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Nonexercise Energy Expenditure and Physical Activity in the Midwest Exercise Trial 2

WILLIS, ERIK A.1; HERRMANN, STEPHEN D.2; HONAS, JEFFERY J.1; LEE, JAEHOON3; DONNELLY, JOSEPH E.1; WASHBURN, RICHARD A.1

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Medicine & Science in Sports & Exercise: December 2014 - Volume 46 - Issue 12 - p 2286-2294
doi: 10.1249/MSS.0000000000000354
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Abstract

Exercise is recommended for weight management by several governmental agencies and professional organizations (1,6). Compared with weight loss induced by energy restriction, weight loss achieved by exercise is composed predominantly of fat mass, whereas fat-free mass is preserved (7) and resting metabolic rate (RMR) is generally unchanged (30) or slightly increased (27). These factors may be associated with improved long-term weight loss maintenance. However, several reports have demonstrated that the accumulated negative energy balance induced by an exercise intervention alone is less than that theoretically predicted for the imposed level of exercise-induced energy expenditure (3,18) most likely because of compensatory changes in energy intake, nonexercise energy expenditure (NEEx), or both. These compensatory changes could reduce the magnitude of exercise-induced weight loss. Compensatory changes in energy intake and/or NEEx are also suggested by studies reporting no additional weight loss with increased exercise dose (3,8,29).

As early as 1980, Epstein and Wing (11) suggested that a reduction on NEEx might compensate for prescribed exercise training, thus resulting in little to no change in total daily energy expenditure (TDEE) and no, or minimal, exercise-induced weight loss. Several short-term (2–14 d) (2,19–21,31,32,36,40), nonrandomized (4,5,13,17,22–24,26), and randomized trials (3,12,16,28,29,35) have evaluated the effect of exercise training on NEEx or nonexercise physical activity (NEPA) with mixed results. Irrespective of study design (i.e., short-term crossover, nonrandomized, and randomized trials), the majority of studies do not observe reductions in reported NEPA (3,19,20,29,36) or NEEx (5,12,16,17,21,24,28,31,32,35,40) in response to prescribed aerobic exercise. Studies that reported decreased NEEx (4,13,26) or NEPA (22,23) in response to prescribed exercise used nonrandomized designs and were generally conducted in small samples (≤15 per group) of overweight or obese older adults (i.e., >55 yr). Assessments of change in NEEx rather than those in NEPA in response to prescribed aerobic exercise are particularly relevant in the context of weight management. However, no trials have assessed NEEx using state-of-the-art measures of TDEE (doubly labeled water (DLW)), RMR (indirect calorimetry), and exercise energy expenditure (EEEx) (indirect calorimetry) (37). Data from the Midwest Exercise Trial-2 (MET-2) afforded an opportunity to examine the effect of prescribed aerobic exercise on both NEEx (DLW with both RMR and EEEx assessed by indirect calorimetry) and NEPA (accelerometer) in a sample of previously sedentary, overweight/obese young adult men and women. Briefly, MET-2 randomized overweight or obese individuals (body mass index (BMI), 25–40 kg·m−2) age 18–30 yr to 10 months, 5 d·wk−1 of supervised exercise intervention at two levels of EEEx (400 or 600 kcal per session) or nonexercise control. The primary aim of MET-2 was to evaluate the role of aerobic exercise without energy restriction on weight and body composition; however, several secondary outcomes, including changes in RMR, NEPA and NEEx, and energy intake, were included a priori in the original study design. MET-2 was powered to detect between-group differences in weight change over time and to determine whether weight change was equivalent in men and women. NEPA and NEEx were unpowered secondary outcomes. A detailed description of the design and methods for MET-2 (9) and the results for the primary aims (8) have been published previously. Data regarding changes in energy and macronutrient intake and the effect of changes in NEPA and NEEx on weight change will be reported separately.

METHODS

Participants

Participants were men and women (age, 18–39 yr; BMI, 25–40 kg·m−2) who were able to exercise and willing to be randomized into one of the three study groups. Potential participants were excluded for the following reasons: a history of chronic disease (i.e., diabetes, heart disease, etc.), elevated blood pressure (>140/90), lipids (cholesterol, >6.72 mM; triglycerides, >5.65 mM), or fasting glucose (>7.8 mM), use of tobacco products, taking medications that would affect physical performance (i.e., beta blockers, metabolism, thyroid, or steroids), inability to perform laboratory tests or participate in moderate- to vigorous-intensity exercise, and planned physical activity greater than 500 kcal·wk−1 as assessed by recall (33). Participants provided written informed consent before engaging in any aspect of the trial and were compensated for participation. The approval for this study was obtained from the human subjects committee of the University of Kansas—Lawrence.

