentages than those who obtained more than 30 minutes per day of MVPA (F = 7.47, P = .0066). Accumulating more than 90 minutes of MVPA per day was associated with the lowest percent body fat. For every 10 minutes spent in MVPA per day, the odds of having a body fat percentage above 32% decreased by 29% (P = .0002). Conclusion: Vigorous PA and MVPA are associated with lower adiposity. Young women should be encouraged to accumulate at least 30 minutes of MVPA per day, however getting more than 90 minutes a day is predictive of even lower levels of adiposity. Keywords: body composition, exercise, obesity, health behavior, guidelines and recommendations
Preventing obesity and its associated health risks is increasingly salient to public health.1–3 To prevent the development of obesity it is important to intervene during periods where excess weight tends to be gained or unhealthy habits established. One of these critical periods for the development of obesity is during late adolescence and early adulthood.4,5 Specifically, the college years are a critical time in which to prevent excess weight gain. It has been shown that physical activity tends to decline in the transition from high school to college.6 Though not always a straightforward relationship, physical activity has been associated with body fat during the college years.7–10 However, studies using objective measures of physical activity in women during late adolescence and early adulthood are scarce.11 All but 1 of the studies evaluating the relationship between physical activity and adiposity used subjective measures of physical activity, and the intensity of activity has not been well evaluated. In fact, the role of physical activity intensity in weight management continues to be debated. To date, the 1 study in young women that used accelerometers to evaluate the relationship between adiposity and physical activity was limited by sample size and was able to only evaluate simple relationships.8 Current physical activity recommendations for weight management focus primarily on duration within a wide intensity range termed moderate to vigorous activity (MVPA).12 There is no doubt that more time in MVPA leads to greater energy expenditure and is related to lower body weight. However, the intensity of physical activity and duration that is optimal for body weight in young women has not been evaluated. In addition, most studies have used body mass index (BMI) to classify adiposity. While BMI is easy to measure, it is also limited, especially in studies of physical activity. This is because higher levels of physical activity tend to result in greater lean body mass as well as lower body fat.13–15 This change The authors are with the Dept of Exercise Sciences, Brigham Young University, Provo, UT. Bailey ([email protected]) is corresponding author. 764
in body composition cannot be detected using BMI, which is based on only height and weight. A better understanding of the relationship between intensity of physical activity and body composition can aid in preventing excess weight gain during college. The purpose of this study was to identify associations between physical activity levels and body composition among young adult women, with specific emphasis on intensity and time spent in light, moderate, and vigorous activity. A secondary purpose was to evaluate the impact of potential confounding factors, such as energy intake, age, and season of assessment, on these relationships.
Methods and Procedures Design This study was cross-sectional. Three hundred and seventy women were recruited to participate. Data were collected beginning in the fall of 2009 and continued through the fall of 2012.
Participants Participants included women ages 17 to 25 years. To join the study, participants had to be free from any health condition that would limit physical activity or affect metabolism. Thus, participants were able to participate in moderate to vigorous activity without limitations. Participants were nonsmokers. Those who gave birth in the past 6 months or were pregnant were excluded from the study. Women taking any medications that alter metabolism were also excluded from the study. The most common medications that excluded participation were thyroid hormone, medications for depression, and medications related to anxiety. Recruitment for the study was done using posters, flyers, a Facebook group, and word of mouth. Those interested in participating filled out a screening form to ensure the inclusion criteria were met. Before participating in the assessment, all participants signed
Intensity of Activity and Adiposity 765
an informed consent form approved by the university’s Institutional Review Board.
