Context A higher duration and intensity of exercise may improve long-term weight
Objective To compare the effects of different durations and intensities of exercise
on 12-month weight loss and cardiorespiratory fitness.
Design, Setting, and Participants Randomized trial conducted from January 2000 through December 2001 involving
201 sedentary women (mean [SD] age, 37.0 [5.7] years; mean [SD] body mass
index, 32.6 [4.2]) in a university-based weight control program.
Intervention Participants were randomly assigned to 1 of 4 exercise groups (vigorous
intensity/high duration; moderate intensity/high duration; moderate intensity/moderate
duration; or vigorous intensity/moderate duration) based on estimated energy
expenditure (1000 kcal/wk vs 2000 kcal/wk) and exercise intensity (moderate
vs vigorous). All women were instructed to reduce intake of energy to between
1200 and 1500 kcal/d and dietary fat to between 20% and 30% of total energy
Main Outcome Measures Body weight, cardiorespiratory fitness, and exercise participation.
Results After exclusions, 184 of 196 randomized participants completed 12 months
of treatment (94%). In intention-to-treat analysis, mean (SD) weight loss
following 12 months of treatment was statistically significant (P <.001) in all exercise groups (vigorous intensity/high duration
= 8.9 [7.3] kg; moderate intensity/high duration = 8.2 [7.6] kg; moderate
intensity/moderate duration = 6.3 [5.6] kg; vigorous intensity/moderate duration
= 7.0 [6.4] kg), with no significant difference between groups. Mean (SD)
cardiorespiratory fitness levels also increased significantly (P = .04) in all groups (vigorous intensity/high duration = 22.0% [19.9%];
moderate intensity/high duration = 14.9% [18.6%]; moderate intensity/moderate
duration = 13.5% [16.9%]; vigorous intensity/moderate duration = 18.9% [16.9%]),
with no difference between groups. Post hoc analysis revealed that percentage
weight loss at 12 months was associated with the level of physical activity
performed at 6 and 12 months. Women reporting less than 150 min/wk had a mean
(SD) weight loss of 4.7% [6.0%]; inconsistent (other) pattern of physical
activity, 7.0% [6.9%]; 150 min/wk or more, 9.5% [7.9%]; and 200 min/wk or
more of exercise, 13.6% [7.8%].
Conclusions Significant weight loss and improved cardiorespiratory fitness were
achieved through the combination of exercise and diet during 12 months, although
no differences were found based on different exercise durations and intensities
in this group of sedentary, overweight women.
An estimated 60% to 65% of adults in the United States are overweight.1 Obesity has been linked to an increase in the prevalence
of chronic diseases such as cardiovascular disease, diabetes, and cancer.2 Exercise is an important component of behavioral interventions
targeting overweight and obese adults,2 has
been shown to be important for improving short-term weight loss when combined
with changes in dietary intake,2 and is one
of the best predictors of long-term weight loss.3 However,
the optimal amount of exercise necessary to enhance long-term weight loss
has not been established, leading to differing recommendations from leading
health organizations. The Centers for Disease Control and Prevention and the
American College of Sports Medicine recommend a minimum of 30 minutes of moderate-intensity
activity on most days of the week to improve health (150 min/wk),4 whereas the Institute of Medicine recommends a minimum
of 60 min/d of exercise on most days of the week to control body weight.5
Although a recent study reported no significant difference between 30
vs 60 minutes of exercise per day on weight loss over 12 weeks,6 long-term
data from randomized clinical trials examining the effect of different durations
of exercise on weight loss are lacking. Moreover, while some evidence from
short-term studies (<6 months) shows that energy expenditure rather than
exercise intensity may have the greatest impact on body weight,7 there
are no data from long-term clinical trials to support these findings. The
purpose of this study was to examine the effect of exercise of varying duration
(moderate vs high) and intensity (moderate vs vigorous) on weight loss and
cardiorespiratory fitness following 12 months of treatment in overweight women.
A total of 201 women were randomized in this study (Figure 1). To be eligible for participation, baseline body mass
index (BMI) had to be 27 to 40, with age ranging from 21 to 45 years. In addition,
all participants were classified at baseline as sedentary, which was defined as reporting exercising less than 3 d/wk for less
than 20 min/d over the previous 6 months. Participants were excluded if they
met any of the following criteria: a history of myocardial infarction, taking
medication that would alter the heart rate response during exercise (eg, β-blockers),
taking medication that would affect metabolism or weight loss (eg, thyroid
medication), being treated for psychological conditions, currently pregnant,
pregnant within the previous 6 months, or planning to become pregnant during
the intervention period, having any medical condition that could affect metabolism
or body weight (eg, diabetes), or having a medical condition that would limit
Participants completed a detailed medical history and physical activity
readiness questionnaire prior to entry into this study and provided permission
from their personal physician indicating that the proposed intervention was
not contraindicated. All participants provided written informed consent prior
to initiating this study, and the protocol was approved by the institutional
review board of the Miriam Hospital (Providence, RI).