Randomization and Blinding

Participants were stratified by sex and randomized by the study statistician (approximately 80% exercise; approximately 20% control). All participants were instructed to continue their typical patterns of dietary intake over the duration of the 10-month intervention. The blinding of participants to group assignment was not possible because of the nature of the intervention. However, both investigators and research staff were blinded at the level of outcome assessments, data entry, and data analysis.

Exercise Training

Participants completed 5 d·wk−1 of supervised exercise consisting primarily of walking and jogging. Alternate activities (e.g., elliptical, bicycle) were allowed for 20% of the exercise sessions. Exercise intensity was initially set at 70% HRmax and slowly progressed to 80% HRmax by month 5. Exercise progressed from 150 kcal per session at the intervention onset to the target EEEx (400 or 600 kcal per session) at the end of month 4 and remained at target for the final 6 months of the study. Exercise was supervised by trained research staff, and the duration and intensity of all exercise sessions were verified by an HR monitor (RS 400; Polar Electro Inc., Woodbury, NY). A valid exercise session was defined as ±4 beats per minute of target HR for a duration sufficient to achieve the target EEEx (400 or 600 kcal per session). The average duration of an exercise session after reaching the target EEEx was 39 ± 10 min in the 400-kcal-per-session group and 55 ± 12 min in the 600-kcal-per-session group. Because of the efficacy design, completion of ≥90% of exercise sessions was an a priori definition of per protocol; thus, our analysis included only participants meeting this criterion.

The duration of exercise required to elicit the targeted EEEx (either 400 or 600 kcal per session) was determined individually for each participant. At the baseline assessment, treadmill speed was set at 3 mph with 0% grade and was adjusted by increments of 0.5 mph and 1% grade until the participant reached 70% HRmax. HRmax was the highest HR rate achieved during the assessment of maximal aerobic capacity (9). EEEx was then assessed over a 15-min interval (1-min epochs) using a ParvoMedics TrueOne2400 indirect calorimetry system (ParvoMedics Inc., Sandy, UT). The average EEEx (kcal·min−1) over the 15-min interval was calculated from measured oxygen consumption and carbon dioxide production using the Weir equation (38). This value was used to provide the goal for the duration of exercise sessions for the first month of the intervention. For example, the prescribed EEEx during month 1 = 150 kcal per session, EEEx = 9.2 kcal·min−1, exercise duration = 150 kcal per session, divided by 9.2 kcal·min−1 = 16 min per session. Similar procedures to determine exercise duration, at either 70% or 80% HRmax, were conducted at the end of each month over the course of the 10-month intervention to adjust for potential effects of changes in both body weight and cardiovascular fitness on EEEx. All exercise sessions and assessments of EEEx were preceded by a brief warm-up on the treadmill (approximately 2 min, 3–4 mph, 0% grade). Treadmill speed and grade were subsequently increased to achieve the prescribed target HR.

Control group

Participants assigned to the nonexercise control group were instructed to continue their typical patterns for physical activity and dietary intake over the duration of the 10-month study. With the exception of assessment of EEEx, the same outcome assessments were completed in both the exercise and control groups.

Outcomes

All assessments were completed by trained research assistants.

RMR

RMR was assessed at baseline and 10 months by open-circuit indirect calorimetry. Participants reported to our laboratory between 6:00 and 10:00 a.m. after a 12-h fast and 48-h abstention from aerobic exercise (14) and rested quietly for 15 min in a temperature-controlled (21°C–24°C) isolated room. Subsequently, participants were placed in a ventilated hood for assessment of V˙O2 and V˙CO2 for a minimum of 35 min using a ParvoMedics TrueOne 2400 indirect calorimetry system (ParvoMedics Inc., Sandy, UT). The criterion for a valid RMR was a minimum of 30 min of measure values with <10% average SD across the last 30 min of the minimum 35-min assessment. RMR (kcal·d−1) was calculated using the Weir equation (38).