Downloaded by University of California on 09/21/16, Volume 12, Article Number 6
Procedures Participants who met the inclusion criteria were asked to participate in 2 laboratory appointments separated by 7 full days. At the first assessment height and weight were measured and body composition was assessed using the BOD POD (Life Measurement, Inc., Concord, CA). Participants were given a belt with the ActiGraph GT3X accelerometer (ActiGraph, Pensacola, FL) attached and instructed on how to properly wear the belt. A physical activity form was sent home with the participants on which they logged exercise activities performed, any times the belt was removed, and the activities performed while the belt was off (eg, swimming). During the 7 days of activity monitoring each participant was contacted by phone to ensure she was properly wearing the activity monitor. Following the 7 days of activity monitoring participants came in for the second laboratory appointment. At this point participants returned the activity monitor, activity monitor data were downloaded and checked to make sure that the data files were complete. If the participant forgot to wear the monitor or the data were unusable (as a result of a monitor malfunction) the participant was asked to wear the monitor again. Following completion of the study, participants were given their body composition results and received a $15 cash incentive for participating.
Instrumentation and Measurement Methods Body Weight and Height. Body weight was measured using a
digital scale (Tanita Corporation, Japan; modified by Life Measurement, Inc., Concord, CA) accurate to the nearest 0.005 kg. To standardize the assessment, participants were weighed while wearing a standard 1-piece swimsuit. The scale was calibrated every 2 weeks. Height was measured without shoes and using a wall-mounted stadiometer (Seca, Chino, CA) and recorded to the nearest 0.1 cm. Body mass index was calculated by dividing a participant’s mass in kilograms by her height in meters squared.
Body Composition. Waist and hip circumferences were mea-
sured in triplicate and the average of 3 measurements was used for analysis. Using a spring loaded Gulick measuring tape (Fitness Wholesale, Stow, OH), waist circumference was assessed at the narrowest portion of the abdomen and hip circumference was assessed at the widest portion of the buttocks. The BOD POD was used to determine body fat percentage. The BOD POD has been shown to produce reliable and valid measurements of body composition in comparison with dual energy x-ray absorptiometry (DEXA).16 The reliability has been rated at good to excellent.17 Within-subject coefficients of variation for percent body fat have ranged from 1.7% to 4.5% within a day and from 2.0% to 2.3% between days (P ≤ .05).17,18 Thoracic volume was measured twice to make sure readings were within 0.300 ml of each other. The average of the 2 readings was used to calculate body fat percentage.
Physical Activity. The ActiGraph GT3X accelerometer was used
to objectively measure physical activity. Accelerometers have shown good correlations (r = .74–.95) to energy expenditure during walking, running, and other defined activities.19–21 The accelerometer was worn on the right side of the body at the level of the umbilicus and above the anterior superior iliac spine. Participants wore the accelerometer continually for 7 consecutive days, removing it for
water activities only. Participants were given an activity log and were asked to record their exercise as well as any times the accelerometer had to be removed for water activities. A day’s data were considered complete if the participant wore the monitor 75% of the time between 7 AM to 11 PM Nonwear time was conservatively defined as 20 or more minutes of consecutive zeros.22 Data were collected in 60 second epochs. Physical activity intensity levels were categorized using the following cut-points: vigorous activity (> 5999 counts/min), moderate activity (2020–5999 counts/min), light activity (250–2019 counts/min), and sedentary (0–249 counts/min).23,24
Data Analysis The purpose of this study was to assess the relationship between physical activity intensity and body composition. The criterion variable was body fat percentage and the predictor variable was intensity of physical activity. Descriptive statistics (mean, standard deviation, etc.) were reported for all variables of interest. All variables were checked for normality. Since vigorous activity was not normally distributed it was log transformed for linear data analysis. Pearson product-moment correlations were used to measure bivariate relationships. For data analysis of both moderate to vigorous activity and just vigorous activity, participants were divided into groups. For moderate to vigorous activity, groups were created for every 30 minutes per day of moderate to vigorous activity. This increment of time was chosen because it represents a common daily recommendation of physical activity.25,26 For time spent in vigorous activity, groups were created for those who participate in 0 to 29, 30 to 74, and ≥ 75 minutes per week of vigorous activity. Seventy-five minutes was selected because it is the current weekly recommendation for vigorous activity and 30 minutes was selected because it is between 0 and 75 minutes and is a common amount of time to participate in vigorous activity.27 The general linear model was used to detect differences between groups for variables of interest. The best predictors for outcomes of interest were identified through stepwise regression. Logistic regression was used to assess the probability of having excess body fat (≥ 32%) given the amount of time spent in MVPA per day.28 Appropriate controls (age and season of assessment) were added to the statistical models to account for potentially confounding variables. Seasons were developed by grouping 3 months with similar temperatures together into winter, spring, summer, and fall seasons. The SAS system 9.3 (Cary, NC) was used to compute all statistical analyses. The level of significance was set at 0.05.
