Date Published: May 7, 2019
Publisher: Public Library of Science
Author(s): Kyle D. Flack, Kelsey Elise Ufholz, LuAnn Johnson, James N. Roemmich, Maciej S. Buchowski.
Increasing exercise reinforcement, or decreasing sedentary reinforcement, may reduce sedentary activity and promote habitual exercise. Repeated exposures to a reinforcer may increase its reinforcing value (i.e., incentive sensitization). It is not yet known whether incentive sensitization occurs for exercise or factors associated with incentive sensitization for exercise reinforcement. The purpose was to determine whether exercise exposures increase exercise reinforcement relative to a sedentary alternative and whether this sensitization of exercise reinforcement would alter physical or sedentary behavior. This work also determined whether exercise dose, intensity, and preference and tolerance for exercise intensity were associated with incentive sensitization of exercise.
104 sedentary men and women were randomized to exercise training groups with 89 completing the study. Groups included exercise exposures of 150 (n = 35) or 300 kcal/session (n = 34), 3 sessions/week for 6 weeks, or a non-exercise control group (n = 35). Assessments for exercise and sedentary behavior reinforcement (primary dependent variables) and activity and tolerance for exercise intensity were performed at baseline (week 0), post training (week 6), and post washout (week 10).
The control group reduced (P = 0.022) relative reinforcing value of exercise, such that the 150 kcal group had a greater relative reinforcing value of exercise after the exercise treatment 150 kcal: 0.69 ± 0.07 to 0.74 ± 0.07; 300 kcal: 0.72 ± 0.07 to 0.63 ± 0.08, control: 0.72 ± 0.07 to 0.57 ± 0.08 mean ± SE. Increases in tolerance for exercise intensity discomfort were associated with increases in relative reinforcing value of exercise. Sedentary behavior reinforcement decreased in both exercise groups (150 kcal: 5.4 ± 4.3 to 1.8 ± 1.3; 300 kcal: 5.4 ± 4.3 to 3.1 ± 2.4, P<0.05), but remained unchanged in the control group (5.1 ± 4.0 to 6.1 ± 4.9, P>0.05). Sedentary activity decreased baseline to post-training in the 300 kcal group (546.5 ± 10.7 to 503.8 ± 11.8 minutes, P<0.01). Small amounts of regular exercise may reduce the reinforcing value sedentary behavior. The process of incentive sensitization of exercise may include reducing the reinforcing value of competing sedentary activities. Developing tolerance to exercise discomfort of exercise may be critical to increasing exercise reinforcement.
The CDC Physical Activity Guidelines for Americans and their inclusion in the Dietary Guidelines for Americans (DGA) provide evidence-based advice to promote health and to reduce risk for chronic diseases through physical activity (PA) [1, 2]. However, only one in four Americans report engaging in any leisure time PA . The low adherence of most Americans to PA recommendations underscores the need to understand how to effectively make PA a habit. An ideal product would be exercise programs that simultaneously increase both fitness and the motivating value of being physically active, such that initiation of a regular exercise regimen also promotes long-term PA adherence.
During the intervention, participants in the 300 kcal group expended 335.6 ± 5.7 kcal per session whereas the 150 kcal group expended 182.0 ± 6.3 kcal (mean ± standard error, SE). The group by time interaction for Pmaxexercise was not significant (p = 0.23). Pmaxexercise decreased (P<0.0001) from baseline to post-training (6 weeks, P<0.0001) and from baseline to post-washout (10 weeks, P = 0.011). Simple effects analyses (Fig 2) showed that Pmaxexercise decreased (P = 0.013) from baseline to post-training in the 300 kcal group; and from baseline to post-training (P = 0.0004) and baseline to post-washout (P = 0.015) in the control group. There was a significant group by time interaction (P = 0.047) for Pmaxsed (Fig 2). Pmaxsed decreased in the 150 kcal group between baseline and post-training (6 weeks, P = 0.003) and between baseline and post-washout (10 weeks, p<0.0001), while the 300 kcal group decreased (p = 0.049) between baseline and post-washout. No changes were observed (P = 0.31) in the control group. The rate of change in Pmaxsed was negative (P≤0.048) from baseline to post-washout (10 weeks) for both exercise groups. Based on the changes in Pmaxexercise and Pmaxsed the treatment by phase interaction for RRVexercise was P = 0.066. Examination of the simple effects analyses was informative as the control group reduced (P = 0.022) RRVexercise between baseline and post-training (6 weeks) and the 150 kcal group had a greater RRVexercise at the post-training (P = 0.035) and the post-washout (10 weeks, P = 0.018) phases compared to the control group (Fig 2). A treatment effect was observed (P = 0.048) for RRVexercise in that the 150 kcal group had a greater (P = 0.037) RRVexercise than the control group. Covarying for BMI or age did not influence the results presented above for Pmaxexercise, Pmaxsed, and RRVexercise. The average MET intensity of exercise during the exposure sessions did not moderate (P≥0.26) the association of change in tolerance for exercise discomfort on change in RRVexercise. The present study is the first RCT aimed at investigating whether a low-dose exercise program (i.e., below recommended minutes per week) could induce incentive sensitization of exercise reinforcement among adults who were engaging in no more than one day of exercise per week. Though there were no specific entry criteria for sedentary behavior, baseline accelerometer sedentary behavior of all the study groups exceeded usual adult values . The present study also assessed whether factors including the self-selected intensity of the exercise sessions (exposures) and the change in tolerance to exercise intensity discomfort were associated with the incentive sensitization of exercise reinforcement. The exercise parameters in the present study were not prescribed to promote health and fitness, but rather to investigate whether a low-dose of exercise could promote incentive sensitization for exercise reinforcement. It may be beneficial for novice exercisers to begin exercise programs that focus on increasing exercise reinforcement and exercise as a habit before focusing on fitness and health. The low doses of exercise used in the present study were enough to decrease sedentary behavior reinforcement and shift choice away from sedentary behaviors, which helped to maintain RRVexercise during and after the exercise treatment. The current longitudinal results provide extend cross-sectional evidence that increasing the preference and tolerance to exercise intensity may be important for increasing RRVexercise, and exercise intensity is a key component in increasing preference and tolerance for exercise intensity. Perhaps the low dose of exercise in the current study would have been able to induce incentive sensitization if the intensity of the exercise completed at each session was very great, such as occurs with high-intensity interval training. Source: http://doi.org/10.1371/journal.pone.0216355