TDEE/NEEx

TDEE was assessed by DLW over a 14-d period at baseline and 10 months. The end study assessment (10 months) was obtained during the final 2 wk of the exercise training protocol. Participants reported to our laboratory between 8:00 and 9:00 a.m. after an overnight fast. Baseline urine specimens were collected from each participant before oral dosing with a mixed solution of 2H218O. The isotope was given to each participant on the basis of body weight (0.10 g·kg−1 of 2H2O and 0.15 g·kg−1 H218O) and was followed with a rinse solution of 100 mL of tap water. A weighed 1:400 dilution of each participant’s dose was prepared, and a sample of the tap water was stored at −70°C for later analysis. Additional urine samples were collected on days 1 and 14. On these days, two urine samples were collected at least 3 h apart. All urine samples were stored in sealed containers at −70°C before analysis. Samples were analyzed in duplicate for 2H2O and H218O by isotope ratio mass spectrometry, as previously described by Herd et al. (15). TDEE was estimated using the equation of Elia (10), as follows: total EE (MJ·d−1) = (15.48/RQ + 5.55) × rCO2 (L·d−1). NEEx, i.e., energy expenditure not associated with exercise training, was calculated as follows: [(TDEE × 0.9) − RMR] − net EEEx (EEEx − RMR). This approach assumes that the thermic effect of food represents 10% of TDEE (39). EEEx for exercise sessions during the DLW assessment period was assessed by indirect calorimetry, as described previously. The duration of exercise periods was obtained from exercise logs maintained by research staff and verified by an HR monitor. Note that net EEEx at baseline equals zero.

NEPA/sedentary time

NEPA was assessed by a portable accelerometer (ActiGraph GT1M; ActiGraph LLC, Pensacola, FL). The GT1M is a small, lightweight (3.8 × 3.7 × 1.8 cm, 27 g), uniaxial piezoelectric accelerometer, which measures and records vertical accelerations from approximately 0.05g to 2.0g with a frequency response ranging from 0.25 to 2.50 Hz reflected as activity counts per minute (cpm). Accelerometers were worn on an elastic belt over the nondominant hip for seven consecutive days at baseline, 3.5, 7, and 10 months. The data collection interval was set at 1 min, with a minimum of 10 h constituting a valid monitored day. Three valid days were required to be included in the accelerometer analysis. Nonwear time was identified as ≥60 consecutive minutes with 0 cpm, with allowance for 1–2 min of accelerometer counts between 0 and 100 (34). Data were downloaded using ActiGraph software and processed using a custom SAS program developed by our group. The NEPA data were obtained by removing accelerometer data over the duration of exercise sessions, which were identified via exercise logs maintained by research staff and verified by an HR monitor from the daily accelerometer data. The NEPA measures were then created as the time spent in different levels of physical activity not including time spent in exercise prescribed by the intervention. We assessed both average counts per minute (raw and percent) and nonexercise time spent sedentary (<100 cpm) and in light (100–2019 cpm), moderate (>3 METs, 2020–5999 cpm), and vigorous PA (>6 METs, >5999 cpm) (34). A mean of approximately 6 valid days of accelerometer data was available. The number of valid days did not differ by intervention group over the four assessment time points. There were no significant differences in wear time between groups or over time.

Statistical Analysis

ANOVA and t-tests were conducted to compare NEEx, TDEE, and RMR between and within groups. Then, general linear modeling was used to assess the effects of age, sex, group, and changes in weight and aerobic capacity on changes in NEEx and TDEE. General linear mixed modeling was used to examine differences between groups (group effect), changes over time (time effect), and group–time interaction for NEPA measures including average counts per minute (raw and percent) and time spent in sedentary, light, moderate, and vigorous PA. The raw or model-based group means were compared pairwise using a Bonferroni correction for inflation in Type I error. Statistical significance was determined at 0.05 alpha level, and all analyses were performed using SAS software, version 9.3 (SAS Institute Inc., Cary, NC).

