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Jakicic JM, Winters C, Lang W, Wing RR. Effects of Intermittent Exercise and Use of Home Exercise Equipment on Adherence, Weight Loss, and Fitness in Overweight Women: A Randomized Trial. JAMA. 1999;282(16):1554–1560. doi:10.1001/jama.282.16.1554
Context Enhancing participation in long-term exercise may translate into improved
long-term weight loss in overweight adults.
Objectives To compare the effects of intermittent with traditional continuous exercise
on weight loss, adherence, and fitness, and to examine the effect of combining
intermittent exercise with that using home exercise equipment.
Design Randomized trial from September 1996 through September 1998.
Setting and Participants A total of 148 sedentary, overweight (mean [SD] body mass index, 32.8
[4.0] kg/m2) women (mean [SD] age, 36.7 [5.6] years) in a university-based
weight control program.
Interventions Eighteen-month behavioral weight control program with 3 groups: long-bout
exercise (LB), multiple short-bout exercise (SB), or multiple short-bout exercise
with home exercise equipment (SBEQ) using a treadmill.
Main Outcome Measures Body weight, body composition, cardiorespiratory fitness, and exercise
Results Of 148 subjects, 115 (78%) completed the 18-month program. At 18 months,
mean (SD) weight loss was significantly greater in subjects in the SBEQ group
compared with subjects in the SB group (−7.4 [7.8] kg vs −3.7
[6.6] kg; P<.05). Mean (SD) weight loss for subjects
in the LB group (−5.8 [7.1] kg) was not significantly different than
for subjects in the SB or SBEQ groups. Subjects in the SBEQ group maintained
a higher level of exercise than subjects in both the SB and LB groups (P<.05) at 13 to 18 months of treatment. All groups showed
an increase in cardiorespiratory fitness from baseline to 18 months, with
no difference between groups. Mean (SD) weight loss at 18 months was significantly
greater in individuals exercising more than 200 min/wk throughout the intervention
(−13.1 [8.0] kg) compared with individuals exercising 150 to 200 min/wk
(−8.5 [5.8] kg) or less than 150 min/wk (−3.5 [6.5] kg) (P<.05).
Conclusions Compared with the LB group, subjects in the SB group did not experience
improved long-term weight loss, exercise participation, or cardiorespiratory
fitness. Access to home exercise equipment facilitated the maintenance of
SB, which may improve long-term weight loss. A dose-response relationship
exists between amount of exercise and long-term weight loss in overweight
A significant health risk accompanies a body mass index (BMI) in excess
of 25 kg/m2,1 and more than 50%
of adults in the United States are overweight by this criterion.2,3
Despite the short-term effectiveness of behavioral interventions for treating
obesity,1 many individuals regain significant
weight within a 1-year period.4,5
Exercise enhances short-term weight loss when combined with dietary modification
and is one of the best predictors of long-term maintenance of weight loss.6 However, exercise adherence in overweight adults is
less than desirable.7
Public health guidelines recommend the accumulation of physical activity,8 which may be easier to achieve, given the time constraints
of many sedentary individuals. Recent evidence suggests that exercise accumulation
combined with dietary modification may be effective at improving short-term
exercise adherence and weight loss in overweight adults.9
However, the long-term implications of multiple short bouts of exercise on
these parameters in overweight adults have not been examined. Cross-sectional
and laboratory-based studies have suggested that providing access to exercise
equipment may improve exercise participation10,11
by making exercise more convenient. However, we are unaware of any randomized
clinical trials that have examined the effectiveness of home exercise equipment
on exercise adherence rates.
This study was designed to examine whether exercise performed in multiple
short bouts compared with exercise performed in 1 long bout would improve
weight loss in overweight women after 18 months and to deter mine whether
overweight women using home exercise equipment during short bouts of exercise
would show improved weight loss after 18 months. Secondary outcomes included
exercise participation and cardiorespiratory fitness.