Results A total of 370 women were recruited to participate in the study. Of those 370 women, 351 met inclusion criteria and 343 had complete body composition and activity data. All women included in the analysis had at least 2 complete weekend days and 3 complete weekdays of physical activity observation. The mean number of days observed was 6.7 ± 0.7 and wear time was excellent with a mean of 13.1 ± 3.4 hours per day between the hours of 8 AM and 11 PM. The characteristics of the 343 women are reported in Table 1. Participants were primarily Caucasian (88.2%), with the remaining women including Asian, Hispanic, African-American, and other. The mean age of participants was 20.2 ± 1.6 years and the average time spent in moderate to vigorous activity was 62.9 ± 23.1 minutes. Using BMI, 4% of the women were underweight (< 18.5 kg m-2),
JPAH Vol. 12, No. 6, 2015
766 Bailey et al
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79% were normal weight (18.5–24.9 kg m-2), 14% were overweight (25–29.9 kg m-2), and 3% were obese (≥ 30 kg m-2). While only 3% of the women were obese by BMI, 18% of the women had a body fat level classified as “obese” (≥ 32%).28 The top 4 reported activities among participants were jogging, sports, dancing, and weight lifting. Stepwise regression indicated that the best predictor of body fat was the log-transformed time spent in vigorous physical activity per day (F = 14.32, P = .0002). Moderate activity was also related to percent body fat (F = 6.10, P = .0140), while light activity was not. When women were divided into groups based on time spent in vigorous physical activity (0–29 min/week, 30–74 min/week, and > 75 min/week), young women who engaged in less than 30 minutes of vigorous activity per week had higher percent body fat than women who spent 30 minutes or longer in vigorous activity per
week (F = 4.54, P < .0113) (Table 2). Controlling for age, season, and energy intake had a statistically negligible impact on the relationship. However, controlling for total activity counts weakened the relationship by 71.3% and the difference between vigorous activity groups was no longer significant. When participants were divided into groups based on time spent in MVPA (0–29 min/day, 30–59 min/day, 60–89 min/day, and ≥ 90 min/day), body fat differed significantly across groups (F = 7.47, P = .0002) (Table 3). Those women in the group which spent less than 30 minutes per day in MVPA had significantly higher body fat percentages than those women who obtained more than 30 minutes per day. In addition, those women who engaged in more than 90 minutes of MVPA per day had a body fat that was lower than women who engaged in less than 60 minutes per day. When controlling for age, energy intake, and season, the relationship was weakened by 29.7% but remained significant (F = 4.67, P = .0033). Differences in body fat were examined according to time spent at varying intensity levels (Table 4). For activity in the lower end of moderate intensity (~4 METS or lower), percent body fat decreased as duration increased. For activity at the higher end of moderate intensity and vigorous intensity (~4.9 METS or greater), there was no apparent benefit of accumulating more than 30 minutes per week. However, those who accumulated less than 30 minutes per week at any intensity level had significantly higher body fat. Logistic regression revealed that for every 10 minutes spent in MVPA per day, the odds of being obese (≥ 32% body fat) decreased by 29% (Figure 1). The probability of being obese for a woman who obtained only 10 minutes per day of MVPA was 0.46, whereas the probability for a woman who obtained 120 minutes was 0.04. Odds ratios revealed that the odds of being obese by body fat for those who did not obtain at least 30 minutes per day of MVPA was 5.3 (95% CI: 2.0–14.0) times greater than those who obtained 30 minutes or more per day. The odds of being obese by body fat was 10.1 times (95% CI: 1.4–74.8) higher for those who did not get 90 minutes of MVPA per day compared with those who got more than 90 minutes a day.