RESULTS

One hundred and forty-one individuals were randomized to one of the three study groups. Ninety-two individuals (65.2%) complied with the study protocol and completed all assessments for the primary outcomes (i.e., weight, body composition). The baseline characteristics of the 92 who completed all assessments are presented in Table 1. There were no significant difference in baseline descriptive characteristics (age, body weight, BMI, body composition, aerobic capacity) between the three study groups or between those individuals who completed the study and those who did not (9). Because of technical problems or failure to comply with the assessment protocols, this report includes DLW data from 83 participants at baseline (400 kcal per session, n = 34; 600 kcal per session, n = 34; control, n = 15) and 79 participants at 10 months (400 kcal per session, n = 30; 600 kcal per session, n = 32; control, n = 17) as well as accelerometer data from 92 participants at baseline (400 kcal per session, n = 37; 600 kcal per session, n = 37; control, n = 18) and 86 participants at 10 months (400 kcal per session, n = 34; 600 kcal per session, n = 37; control, n = 15). There were no differences in baseline characteristics or weight loss between those that completed all tests and those with missing data.

TABLE 1
TABLE 1:
Baseline sample characteristics.

Energy Expenditure

A summary of the ANOVA and paired-samples t-test results for NEEx, TDEE, and RMR is presented by group and sex in Table 2 and Figure 1.

TABLE 2
TABLE 2:
Change in TDEE, RMR, and NEEx over 10 months by intervention group and sex.
FIGURE 1
FIGURE 1:
Change in energy expenditure (NEEx, RMR, and TDEE) from month 0 to 10 by group and sex.Error bars represent SE.

NEEx

There were no significant between- or within-group differences for change in NEEx in the total sample or in men and women. In the total sample, NEEx increased in the 400-kcal-per-session group (+16 ± 511 kcal·d−1), decreased in the 600-kcal-per-session group (−37 ± 479 kcal·d−1), and decreased in controls (−107 ± 667 kcal·d−1). The patterns of change in NEEx differed by sex. In men, NEEx decreased in both the 400- (−66 ± 578 kcal·d−1) and 600-kcal-per-session groups (−66 ± 533 kcal·d−1) and was essentially unchanged in controls (+11 ± 758 kcal·d−1). In women, NEEx increased in the 400-kcal-per-session group (+92 ± 445 kcal·d−1), was essentially unchanged in the 600-kcal-per-session group (−6 ± 432 kcal·d−1), and decreased in controls (−263 ± 549 kcal·d−1). Approximately 50.0% of the participants in the 400-kcal group, 38% in the 600-kcal group, and 44% in the control group increased NEEx over the 10-month intervention.

RMR

There were no significant between- or within-group differences for change in RMR in the total sample or in men or women. RMR decreased in both the 400- and 600-kcal-per-session groups, reflecting exercise-induced weight loss (approximately 5%) (8) and was essentially unchanged in controls, reflecting minimal weight gain in the control group (8).

TDEE

Results for change in TDEE varied by group and sex. In the total sample, TDEE increased significantly from baseline to 10 months in the 600-kcal-per-session group (+289 ± 434 kcal·d−1). The increase in TDEE in the 400-kcal-per-session group (+191 ± 614 kcal·d−1) and the decrease in TDEE in controls (−111 ± 588 kcal·d−1) were both nonsignificant. In men, there were no significant increases in TDEE in the 400-kcal-per-session (+62 ± 634 kcal·d−1), 600-kcal-per-session (+215 ± 510 kcal·d−1), and control groups (+18 ± 748 kcal·d−1), with no significant group differences for change in TDEE. In women, TDEE increased significantly in the 600-kcal-per-session group (+368 ± 336 kcal·d−1) and decreased significantly in controls (−283 ± 232 kcal·d−1). The increase in TDEE in the 400-kcal-per-session group (+312 ± 590 kcal·d−1) in women, although not statistically significant (P = 0.059), is of potential clinical relevance.

General Linear Modeling

General linear models including age, sex, group, change in weight, and change in aerobic capacity were examined to investigate the factors associated with changes in NEEx and TDEE. Decreased weight from baseline to 10 months was significantly associated with increased NEEx (P = 0.014). The participants’ age was significantly positively associated with change in TDEE (P = 0.025) (e.g., greater increases in older participants), whereas change in weight (P = 0.097), aerobic capacity (P = 0.084), and group (P = 0.090) were not.