Behavioral Weight Loss Intervention
All participants were enrolled into a standard behavioral weight loss
intervention, which was based on social cognitive theory. The study was conducted
from January 2000 through December 2001. Participants were scheduled to attend
behavioral group meetings throughout the 12-month intervention period. Meetings
were conducted weekly during the initial 24 weeks of treatment, and biweekly
for the remainder of the study period. In addition to group meetings, participants
received a biweekly telephone call from a member of the intervention team
during months 7 through 12. These calls lasted approximately 10 minutes. All
participants also were instructed to reduce energy intake to between 1200
and 1500 kcal/d, and to reduce intake of dietary fat to between 20% and 30%
of total energy intake. Participants were provided with meal plans and were
instructed to self-monitor dietary patterns in weekly food diaries.
Participants were randomized to 1 of 4 exercise groups based on estimated
energy expenditure (1000 kcal/wk vs 2000 kcal/wk) and exercise intensity (moderate
vs vigorous). The targeted estimated energy expenditure of the exercise was
converted to minutes per week based on the differences in exercise intensity
that were prescribed. Thus, participants were randomized to (1) vigorous intensity/high
duration, (2) moderate intensity/high duration, (3) moderate intensity/moderate
duration, or (4) vigorous intensity/moderate duration (Table 1).
Participants were instructed to exercise 5 d/wk with walking encouraged
as the primary mode of exercise. Exercise intensity was prescribed both in
terms of percentage of age-predicted maximal heart rate and rating of perceived
exertion based on the Borg Scale.8 The exercise
was to occur in bouts of at least 10 minutes.9 Exercise
was not supervised on site, but motorized treadmills were provided to all
participants, which has been shown to be an effective behavioral strategy
for enhancing exercise participation.9 Participants
received no other incentives (eg, payments) for participation in this 12-month
study. Participants were instructed to record their weekly exercise in a log
that was returned to the intervention team, and feedback was provided to the
Outcomes of this study were assessed at 0, 6, and 12 months. Height
was measured with a wall-mounted stadiometer to the nearest 0.1 cm. Weight
was measured on a calibrated balance beam scale to the nearest 0.25 lb and
then converted to kilograms. Participants were weighed in undergarments while
wearing a cloth hospital gown. Body mass index was calculated as weight in
kilograms divided by the square of height in meters.
A submaximal graded exercise treadmill test was used to assess cardiorespiratory
fitness. The speed of the treadmill was constant at 80.4 m/min, with grade
beginning at 0% and progressing by 2.5% at 3-minute intervals until 85% of
age-predicted maximal heart rate (computed as 220 minus age) was achieved.
Heart rate was measured using a 12-lead electrocardiogram at 1-minute intervals
and at the point of termination. A calibrated SensorMedics Vmax metabolic
cart (Yorba Linda, Calif) was used to assess breath-by-breath oxygen consumption,
and data were averaged in 20-second intervals.
Data on exercise participation were obtained from the exercise logs
and included minutes, intensity, and type of exercise. These data were used
as a process measure to assess adoption and maintenance of the prescribed
duration and intensity of exercise.
Leisure-time physical activity was assessed using 7-day physical activity
recall and was completed using a structured interview.10 Total
duration of leisure-time physical activity classified as at least moderate
intensity was computed and used for data analysis.
The 1998 version of the food frequency questionnaire developed by Block
et al11 was used to assess energy intake. This
type of food frequency questionnaire has previously been validated.11
Power calculations were computed based on expected changes in body weight
based on a 3-factor design (intensity × duration × time), with
time as the repeated measure. We estimated moderate intraclass correlations
(0.40-0.60) among the repeated measures for the major dependent variable (body
weight). Using a conservative and moderate effect size (0.50), and taking
into consideration moderate intraclass correlations among the repeated measures
(0.40-0.60), we estimated that 40 participants per group would provide at
least 70% statistical power at an α level of .05. To allow for the potential
for a 15% to 20% attrition rate, 50 women were randomized to each treatment
Based on the study design, a priori analyses were performed to assess
differences in the outcome variables based on randomization group. Additional
analyses were performed based on post hoc grouping of participants according
to duration of reported physical activity participation.
Mixed-effects models were used to examine the significant group, time,
and group-time interaction effects for the primary outcomes. Five participants
were not followed up for the 12-month period because of pregnancy (n = 4)
and a nonstudy-related death (n = 1) and were excluded from all analyses.
Other participants with missing data for the primary outcome variables were
included in intention-to-treat analyses using baseline values carried forward.