Adult women were recruited for this study through advertisements in
local newspapers. Subjects were 25 to 45 years old, had body weights 20% to
75% higher than ideal body weight,12 and were
sedentary (reported exercising <20 min/d on <3 d/wk for the previous
6 months). Women were excluded if they had medical conditions that would limit
their ability to participate in this study; were taking medication that would
affect body weight, other metabolic parameters, or both; had personal commitments
that would limit optimal participation; or were pregnant within the previous
3 months, currently pregnant, or planned on becoming pregnant in the following
18 months. Subjects provided written consent from their personal physicians
prior to participating in this study. Subjects' written informed consent was
obtained, and all procedures were approved by the institutional review board
at the University of Pittsburgh.
Subjects were randomly assigned to 1 of 3 groups. All subjects were
prescribed a similar volume of exercise. The 3 groups differed in the way
the exercise was prescribed (number of exercise sessions per week, duration
of exercise sessions, and the availability of home exercise equipment). The
exercise in all groups was home-based, and subjects were instructed to choose
a mode of exercise similar to brisk walking.
Forty-nine subjects were instructed to exercise 5 d/wk; duration progressed
from 20 min/d during weeks 1 through 4, to 30 min/d during weeks 5 through
8, to 40 min/d for the duration of this study. Participants performed the
exercise in 1 long bout.
Fifty-one subjects in this group were instructed to exercise 5 d/wk,
and duration of the exercise progressed from 20 min/d to 40 min/d by the ninth
week of the program. However, rather than exercising continuously for the
prescribed duration, subjects were instructed to divide the exercise into
multiple 10-minute bouts that were performed at convenient times throughout
the day. Therefore, subjects were instructed to progress from 2 to 4 exercise
bouts per day by week 9.
The exercise prescription was identical to the exercise prescribed for
the short-bout group in terms of days per week, duration per day, and number
of bouts of exercise. The 48 subjects in this group were also provided with
motorized home treadmills that were delivered to subjects' homes and maintained
by the investigators during the 18-month intervention.
All subjects participated in an 18-month behavioral weight-loss program
that had components common to all participants. Subjects attended weekly group
treatment meetings during months 1 through 6, biweekly meetings during months
7 through 12, and monthly meetings during months 13 through 18. These group
meetings focused on behavioral strategies for modifying eating and exercise
behaviors and were led by nutritionists, exercise physiologists, and behavioral
therapists. When a subject missed a group meeting, she was contacted in an
attempt to schedule a makeup session.
All groups were instructed to reduce both daily energy and fat intake.
Subjects weighing at least 90 kg at baseline were prescribed an intake of
6276 kJ/d, whereas subjects weighing less than 90 kg at baseline were prescribed
an intake of 5021 kJ/d. This prescribed energy intake would create a 2092-
to 4184-kJ deficit per day (0.45-0.9 kg weight loss per week)13
and does not go below the minimal recommended energy intake of 5021 kJ/d.13 Subjects were prescribed a fat intake goal of 20%
of total energy intake. Both the energy and fat intake prescribed have been
shown to promote significant weight loss in a previous study.9
Subjects were instructed to record their dietary intake in a daily food diary,
which were reviewed on a weekly basis by the interventionists, who provided
Weight was assessed at baseline and 6, 12, and 18 months to the nearest
0.11 kg using a calibrated balance-beam scale. Height was assessed using a
calibrated stadiometer on subjects standing upright and not wearing shoes.
Body composition was assessed at baseline, 6 months, and 18 months using
a dual-energy x-ray absorptiometer. A urine pregnancy test was performed immediately
prior to a total body scan. The mode of the baseline scan was made according
to the recommendations outlined in the operator's manual. Scans at 6 months
and 18 months were performed at the scanning mode that was used at baseline.
Girth measurements of the waist and hip14
were performed at baseline, 6 months, and 18 months and were assessed using
a tape measure. Two measurements were taken at each site. The average of these
2 measurements was used for data analysis.