General Linear Mixed Modeling

NEPA and sedentary time

As shown in Figure 2, NEPA (average cpm) decreased in controls and was essentially unchanged or slightly increased in the exercise intervention groups. There was a significant group–time interaction (P = 0.009), with significantly higher NEPA in the 600-kcal-per-session group compared with that in controls at 7 months (P < 0.001) and significantly higher NEPA in both the 400- (P = 0.043) and 600-kcal-per-session (P < 0.001) groups compared with that in controls at 10 months. Results in men were similar to those in the total sample. In men, there was a significant group–time interaction (P = 0.008), with significantly higher NEPA in the 600-kcal-per-session group versus controls at 10 months (P = 0.014). In women, there were no significant effects of group, time, and group–time interaction. Nevertheless, NEPA was significantly higher in the 600-kcal-per-session group versus controls at 3.5 (P = 0.013), 7 (P < 0.001), and 10 (P = 0.007) months.

FIGURE 2
FIGURE 2:
Mean accelerometer activity counts per minute at months 0, 3.5, 7, and 10 by group and sex.Error bars represent SE.

Figure 3 presents the duration (min) of NEPA spent in sedentary and light-, moderate-, and vigorous-intensity PA assessed by an accelerometer. This analysis was also performed using the percentage of time in these activity categories after removing the time spent in exercise training. The results for these two approaches were the same; thus, we have presented NEPA results as minutes per day because they are more easily interpreted. There were no significant effects for group, time, and group–time interaction for any intensity of PA. Nevertheless, sedentary time was significantly higher in the controls (model-based mean, 609 min·d−1) compared with that in the 600-kcal-per-session group (576 min·d−1) at 7 months (P = 0.033). Time spent in moderate NEPA in the 600-kcal-per-session group (37 min·d−1) was significantly greater than that in controls (29 min·d−1) at 10 months (P = 0.048). Approximately 79% of participants in the 400-kcal group, 54% in the 600-kcal group, and 47% of controls decreased time spent in sedentary activity over the 10-month intervention. Approximately 47% of participants in the 400-kcal group, 57% in the 600-kcal group, and 40% of controls increased the time spent in NEPA (light + moderate + vigorous).

FIGURE 3
FIGURE 3:
Time spent sedentary and in light, moderate, and vigorous activity at months 0, 3.5, 7, and 10 by group and sex.Error bars represent SE.

DISCUSSION

NEEx

We found no significant change in NEEx in a sample of initially sedentary, overweight, and obese young adults in response to 5 d·wk−1 of an aerobic exercise intervention (400 or 600 kcal per session) over 10 months. Results from the limited number of studies where NEEx was assessed by DLW have reported increased (24), decreased (4,13), and no change (40) in NEEx in response to aerobic exercise training. For example, Meijer et al. (24) reported a significant increase in NEEx in a small sample of adult men and women (n = 8) who completed a 5-month training program in preparation for running a half-marathon. Using a crossover design, Whybrow et al. (40) found no significant change in NEEx in a small sample (n = 12) of normal/overweight adults who completed a 14-d exercise intervention at two levels of EEEx. In a nonrandomized trial, Colley et al. (4) reported a significant decrease in NEEx in response to a 4-wk supervised moderate-intensity walking program (target EEEx, 1500 kcal·wk−1) in a small sample (n = 7) of overweight/obese women (mean age, 41.1 yr). Goran and Poehlman (13) also observed a significant reduction in NEEx in response to 3 d·wk−1 of a cycle ergometer exercise program (300 kcal per session) in a small sample (n = 5 women, n = 6 men) of older adults (approximately 65 yr).

The majority of studies where NEEx has been estimated using other less precise techniques, including accelerometry (16), a combination of accelerometry and HR monitoring (35), HR monitoring with individual HR energy expenditure calibration (17,21,31), or SenseWear Pro armband (5), have shown no change in NEEx in response to aerobic exercise training. However, Morio et al. (26) reported decreased NEEx assessed by a 7-d activity diary in response to moderate-intensity cycle ergometer training (3 d·wk−1, 14 wk) in a small sample of older (approximately 63 yr) men and women (n = 8 women, n = 5 men). Thus, the results of the current study, which suggest no significant change in NEEx in response to aerobic exercise training, are in agreement with the preponderance of the literature.