Table 1 Descriptive Data for All Participants (n = 343) Variable
Mean
SD
Range
Age
20.2
1.6
17.7–26.1
Height (cm)
166.1
6.8
147.2–183.6
Weight (kg)
62.3
9.3
42.9–96.2
22.5
2.9
17.1–34.8
26.6
6.2
10.3–44
393.4
127.0
138.8–1059.8
Light activity (min/day)
169.2
44.3
83.1–337.3
Moderate activity (min/day)
55.7
19.6
6.0–136.3
BMIa
(kg·m-2)
Body fat (%) Activity
counts/daya
Vigorous activity (min/day)
6.2
9.0
0–65.3
MVPAc (min/day)
62.9
23.1
6–178.8
a Counts
divided by 1000 Abbreviations: BMI, body mass index; MVPA, moderate-to-vigorous physical activity.
Table 2 Time Spent in Vigorous Activity and the Relationship to Adiposity and Time Spent in Other Physical Activity Intensities Group 1
Group 2
Group 3
0–29 min/week
30-74 min/week
≥75 min/week
n = 188
n = 55
n = 65
Mean
SD
Mean
SD
Mean
SD
F
P
Body fat (%)
27.4a
6.4
25.7b
5.3
25.5b
5.1
4.54
ORIGINAL RESEARCH
Examining the Relationship Between Physical Activity Intensity and Adiposity in Young Women Bruce W. Bailey, Pamela Borup, James D. LeCheminant, Larry A. Tucker, and Jacob Bromley Background: The purpose of this study was to assess the relationship between intensity of physical activity (PA) and body composition in 343 young women. Methods: Physical activity was objectively measured using accelerometers worn for 7 days in women 17 to 25 years. Body composition was assessed using the BOD POD. Results: Young women who spent less than 30 minutes a week performing vigorous PA had significantly higher body fat percentages than women who performed more than 30 minutes of vigorous PA per week (F = 4.54, P = .0113). Young women who spent less than 30 minutes per day in moderate to vigorous PA (MVPA) had significantly higher body fat percentages than those who obtained more than 30 minutes per day of MVPA (F = 7.47, P = .0066). Accumulating more than 90 minutes of MVPA per day was associated with the lowest percent body fat. For every 10 minutes spent in MVPA per day, the odds of having a body fat percentage above 32% decreased by 29% (P = .0002). Conclusion: Vigorous PA and MVPA are associated with lower adiposity. Young women should be encouraged to accumulate at least 30 minutes of MVPA per day, however getting more than 90 minutes a day is predictive of even lower levels of adiposity. Keywords: body composition, exercise, obesity, health behavior, guidelines and recommendations
Preventing obesity and its associated health risks is increasingly salient to public health.1–3 To prevent the development of obesity it is important to intervene during periods where excess weight tends to be gained or unhealthy habits established. One of these critical periods for the development of obesity is during late adolescence and early adulthood.4,5 Specifically, the college years are a critical time in which to prevent excess weight gain. It has been shown that physical activity tends to decline in the transition from high school to college.6 Though not always a straightforward relationship, physical activity has been associated with body fat during the college years.7–10 However, studies using objective measures of physical activity in women during late adolescence and early adulthood are scarce.11 All but 1 of the studies evaluating the relationship between physical activity and adiposity used subjective measures of physical activity, and the intensity of activity has not been well evaluated. In fact, the role of physical activity intensity in weight management continues to be debated. To date, the 1 study in young women that used accelerometers to evaluate the relationship between adiposity and physical activity was limited by sample size and was able to only evaluate simple relationships.8 Current physical activity recommendations for weight management focus primarily on duration within a wide intensity range termed moderate to vigorous activity (MVPA).12 There is no doubt that more time in MVPA leads to greater energy expenditure and is related to lower body weight. However, the intensity of physical activity and duration that is optimal for body weight in young women has not been evaluated. In addition, most studies have used body mass index (BMI) to classify adiposity. While BMI is easy to measure, it is also limited, especially in studies of physical activity. This is because higher levels of physical activity tend to result in greater lean body mass as well as lower body fat.13–15 This change The authors are with the Dept of Exercise Sciences, Brigham Young University, Provo, UT. Bailey ([email protected]) is corresponding author. 764
in body composition cannot be detected using BMI, which is based on only height and weight. A better understanding of the relationship between intensity of physical activity and body composition can aid in preventing excess weight gain during college. The purpose of this study was to identify associations between physical activity levels and body composition among young adult women, with specific emphasis on intensity and time spent in light, moderate, and vigorous activity. A secondary purpose was to evaluate the impact of potential confounding factors, such as energy intake, age, and season of assessment, on these relationships.