Least-square means were obtained from the models and differences between groups
were tested with Bonferroni adjustment. Statistical analyses were performed
using SAS (version 8, SAS Institute Inc, Cary, NC). P≤.05
(2-tailed) was used to identify statistical significance.
Demographic characteristics of participants are shown in Table 2. There were no significant differences in baseline characteristics
between women randomly assigned to each of the 4 exercise groups. Excluding
the 5 participants who became pregnant or had a nonstudy-related death, 184
(94%) of 196 randomized participants completed the study. χ2 Analysis
showed no significant difference in completion rates between groups (vigorous
intensity/high duration = 96%; moderate intensity/high duration = 88%; moderate
intensity/moderate duration = 88%; vigorous intensity/moderate duration =
94%). The reasons for attrition are shown in Figure 1. There was no significant difference in baseline age, weight,
BMI, or cardiorespiratory fitness between participants who completed or dropped
out of this study (data not shown).
Attendance, Exercise, and Energy Intake
Study participants attended a mean (SD) of 79.2% (19.2%) of group sessions
for months 0 through 6, with an attendance of 71.4% (21.1%) over the entire
12-month period. The telephone intervention was implemented during months
7 through 12 and 75.1% (27.2%) of telephone calls were completed. There were
no significant differences between groups for percentage of group sessions
attended or telephone calls completed.
Exercise participation data are presented in Table 3 and are based on exercise logs for months 0 through 6 and
months 7 through 12. There was a significant exercise duration effect (P = .048), indicating that the minutes of exercise were
greater in the vigorous intensity/high duration and moderate intensity/high
duration groups compared with the moderate intensity/moderate duration and
vigorous intensity/moderate duration groups. For rating of perceived exertion,
there was a significant exercise intensity effect (P<.001
for 0-6 and 7-12 months) and exercise intensity × time (P = .04 for 0-6 months and P = .02 for 7-12
months). These results indicate that the rating of perceived exertion was
greater in the vigorous intensity/moderate duration and vigorous intensity/high
duration groups compared with the moderate intensity/moderate duration and
moderate intensity/high duration groups. Similar results were shown for heart
rate per exercise session for intensity effect (P =
.002 for 0-6 months and P<.001 for 7-12 months)
and exercise intensity × time (P = .49 for
0-6 months and P = .06 for 7-12 months) (Table 3). Walking was reported for 87.5%
of the exercise sessions (brisk walking = 30.8%; treadmill walking = 56.7%)
across the 12 months of treatment.
Data for leisure-time physical activity and energy intake are presented
in Table 3. There was no significant
difference in the pattern of change between groups for minutes of leisure-time
physical activity of at least moderate intensity, total energy intake, and
percentage of energy intake consumed as dietary fat.
Percentage weight loss data are shown in Figure 2. Additional body weight and BMI data are presented in Table 4. The mean (SD) weight loss at 12
months was 8.9 (7.3) kg for the vigorous intensity/high duration group; 8.2
(7.6) kg, moderate intensity/high duration; 6.3 (5.6) kg, moderate intensity/moderate
duration; and 7.0 (6.4) kg, vigorous intensity/moderate duration (P<.001). Weight loss was significant within all groups, but there
was no significant effect of either exercise duration or exercise intensity
on changes in body weight between groups. A similar pattern of change in BMI
was observed (Table 4).
Change in Cardiorespiratory Fitness
Compared with baseline, cardiorespiratory fitness significantly increased
following both 6 months and 12 months of treatment. All groups showed significant
within-group mean (SD) percentage increases in oxygen consumption following
12 months of treatment (vigorous intensity/high duration = 22.0% [19.9%];
moderate intensity/high duration = 14.9% [18.6%]; moderate intensity/moderate
duration = 13.5% [16.9%]; vigorous intensity/moderate duration = 18.9% [16.9%])
(P = .04). However, there were no significant effects
of either exercise intensity (P = .11) or exercise
duration (P = .35) on changes in cardiorespiratory
fitness between groups across 12 months of treatment (Table 4).
Exercise Dose-Response Results
In post hoc analysis, participants were grouped based on the amount
of physical activity that was classified as at least moderate intensity based
on the 7-day physical activity recall completed at both 6 and 12 months. Participants
were placed into the following groups: (1) averaging less than 150 min/wk
for both 6 and 12 months (n = 31); (2) averaging 150 min/wk or more at month
6 and less than 150 min/wk at month 12, or averaging less than 150 min/wk
at month 6 and 150 min/wk or more at month 12 (n = 81); (3) averaging 150
min/wk or more for both 6 and 12 months (n = 33); (4) averaging 200 min/wk
or more for both 6 and 12 months (n = 51). There was a significant difference
in minutes per week of at least moderate intensity exercise between groups
at month 6 and month 12 (P<.05).