Our results, and those of others, should be interpreted with caution. The four other studies that have reported on the change in NEEx assessed by DLW in response to aerobic exercise training were generally conducted using nonrandomized designs in small samples (range, 7–12 participants per study) of normal-weight individuals (13,24,40). With the exception of the 5-month trial by Meijer et al. (24), these studies used relatively short exercise interventions (range, 14 d (40) to 8 wk (13)) and did not include assessments of EEEx by indirect calorimetry, which are necessary for accurate estimates of NEEx.

NEPA

In agreement with our results for change in NEEx, we found no change in NEPA or duration (min) of NEPA spent in sedentary, light, moderate, or vigorous activities, assessed by an accelerometer, resulting from participation in aerobic exercise training. NEPA tended to decrease in controls and remain relatively stable over the 10-month intervention in both exercise groups. Interestingly, we found no evidence that participating in an aerobic exercise intervention results in increased time spent sedentary as measured by accelerometry. In fact, sedentary time tended to increase in controls and decrease in the exercise groups, resulting in between-group differences at 7 (P = 0.021) and 10 months (P = 0.019).

Our finding of no change in NEPA in response to aerobic exercise training is in agreement with the results of several short-term studies (range, 2–16 d) (19,20,36) and randomized trials (range, 13–32 wk) (3,28,29). However, significantly increased NEPA has been reported 48 h after completing 60 min of high-intensity interval treadmill walking (5 min at 6 km·h−1, 10% grade; 5 min at 6 km·h−1, 0% grade) in a sample of overweight and obese, sedentary, young adult men (2). Significantly decreased NEPA has been reported in two 12-wk nonrandomized trials in overweight, older men and women (22,23). Both of these trials included a resistance training component in addition to aerobic exercise. Interestingly, several studies have demonstrated disagreement between NEPA and NEEx results within the same study. For example, Meijer et al. (24) found no effect of aerobic exercise training on NEPA assessed by an accelerometer in a sample of men (n = 16) and women (n = 16) but found a significant increase in NEEx assessed by DLW in a subsample (n = 4 men, n = 4 women), as previously described. Colley et al. (4) also reported a discrepancy between NEPA assessed by an accelerometer and NEEx assessed by DLW in a small sample (n = 7) of overweight/obese women in response to a 4-wk moderate-intensity walking program (goal of 1500 kcal·wk−1). NEPA was unchanged, whereas NEEx decreased significantly from baseline to week 4. Potential discrepancies between assessments of NEEx and NEPA argue for the use of DLW-assessed NEEx when trying to evaluate the effect of exercise in the context of weight management.

Response to increased EEEx

Our observation of no significant difference for change in either NEEx or NEPA in response to increased levels of EEEx (400 or 600 kcal per session) is in agreement with other reports in the literature. For example, results from short-term trials over 7 d (31,32), which assessed NEEx using HR monitoring with individual HR/energy expenditure calibration, and 14 d (40) with NEEx assessed by DLW, have both shown no difference for change in NEEx with increased levels of EEEx. Hollowell et al. (16), in an 8-month trial, found no between-group differences for change in NEEx assessed by an accelerometer for participants randomized to nonexercise control or aerobic exercise at 5023 or 8272 kJ·wk−1. Church et al. (3) reported no significant between-group difference for change in NEPA, assessed by a pedometer, in a sample of older, overweight/obese women who completed a 6-month exercise intervention at energy expenditures of 4, 8, or 12 kcal·kg−1·wk−1. In a sample of overweight/obese young adult men (age, approximately 30 yr), Rosenkilde et al. (29) reported no significant difference for change in NEPA, assessed by an accelerometer, between men who completed an aerobic exercise intervention (3 d·wk−1) at either 300 or 600 kcal per session. Although not statistically significant, NEPA was increased 37% (P = 0.09) in the 300-kcal-per-session versus that in controls (29).

Individual variability

Although we observed no significant mean change, there was a considerable interindividual variability in the NEEx and NEPA responses to aerobic exercise training. Reductions in both NEEx and NEPA were seen in approximately 50% of participants in the exercise groups. Interindividual variability in the response of both NEEx and energy intake to exercise contributes to the high levels of interindividual variability in the weight change response to aerobic exercise training (7,25). The identification of both participant characteristics (e.g., age, sex, weight, race/ethnicity, aerobic capacity) and characteristics of the exercise intervention (e.g., mode, frequency, intensity, duration, time of day, level of EEEx) associated with decreased NEPA and NEEx in response to aerobic exercise training will be important for the development of targeted effective weight management interventions involving exercise alone or exercise combined with energy restriction.