Methods and Procedures Design This study was cross-sectional. Three hundred and seventy women were recruited to participate. Data were collected beginning in the fall of 2009 and continued through the fall of 2012.
Participants Participants included women ages 17 to 25 years. To join the study, participants had to be free from any health condition that would limit physical activity or affect metabolism. Thus, participants were able to participate in moderate to vigorous activity without limitations. Participants were nonsmokers. Those who gave birth in the past 6 months or were pregnant were excluded from the study. Women taking any medications that alter metabolism were also excluded from the study. The most common medications that excluded participation were thyroid hormone, medications for depression, and medications related to anxiety. Recruitment for the study was done using posters, flyers, a Facebook group, and word of mouth. Those interested in participating filled out a screening form to ensure the inclusion criteria were met. Before participating in the assessment, all participants signed
Intensity of Activity and Adiposity 765
an informed consent form approved by the university’s Institutional Review Board.
Downloaded by University of California on 09/21/16, Volume 12, Article Number 6
Procedures Participants who met the inclusion criteria were asked to participate in 2 laboratory appointments separated by 7 full days. At the first assessment height and weight were measured and body composition was assessed using the BOD POD (Life Measurement, Inc., Concord, CA). Participants were given a belt with the ActiGraph GT3X accelerometer (ActiGraph, Pensacola, FL) attached and instructed on how to properly wear the belt. A physical activity form was sent home with the participants on which they logged exercise activities performed, any times the belt was removed, and the activities performed while the belt was off (eg, swimming). During the 7 days of activity monitoring each participant was contacted by phone to ensure she was properly wearing the activity monitor. Following the 7 days of activity monitoring participants came in for the second laboratory appointment. At this point participants returned the activity monitor, activity monitor data were downloaded and checked to make sure that the data files were complete. If the participant forgot to wear the monitor or the data were unusable (as a result of a monitor malfunction) the participant was asked to wear the monitor again. Following completion of the study, participants were given their body composition results and received a $15 cash incentive for participating.
Instrumentation and Measurement Methods Body Weight and Height. Body weight was measured using a
digital scale (Tanita Corporation, Japan; modified by Life Measurement, Inc., Concord, CA) accurate to the nearest 0.005 kg. To standardize the assessment, participants were weighed while wearing a standard 1-piece swimsuit. The scale was calibrated every 2 weeks. Height was measured without shoes and using a wall-mounted stadiometer (Seca, Chino, CA) and recorded to the nearest 0.1 cm. Body mass index was calculated by dividing a participant’s mass in kilograms by her height in meters squared.