Cardiorespiratory fitness was assessed at baseline, 6 months, and 18
months using a submaximal graded exercise test on a cycle ergometer.13 Initial work rate was 150 kg × min−1 and increased by the same at 3-minute intervals until the subject achieved
80% of age-predicted maximal heart rate.13
Heart rate was assessed using a 12-lead electrocardiogram,15
and oxygen consumption (O2) was also assessed. A linear relationship
exists between heart rate and O2 in overweight adults.16 Therefore, linear regression, incorporating the heart
rate and O2 collected at each minute of exercise and at the point
of termination, was used to assess the relationship between heart rate and
O2 for the prediction of peak O2 (predicted O2peak).
Dietary intake was assessed at baseline, 6 months, and 18 months using
the Block Food Frequency Questionnaire.17
Subjects recorded the exercise they performed in a log that was collected
by the investigators at each scheduled visit and used to compute the amount
of weekly exercise performed by each participant.
Triaxial accelerometers were used to verify the weekly exercise logs
during months 1 through 6. Subjects were assigned to wear the device for a
randomly selected 1-week period within the initial 6 months of treatment.
Minute-by-minute data were collected, and a computer program developed in
our laboratory was used to identify activity periods that were consistent
with the exercise prescription. These results were compared with the exercise
log completed during the same week that the device was worn.
Leisure-time physical activity (LTPA) was assessed at baseline, 6 months,
and 18 months using the Paffenbarger Questionnaire.18
Data were analyzed using SPSS version 8.0 software (SPSS Inc, Chicago,
Ill). Based on descriptive data, skewed data were log transformed prior to
analysis. Comparison of baseline data was performed using a 1-way analysis
of variance (ANOVA). The a priori hypotheses were examined using a 2-factor
(group × time) repeated measures ANOVA, and additional analyses were
performed using 1-way ANOVA and Duncan post hoc analysis. A χ2test
was used to assess distribution patterns for subjects who dropped out and
attainment of intervention goals,19 and these
results were confirmed using Fisher exact tests.19
Statistical significance was defined as P≤.05.
All data were analyzed using an intent-to-treat analysis unless otherwise
specified. For missing data, we assumed that there was a return to baseline
values for weight, body composition, fitness, dietary intake, and LTPA or
that there was no exercise performed (exercise logs).
A power analysis based on weight loss at 18 months (the primary hypothesis)
was conducted prior to recruitment. This analysis indicated that 50 subjects
per group would provide statistical power of 70% to detect an effect size
of 0.63 for differences in weight loss at 18 months between groups.
At baseline, there were no significant differences between groups (Table 1). Overall, 115 subjects (78% of
148 subjects randomized) completed 18 months of treatment, with no significant
difference in attrition rates between the groups (P
= .12). Reasons for not completing the study are shown in Figure 1. There was no significant difference in attendance at the
behavioral group sessions among the intervention groups across the 18 months
of treatment. The mean (SD) percentage of sessions attended was 67.1% (23.3%)
for the LB group, 70.9% (24.1%) for the SB group, and 71.7% (21.9%) for the
When the 3 treatment groups were included in the model, there was a
significant group × time interaction for change in body weight (P<.01) (Figure 2).
There was no significant difference between the LB and SB groups for mean
(SD) weight loss at either 6 months (LB, −8.2 [5.5] kg; SB, −7.5
[5.4] kg) or 18 months (LB, −5.8 [7.1] kg; SB, −3.7 [6.6] kg).
Weight loss at 6 months was not significantly different between the SBEQ (−9.3
[5.6] kg) and SB (−7.5 [5.4] kg) groups (P
= .11). However, weight loss at 18 months was significantly greater in the
SBEQ group (−7.4 [7.8] kg) compared with the SB group (−3.7 [6.6]
kg) (P<.05). Post hoc analysis showed no significant
difference in weight loss at 6 or 18 months between the LB and SBEQ groups.
In analyses using only the 115 subjects who completed 18 months of treatment,
there were no significant difference in weight loss at 6 months among the
groups (LB, −10.2 [4.2] kg; SB, −9.3 [4.5] kg; SBEQ, −10.2
[5.2] kg; P = .63). Weight regained during months
6 to 18 did not differ between the LB (2.6 [5.5] kg) and SB (4.1 [5.6] kg)
groups. However, there was significantly less weight regain in the SBEQ group
(1.8 [4.7] kg) compared with the SB group (P = .05)
but no significant difference between the SBEQ and LB groups.