Change in body weight and BMI are presented in Figure 3 and Table 5.
After Bonferroni adjustment for multiple comparisons, weight loss at 12 months
was significantly greater in the group with 200 min/wk or more of exercise
compared with both the group with less than 150 min/wk of exercise and the
other (inconsistent) exercise group. Weight loss in the group with 150 min/wk
or more of exercise did not differ from other groups.
Percentage change in cardiorespiratory fitness was significantly greater
at 12 months in the group with 200 min/wk or more of exercise compared with
the group with less than 150 min/wk of exercise (P =
.007) and the other group (P = .003). Percentage
change in fitness in the group with 150 min/wk or more of exercise was not
significantly different compared with the other groups (Table 5).
Analysis of energy intake showed no significant difference between groups.
When collapsed across all groups, mean (SD) baseline energy intake was 2118
(849) kcal/d and was reduced to 1480 (552) kcal/d at 6 months and 1456 (500)
kcal/d at 12 months.
While exercise is established as an important component of a behavioral
weight loss program, the optimal amount of exercise necessary to improve long-term
weight loss has yet to be determined. In this study examining the impact of
prescribing durations of exercise (moderate vs high) and 2 intensities of
exercise (moderate vs vigorous) on 12-month weight loss in previously sedentary
and overweight women, higher amounts of exercise resulted in a 10% weight
loss compared with an 8% weight loss for a lesser amount of exercise, but
this difference was not statistically significant.
Previous studies examining varying intensities of exercise on changes
in body weight and body composition typically did not exceed 6 months in duration,
and showed no effect for exercise intensity on body weight or body composition.7,12 Unlike these previous studies, the
current study included a strong dietary component in the intervention and
was significantly longer (12 months), yet higher intensity exercise did not
significantly increase weight loss. This finding may be a result of the difference
in exercise intensity not resulting in a difference in energy expenditure.
While exercise has been shown to be a significant predictor of long-term
weight loss, maintaining reductions in energy intake may be equally important.
The lack of a significant difference in 12-month weight loss between the 4
intervention groups may be a result of all groups maintaining reductions in
energy intake. Recently, Jakicic et al13 demonstrated
that both exercise and eating behavior significantly contribute to 18-month
weight loss. Moreover, McGuire et al14 reported
that reductions in energy expenditure and increases in intake of dietary fat
were associated with weight regain in participants in the National Weight
Control Registry. However, energy intake data should be interpreted with caution
because overweight adults underestimate their energy intake by approximately
300 to 500 kcal/d.15
There is limited evidence from long-term clinical trials to support
the recommendation of 30 min/d of moderate intensity physical activity4,16 or 60 min/d to enhance weight loss5 when incorporated into a standard behavioral weight
loss program that includes a dietary component. Our findings suggesting that
long-term weight loss is improved as exercise participation increases appear
to be consistent with the recommendation by the Institute of Medicine and
confirms previously published results.9,17
The results of this study also have important implications independent
of the effects of the exercise interventions on changes in body weight. Literature
suggests that exercise and improvements in cardiorespiratory fitness may enhance
health independent of body weight.18-21 The
current study showed that all levels of exercise that were prescribed resulted
in significant improvements in cardiorespiratory fitness.
This study also has several limitations. The lack of a diet-only comparison
group prevents this study from determining the effect of different durations
and intensities of exercise on body weight vs a nonexercise intervention.
This study also used an intensive behavioral intervention to maximize exercise
participation, and this approach may not be practical in most clinical settings.
Therefore, it may be important to examine the cost-effectiveness of these
intensive interventions in future weight loss studies. In addition, because
the majority of exercise performed in this study was brisk walking, the effect
of other forms of exercise (eg, resistance exercise) on long-term changes
in body weight could not be determined. Moreover, body composition data are
not available across this 12-month study, and therefore the effect of exercise
intensity and duration on these parameters cannot be examined.
The results of this study have implications for prescription of exercise
for sedentary, overweight adults engaging in weight loss efforts. Our results
suggest that moderate to high doses of exercise in combination with a decrease
in energy intake resulted in 8% to 10% reductions in body weight following
a 12-month intervention. Moreover, participants randomized to vigorous exercise
intensity did not have greater weight loss than those randomized to a similar
dose of exercise performed at a moderate intensity. However, when data were
analyzed based on the amount of exercise performed, greater levels of exercise
were associated with a greater magnitude of weight loss following 12 months
of treatment. Thus, interventions should initially target the adoption and
maintenance of at least 150 min/wk of moderate intensity exercise, and when
appropriate, eventually progress to exercise levels consistent with the Institute
of Medicine's recommendation of 60 min/d.
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