Body Composition. Waist and hip circumferences were mea-
sured in triplicate and the average of 3 measurements was used for analysis. Using a spring loaded Gulick measuring tape (Fitness Wholesale, Stow, OH), waist circumference was assessed at the narrowest portion of the abdomen and hip circumference was assessed at the widest portion of the buttocks. The BOD POD was used to determine body fat percentage. The BOD POD has been shown to produce reliable and valid measurements of body composition in comparison with dual energy x-ray absorptiometry (DEXA).16 The reliability has been rated at good to excellent.17 Within-subject coefficients of variation for percent body fat have ranged from 1.7% to 4.5% within a day and from 2.0% to 2.3% between days (P ≤ .05).17,18 Thoracic volume was measured twice to make sure readings were within 0.300 ml of each other. The average of the 2 readings was used to calculate body fat percentage.
Physical Activity. The ActiGraph GT3X accelerometer was used
to objectively measure physical activity. Accelerometers have shown good correlations (r = .74–.95) to energy expenditure during walking, running, and other defined activities.19–21 The accelerometer was worn on the right side of the body at the level of the umbilicus and above the anterior superior iliac spine. Participants wore the accelerometer continually for 7 consecutive days, removing it for
water activities only. Participants were given an activity log and were asked to record their exercise as well as any times the accelerometer had to be removed for water activities. A day’s data were considered complete if the participant wore the monitor 75% of the time between 7 AM to 11 PM Nonwear time was conservatively defined as 20 or more minutes of consecutive zeros.22 Data were collected in 60 second epochs. Physical activity intensity levels were categorized using the following cut-points: vigorous activity (> 5999 counts/min), moderate activity (2020–5999 counts/min), light activity (250–2019 counts/min), and sedentary (0–249 counts/min).23,24
Data Analysis The purpose of this study was to assess the relationship between physical activity intensity and body composition. The criterion variable was body fat percentage and the predictor variable was intensity of physical activity. Descriptive statistics (mean, standard deviation, etc.) were reported for all variables of interest. All variables were checked for normality. Since vigorous activity was not normally distributed it was log transformed for linear data analysis. Pearson product-moment correlations were used to measure bivariate relationships. For data analysis of both moderate to vigorous activity and just vigorous activity, participants were divided into groups. For moderate to vigorous activity, groups were created for every 30 minutes per day of moderate to vigorous activity. This increment of time was chosen because it represents a common daily recommendation of physical activity.25,26 For time spent in vigorous activity, groups were created for those who participate in 0 to 29, 30 to 74, and ≥ 75 minutes per week of vigorous activity. Seventy-five minutes was selected because it is the current weekly recommendation for vigorous activity and 30 minutes was selected because it is between 0 and 75 minutes and is a common amount of time to participate in vigorous activity.27 The general linear model was used to detect differences between groups for variables of interest. The best predictors for outcomes of interest were identified through stepwise regression. Logistic regression was used to assess the probability of having excess body fat (≥ 32%) given the amount of time spent in MVPA per day.28 Appropriate controls (age and season of assessment) were added to the statistical models to account for potentially confounding variables. Seasons were developed by grouping 3 months with similar temperatures together into winter, spring, summer, and fall seasons. The SAS system 9.3 (Cary, NC) was used to compute all statistical analyses. The level of significance was set at 0.05.