There were significant changes in percentage of body fat, fat mass,
and lean body mass over time (P<.001), but no
change in bone mineral content (Table 2). In addition, there was a significant group × time interaction
when all groups were included in the analysis. When the a priori hypothesis
comparing the LB and SB groups was examined, there was no significant difference
for measures of body composition. However, changes in percentage of body fat
and fat mass were greater in the SBEQ group compared with the SB group, and
no difference for lean body mass or bone mineral content. Comparison of the
LB and SBEQ groups revealed no differences. Despite changes over time for
waist girth and waist-to-hip ratio (P<.001), there
were no differences in the pattern of change (Table 2).
The duration of exercise for weeks 1 through 4 was significantly greater
in the SB compared with both LB and SBEQ groups (P<.05)
(Figure 3). There were no significant
differences among groups for weeks 5 through 8, weeks 9 through 24, or months
7 through 12. However, exercise duration was greater in SBEQ compared with
both LB and SB groups for months 13 through 18 (P<.05).
After duration (mean [SD]) peaked during weeks 9 through 24, all groups showed
a decrease during months 7 through 12 (LB, −41.7 [72.5] min/wk; SB, −31.2
[104.0] min/wk; SBEQ, −45.8 [74.0] min/wk) with no significant differences
among groups. However, the decrease in duration of exercise during months
13 through 18 was significantly greater in the SB group (−68.7 [95.1]
min/wk) compared with the SBEQ group (−31.6 [58.7] min/wk) (P<.05); the LB group (−42.2 [73.7] min/wk) did not differ
significantly from either the SB or SBEQ groups (P>.09).
A similar percentage of subjects in each group (LB, 73.5%; SB, 78.4%;
SBEQ, 75.0%) achieved a level of exercise of at least 150 min/wk8
during weeks 5 through 24; 47.2%, 62.5%, and 72.2% maintained this level during
months 7 through 12 in the LB, SB, and SBEQ groups, respectively (P = .09). Of those subjects achieving at least 150 min/wk of exercise
during both weeks 5 through 24 and months 7 through 12, 70.6%, 64.0%, and
73.1% maintained this level during months 13 through 18 in the LB, SB, and
SBEQ groups, respectively (not significant; P = .77).
There was also no difference between groups (LB, 24.5%; SB, 31.4%; SBEQ, 39.6%)
for the number of subjects achieving at least 150 min/wk of exercise at all
3 time intervals (weeks 5-24, months 7-12, months 13-18).
Among the 115 subjects who completed 18 months of treatment, both the
SB and SBEQ groups exercised for a longer duration per session than prescribed,
whereas the LB group exercised for a longer duration (minutes/session) than
both the SB and SBEQ groups (Table 3).
Both the SB and SBEQ groups exercised for more sessions per week than the
Across the entire 18 months of treatment, there was no significant difference
between the LB (74.3% [28.1%]) and SB (75.9% [26.4%]) groups for the percentage
(mean [SD]) of exercise sessions in which walking was the selected activity.
However, the SBEQ group reported selecting walking for exercise more often
(93.7% [10.8%]) than the LB group (P<.05), but
there was no difference between the SB and SBEQ groups across the 18-month
period. As expected, the SBEQ group reported using a treadmill for exercise
(41.6% [31.7%]) more than both the LB (8.1% [20.5%]) and SB (10.7% [19.5%])
groups during the 18-month period (P<.05).
The triaxial accelerometer was worn by 111 of the 115 individuals who
completed the intervention; 3 individuals in the LB group and 1 individual
in the SB group did not wear the device properly, refused to wear it, or both.
There was no difference between the accelerometer data and self-reported data,
respectively, for the total amount of exercise completed per week (mean [SD])
by the LB (130.0 [66.7] vs 154.5 [69.4] min/wk), SB (189.9 [94.5] vs 185.5
[141.9] min/wk), and SBEQ (198.5 [131.7] vs 181.7 [96.6] min/wk) groups. In
addition, wearing the accelerometer did not increase exercise participation
compared with the other weeks when the exercise prescription was identical
(174.5 [106.4] min/wk vs 197.8 [86.9] min/wk, respectively) (P<.01). This pattern was similar between treatment groups.