TDEE

In this study, TDEE was significantly increased in the 600-kcal-per-session groups but not in the 400-kcal-per-session group (Fig. 1). TDEE increased even with weight loss over the 10-month intervention of −3.9 kg (−4.3%) in the 400-kcal group and −5.2 kg (−5.7%) in the 600-kcal group (9). The increased TDEE observed in both exercise groups also occurred despite small decreases in RMR in both groups and small changes in NEEx and reflected the increased daily EEEx when averaged over the 14-d DLW study period (400 kcal per session, 208 kcal·d−1; 600 kcal per session, 324 kcal·d−1). Previous studies where TDEE was assessed by DLW have reported both increased (24,40) or no change (4,13) in TDEE in response to aerobic exercise. Previous studies were completed over both short (14-d (40)) and longer durations (8 (4,13) to 20 wk (24)) in generally small samples (range, 8–13 participants per study) of both normal-weight (13,24,40) and overweight/obese individuals (4). We are unaware of other longer-term trials that have investigated the effect of increased EEEx on TDEE.

Sex differences

We observed potentially interesting sex differences for both change in TDEE and NEEx in response to increased EEEx (Fig. 1). In women, the change in TDEE in both the 400- and 600-kcal-per-session groups was greater than that in men in both the 400- and 600-kcal-per-session groups. The difference for change in TDEE was explained, at least in part, by the larger changes in both RMR and NEEx in men compared with those in women. The literature on sex differences in the responses of TDEE, NEEx, or NEPA to aerobic exercise training is limited. Fujita et al. (12) reported an increase in TDEE in response to a 25-wk exercise intervention (three 2-h supervised exercise classes per week) in a sample of older women (approximately 67 yr) but not in men. Stubbs et al. (31,32) conducted two short-term crossover studies using nearly identical exercise protocols (control vs two levels of cycle ergometer exercise) and assessments of NEEx (HR monitoring) in small samples of normal-weight men (n = 6) (31) and women (n = 6) (32). TDEE increased significantly with increased EEEx, with no significant differences in NEEx between exercise conditions and control. However, NEEx decreased significantly over the 7-d protocol in men but not in women (31,32).

Strengths and limitations

Strengths of the current study include the use of a randomized efficacy design with an intervention over 10 months that supervised exercise with two levels of EEEx, with verification of EEEx and assessment of RMR by indirect calorimetry, TDEE measured by DLW, a relatively large sample compared with that in the limited available literature, inclusion of both men and women, and the inclusion of measures of both NEEx and NEPA. However, as previously described, MET-2 was not specifically designed or powered to detect between- or within-group or sex differences in the response of NEEx or NEPA to aerobic exercise training. In addition, NEEx was assessed only at baseline and the end of the study, which precluded any assessment of the time course of change in NEEx over the course of the 10-month intervention.

SUMMARY

We found no significant change in mean NEEx or NEPA in a sample of initially sedentary, overweight, and obese young adults in response to 5 d·wk−1 of aerobic exercise intervention (400 or 600 kcal per session) over 10 months. However, there was a considerable interindividual variability in the NEEx and NEPA response. The change in NEEx and NEPA did not differ significantly by the level of EEEx; however, both NEEx and NEPA tended to increase with increased EEEx. The observation of an increase in TDEE in both the 400- and 600-kcal-per-session groups that was greater in women than that in men is interesting and warrants confirmation from an adequately powered trial. Our results, and those from the limited available literature (one short-term and three nonrandomized trials), suggest the need for additional randomized trials using state-of-the art assessment techniques. Trials should be designed and powered to determine the effect of intervention factors including exercise mode, frequency, level of EEEx, intermittent versus continuous exercise, exercise time of day, and participant factors including age, sex, race/ethnicity, body weight, and aerobic capacity on both TDEE and NEEx. This information will be important in designing targeted interventions using exercise alone or exercise in combination with energy restriction for weight management.

This study was supported by the National Institutes of Health, grant R01-DK049181.

The authors report no conflict of interest.

The results of the present study do not constitute endorsement by the American College of Sports Medicine.

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Keywords:

COMPENSATION; EXERCISE; DOUBLY LABELED WATER; ACCELEROMETER; OBESITY

© 2014 American College of Sports Medicine