Results A total of 370 women were recruited to participate in the study. Of those 370 women, 351 met inclusion criteria and 343 had complete body composition and activity data. All women included in the analysis had at least 2 complete weekend days and 3 complete weekdays of physical activity observation. The mean number of days observed was 6.7 ± 0.7 and wear time was excellent with a mean of 13.1 ± 3.4 hours per day between the hours of 8 AM and 11 PM. The characteristics of the 343 women are reported in Table 1. Participants were primarily Caucasian (88.2%), with the remaining women including Asian, Hispanic, African-American, and other. The mean age of participants was 20.2 ± 1.6 years and the average time spent in moderate to vigorous activity was 62.9 ± 23.1 minutes. Using BMI, 4% of the women were underweight (< 18.5 kg m-2),
JPAH Vol. 12, No. 6, 2015
766 Bailey et al
Downloaded by University of California on 09/21/16, Volume 12, Article Number 6
79% were normal weight (18.5–24.9 kg m-2), 14% were overweight (25–29.9 kg m-2), and 3% were obese (≥ 30 kg m-2). While only 3% of the women were obese by BMI, 18% of the women had a body fat level classified as “obese” (≥ 32%).28 The top 4 reported activities among participants were jogging, sports, dancing, and weight lifting. Stepwise regression indicated that the best predictor of body fat was the log-transformed time spent in vigorous physical activity per day (F = 14.32, P = .0002). Moderate activity was also related to percent body fat (F = 6.10, P = .0140), while light activity was not. When women were divided into groups based on time spent in vigorous physical activity (0–29 min/week, 30–74 min/week, and > 75 min/week), young women who engaged in less than 30 minutes of vigorous activity per week had higher percent body fat than women who spent 30 minutes or longer in vigorous activity per
week (F = 4.54, P < .0113) (Table 2). Controlling for age, season, and energy intake had a statistically negligible impact on the relationship. However, controlling for total activity counts weakened the relationship by 71.3% and the difference between vigorous activity groups was no longer significant. When participants were divided into groups based on time spent in MVPA (0–29 min/day, 30–59 min/day, 60–89 min/day, and ≥ 90 min/day), body fat differed significantly across groups (F = 7.47, P = .0002) (Table 3). Those women in the group which spent less than 30 minutes per day in MVPA had significantly higher body fat percentages than those women who obtained more than 30 minutes per day. In addition, those women who engaged in more than 90 minutes of MVPA per day had a body fat that was lower than women who engaged in less than 60 minutes per day. When controlling for age, energy intake, and season, the relationship was weakened by 29.7% but remained significant (F = 4.67, P = .0033). Differences in body fat were examined according to time spent at varying intensity levels (Table 4). For activity in the lower end of moderate intensity (~4 METS or lower), percent body fat decreased as duration increased. For activity at the higher end of moderate intensity and vigorous intensity (~4.9 METS or greater), there was no apparent benefit of accumulating more than 30 minutes per week. However, those who accumulated less than 30 minutes per week at any intensity level had significantly higher body fat. Logistic regression revealed that for every 10 minutes spent in MVPA per day, the odds of being obese (≥ 32% body fat) decreased by 29% (Figure 1). The probability of being obese for a woman who obtained only 10 minutes per day of MVPA was 0.46, whereas the probability for a woman who obtained 120 minutes was 0.04. Odds ratios revealed that the odds of being obese by body fat for those who did not obtain at least 30 minutes per day of MVPA was 5.3 (95% CI: 2.0–14.0) times greater than those who obtained 30 minutes or more per day. The odds of being obese by body fat was 10.1 times (95% CI: 1.4–74.8) higher for those who did not get 90 minutes of MVPA per day compared with those who got more than 90 minutes a day.
Table 1 Descriptive Data for All Participants (n = 343) Variable
Mean
SD
Range
Age
20.2
1.6
17.7–26.1
Height (cm)
166.1
6.8
147.2–183.6
Weight (kg)
62.3
9.3
42.9–96.2
22.5
2.9
17.1–34.8
26.6
6.2
10.3–44
393.4
127.0
138.8–1059.8
Light activity (min/day)
169.2
44.3
83.1–337.3
Moderate activity (min/day)
55.7
19.6
6.0–136.3
BMIa
(kg·m-2)
Body fat (%) Activity
counts/daya
Vigorous activity (min/day)
6.2
9.0
0–65.3
MVPAc (min/day)
62.9
23.1
6–178.8
a Counts
divided by 1000 Abbreviations: BMI, body mass index; MVPA, moderate-to-vigorous physical activity.
Table 2 Time Spent in Vigorous Activity and the Relationship to Adiposity and Time Spent in Other Physical Activity Intensities Group 1
Group 2
Group 3
0–29 min/week
30-74 min/week
≥75 min/week
n = 188
n = 55
n = 65
Mean
SD
Mean
SD
Mean
SD
F
P
Body fat (%)
27.4a
6.4
25.7b
5.3
25.5b
5.1
4.54