Analysis of LTPA revealed no significant group or group × time
interaction. However, there was a significant time effect (P<.001) for LTPA that increased significantly from 0 to 18 months
in the LB (2251.0 [2108.7] to 6378.1 [5816.2] kJ/wk), SB (2680.7 [2262.7]
to 5777.3 [4916.2] kJ/wk), and SBEQ (2723.8 [3333.0] to 6199.9 [5432.9] kJ/wk)
All groups significantly decreased total energy intake and the percentage
of energy consumed as fat (P<.001). However, the
nonsignificant group × time interaction indicates that the change in
energy intake measured at 0, 6, and 18 months was similar among the LB (7308.6
[3197.4] to 5446.3 [2572.3] to 5874.8 [2946.4] kJ/d), SB (8169.7 [4719.6]
to 5714.5 [2249.3] to 6716.6 [4491.1] kJ/d), and SBEQ (8003.6 [4960.1] to
6144.2 [4777.3] to 6178.5 [4448.4] kJ/d) groups. Similar results were shown
for percentage of energy consumed as fat for the LB (37.9% [6.7%] to 31.7%
[8.9%] to 33.6% [8.8%]), SB (35.3% [7.1%] to 28.8% [8.5%] to 32.3% [8.2%]),
and SBEQ (35.1% [6.7%] to 30.9% [8.6%] to 32.9% [7.4%]) groups.
Increases in predicted O2peak (mL ×kg−1 × min−1) from 0 to 6 months were 18.9% (22.3%)
in the LB group, 9.5% (15.7%) in the SB group, and 16.0% (14.4%) in the SBEQ
group. All groups significantly increased cardiorespiratory fitness compared
with baseline within the initial 6 months of treatment (P<.05). The magnitude of this increase was significantly different
between the LB and SB groups (P<.05). Predicted
O2peak remained significantly (P<.05)
increased at 18 months compared with 0 months (LB, 9.9% [22.7%]; SB, 6.3%
[13.1%]; SBEQ, 11.5% [17.1%]; P≤.007), with no
difference between groups.
Based on self-reported exercise at each of the 6-month intervals (weeks
5-24, months 7-12, months 13-18), subjects were divided into 1 of the following
groups: (1) averaging less than 150 minutes of exercise per week at all of
the 6-month intervals (EX<150), (2) averaging at least 150 minutes of exercise
per week at all of the 6-month intervals but not more than 200 minutes per
week of exercise at all of the 6-month intervals (EX≥150), or (3) averaging
at least 200 minutes per week at all of the 6-month intervals (EX≥200).
There was a significant group × time interaction (P<.001) for self-reported exercise and a significant (P<.001) decrease in both the EX<150 (0-6 months, 182.7 [81.2];
7-12 months, 129.5 [75.5]; and 13-18 months, 52.3 [62.3] min/wk) and EX≥150
(0-6 months, 233.3 [62.2]; 7-12 months, 209.3 [39.0]; and 13-18 months, 188.0
[35.6] min/wk) groups. Compared with both the EX<150 and EX≥150 groups,
exercise in the EX≥200 group was significantly greater (P<.05) and remained unchanged across time (0-6 months, 291.4 [69.3];
7-12 months, 282.6 [65.9]; and 13-18 months, 281.0 [70.8] min/wk). Following
18 months, there was no significant difference in estimated energy used (kJ/wk)
during LPTA between the EX≥150 (9025  kJ/wk) and EX≥200 (11,004
 kJ/wk) groups, and both groups used significantly more energy than
the EX<150 group (5515  kJ/wk) (P<.05).
There was a significant group × time interaction (P<.001) for weight loss, suggesting that the pattern of weight loss
across the groups was significantly different (Figure 4). Weight loss at 18 months was significantly greater in
the EX≥200 group (−13.1 [8.0] kg) compared with both the EX<150
(−3.5 [6.5] kg) and EX≥150 (−8.5 [5.8] kg) groups (P<.05). There was no effect of randomized group assignment (LB,
SB, SBEQ) on these results.
