The Impact of Timing of Exercise Initiation on Weight Loss: An 18-Month Randomized Clinical Trial

Abstract

Objective: This study aimed to evaluate the impact of timing of exercise initiation on weight loss within a behavioral weight loss program.

Methods: Adults with overweight or obesity (N = 170; age 18-55 years; BMI 25-42 kg/m2 ; 83.5% women) were enrolled in an 18-month behavioral weight loss program consisting of a reduced-calorie diet, exercise, and group-based support. The standard group (STD) received a supervised exercise program (progressing to 300 min/wk of moderate-intensity aerobic exercise) during months 0 to 6. The sequential group (SEQ) was asked to refrain from changing exercise during months 0 to 6 and received the supervised exercise program during months 7 to 12. On completion of supervised exercise, both groups were instructed to continue 300 min/wk of moderate-intensity exercise for the study duration.

Results: At 6 months, the STD group exhibited greater reductions in body weight (-8.7 ± 0.7 kg) compared with the SEQ group (-6.9 ± 0.6 kg; P = 0.047). Between 6 and 18 months, the STD group regained more weight (2.5 ± 0.8 kg vs. 0.0 ± 0.8 kg; P = 0.02). At 18 months, there were no between-group differences in changes in weight (STD: -6.9 ± 1.2 kg; SEQ: -7.9 ± 1.2 kg), fat mass, lean mass, physical activity, or attrition.

Conclusions: Both immediate and delayed exercise initiation within a behavioral weight loss program resulted in clinically meaningful weight loss at 18 months. Thus, timing of exercise initiation can be personalized based on patient preference.

Trial registration: ClinicalTrials.gov NCT01985568.

© 2019 The Obesity Society.

Figures

Figure 1:

Study Consort Diagram

Figure 2:. Changes in Weight, Waist Circumference, Fat Mass, and Lean Mass by Randomized Group a

a Results (mean ± SEM) are from linear mixed effect model with unstructured covariance using an intent-to-treat analysis; Statistically significant P values (P <0.05) are indicated in bold; SEQ: Sequential; STD: Standard. * indicates p

Figure 3:. Changes in Physical Activity, Fitness by Randomized Group a-c

a Results (mean ± SEM) are from linear mixed effect model with unstructured covariance using an intent-to-treat analysis; Statistically significant P values (P <0.05) are indicated in bold; Bout MVPA: bouts of ≥10 minutes in duration of moderate-to-vigorous physical activity (≥3.00 METs); Non-bout MVPA: any minute ≥3 METs that did not meet the definition for bout MVPA; Total MVPA: any minute ≥3 METs; SEQ: Sequential; STD: Standard; VO2max: maximal aerobic capacity. b Sample sizes for bouts ≥10 minutes of MVPA, non-bout MVPA, total MVPA, and Steps are: STD: n=74 at 0M, n=63 at 6M, n=56 at 12M, n=54 at 18M; SEQ: n=81 at 0M, n=67 at 6M, n=55 at 12M, n=49 at 18M. c Sample sizes for VO2max are: STD: n=85 at 0M, n=67 at 6M, n=57 at 12M, n=50 at 18M; SEQ: n=85 at 0M, n=73 at 6M, n=58 at 12M, n=51 at 18M. * indicates p** indicates p<0.01 for the differences of STD – SEQ in change in the parameter from baseline.

Figure 4:. Changes in Exercise Perceptions by Randomized Group a-e

a Results (mean ± SEM) are from linear mixed effect model with unstructured covariance using an intent-to-treat analysis; Statistically significant P values (P <0.05) are indicated in bold; SEQ: Sequential; STD: Standard. b Sample sizes for Exercise Enjoyment are: STD: n=84 at 0M, n=67 at 6M, n=61 at 12M, n=60 at 18M; SEQ: n=85 at 0M, n=74 at 6M, n=63 at 12M, n=59 at 18M; measured with the modified Physical Activity Enjoyment Scale (PACES); scale is 1 to 5. c Sample sizes for Exercise Self-Efficacy are: STD: n=84 at 0M, n=67 at 6M, n=61 at 12M, n=60 at 18M; SEQ: n=85 at 0M, n=73 at 6M, n=63 at 12M, n=59 at 18M; measured with the Barriers Self-Efficacy Scale (BARSE); scale is 1 to 10. d Sample sizes for Exercise Benefits are: STD: n=84 at 0M, n=67 at 6M, n=60 at 12M, n=59 at 18M; SEQ: n=85 at 0M, n=73 at 6M, n=62 at 12M, n=59 at 18M; measured with the Exercise Benefits and Barriers Scale (EBBS); scale is 29 to 116. e Sample sizes for Exercise Barriers are: STD: n=82 at 0M, n=67 at 6M, n=61 at 12M, n=60 at 18M; SEQ: n=83 at 0M, n=73 at 6M, n=62 at 12M, n=59 at 18M; measured with the Exercise Benefits and Barriers Scale (EBBS); scale is 14 to 56. * indicates p** indicates p<0.01 for the differences of STD – SEQ in change in the parameter from baseline.

Figure 5:. Survival Proportions for Exercise-Related Adverse Events by Randomized Group a-c

a Results from Kaplan-Meier analysis, where survival was censored (tick marks) by either withdrawal week or at week 78 for completers; Statistically significant P values (P <0.05) are indicated in bold; The first dotted line indicates the month 6 mark; The second dotted line indicates the month 12 mark; SEQ: Sequential; STD: Standard. b Of the total exercise-related adverse events (n=28), 89% were musculoskeletal (11 knee pain, 3 back pain, 3 foot pain, 2 hip pain, 2 plantar fasciitis, 2 foot/ankle sprain, 1 calf pain, 1 meniscus tear) and 11% were cardiopulmonary (2 instances of shortness of breath due to asthma, 1 instance of palpitations due to premature ventricular contractions). c Of the total exercise-related adverse events (n=28), 43% were determined to be due to an acute injury, while the remainder were determined to be an overuse injury and/or exacerbation of a pre-existing condition.

Figure 6:. Changes in Dietary Behaviors by Randomized Group a-e

a Results (mean ± SEM) are from linear mixed effect model with unstructured covariance using an intent-to-treat analysis; Statistically significant P values (P <0.05) are indicated in bold; SEQ: Sequential; STD: Standard. b Sample sizes for Restraint are: STD: n=84 at 0M, n=65 at 6M, n=61 at 12M, n=59 at 18M; SEQ: n=84 at 0M, n=74 at 6M, n=61 at 12M, n=59 at 18M; scale is 0 to 21. c Sample sizes for Disinhibition are: STD: n=83 at 0M, n=65 at 6M, n=60 at 12M, n=59 at 18M; SEQ: n=83 at 0M, n=74 at 6M, n=61 at 12M, n=59 at 18M; scale is 0 to 16. d Sample sizes for Hunger are: STD: n=83 at 0M, n=65 at 6M, n=61 at 12M, n=59 at 18M; SEQ: n=85 at 0M, n=74 at 6M, n=61 at 12M, n=59 at 18M; scale is 0 to 14. e Sample sizes for Diet Self-Efficacy are: STD: n=83 at 0M, n=66 at 6M, n=60 at 12M, n=59 at 18M; SEQ: n=84 at 0M, n=73 at 6M, n=63 at 12M, n=58 at 18M; scale is 0 to 180. * indicates p** indicates p<0.01 for the differences of STD – SEQ in change in the parameter from baseline.