It has been suggested that a minimum of 150 minutes of moderate-intensity
physical activity accumulated throughout the week can improve health.8 We have previously shown that prescribing exercise
in multiple short bouts per day increases exercise participation in overweight
women during a 20-week period.9 Despite other
studies that show the efficacy of short bouts of exercise,20,21
to our knowledge, no other studies have examined whether this strategy increases
long-term exercise participation or weight loss. As has been done in recent
physical activity intervention studies,22 we
used a home-based activity program with a strong behavioral component to compare
continuous (LB) and intermittent (SB) exercise. Initial results showed statistically
significant higher levels of exercise in the SB compared with the LB group.
However, compared with the LB group, the SB group did not statistically increase
the minutes of exercise per week after the first 4 weeks, nor did it increase
the number of individuals averaging a minimum of 150 min/wk of exercise throughout
the entire 18-month intervention. Therefore, the use of short bouts of exercise
performed multiple times throughout the day may not increase long-term exercise
adherence beyond what can be achieved with traditional long bouts of exercise
coupled with a strong behavioral program. Moreover, there was no significant
difference in weight loss following 18 months of treatment when the SB group
was compared with the LB group.
Our study also showed that multiple short-bout exercise with home exercise
equipment improves long-term weight loss and fat loss compared with short
bouts. This may be a result of the SBEQ group showing less decline in exercise
participation during the final 6 months of treatment (months 13-18) compared
with the SB group. Therefore, the incorporation of short bouts of exercise
may be most effective when participants have access to home exercise equipment.
Having access to exercise equipment may make exercise more convenient,10,11 which may facilitate the adoption
of multiple short bouts of exercise. However, because long-bout exercise was
not combined with exercise equipment, the effectiveness of this exercise intervention
in overweight women remains unclear.
Despite differences in exercise participation between the groups, additional
factors such as dietary intake and attendance at group meetings also could
have contributed to differences in weight loss. While recognizing the difficulty
of assessing dietary intake in a free-living environment using questionnaires,23 we observed no difference in dietary intake between
the intervention groups at any time point. In addition, we observed no difference
between groups for the number of behavioral sessions that were attended.
Although short-bout exercise was not significantly better than long-bout
exercise with regard to weight loss, exercise participation, or fitness, this
study suggests that long-term results obtained with short bouts were as beneficial
as those obtained with long bouts in overweight women. Therefore, short bouts
can be used as an option for incorporating exercise into one's lifestyle.
Dunn et al22 have shown that lifestyle physical
activity is as effective as structured exercise for improving fitness in adults.
These nontraditional methods of prescribing exercise should be considered
when traditional methods of exercise prove to be ineffective at increasing
Our study also demonstrated that achieving a minimum of 150 min/wk of
exercise throughout the 18-month program enhanced weight loss compared with
not maintaining this minimal level of exercise. However, achieving higher
levels of exercise resulted in even greater weight loss at 18 months. These
results indicate that overweight individuals can achieve relatively high levels
of exercise per week. Moreover, the amount of exercise necessary for enhancing
long-term weight loss may be greater than the minimum cited in public health
recommendations,8 which supports the findings
of Klem et al24 and Schoeller et al.25
In summary, this study showed that dietary modification combined with
exercise performed in short bouts does not improve long-term weight loss compared
with exercise performed in longer bouts. However, the addition of a home treadmill
to the multiple short-bout exercise intervention (SBEQ) minimized reductions
in long-term exercise participation and improved long-term weight loss. This
study has also demonstrated that either continuous (LB) or intermittent exercise
(SB, SBEQ) can significantly improve cardiorespiratory fitness, which is consistent
with previous findings.9,20 These
results indicate that there are a number of options for effectively incorporating
exercise into a behavioral weight loss program, and these should be considered
when developing behavioral intervention strategies for increasing long-term
weight loss and exercise participation in overweight adult women.
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