Abstract
Objectives
Increasing the reinforcing value of a stimulus occurs after repeated exposures to the reinforcer via neuroadaptations that increase the incentive salience of the stimulus. Exercise is a reinforcer and increasing exercise reinforcement (RRVex) may be dependent on simultaneously increasing tolerance for exercise intensity. Positive outcome expectancy (POE) of participating in an intervention can be an important determinant of treatment efficacy, such as when attempting to increase tolerance for exercise intensity or RRVex. We hypothesized that (1) high-intensity interval training (HIIT) that produces great discomfort would increase tolerance for exercise intensity, (2) adding a positive outcome expectancy (POE) component to HIIT would further increase tolerance for exercise intensity and, (3) increases in tolerance for exercise discomfort would mediate increases in RRVex.
Methods
A randomized controlled trial with a factorial design included HIIT + POE (n = 33 adults, n = 19 women) and HIIT-only (n = 33, n = 19 women) groups. Both groups participated in HIIT 3 d/wk for 6 wks. HIIT + POE received POE treatment each exercise session. Outcomes were measured at baseline, after 6 weeks of HIIT, and 4 weeks post-HIIT (10 wk). Changes in the RRVex were assessed by a progressive ratio schedule of reinforcement task. Other outcomes were outcome expectations, tolerance for exercise intensity, and behavior regulations of exercise.
Results
Outcome expectancy did not change in either group. Tolerance for exercise discomfort increased (P < .001) above baseline by 12% at 6 wk and 13% at 10 wk. Intrinsic, integrated, and identified behavior regulations of exercise were all increased (P < .01) at 6 wk and remained so at 10 wk. However, RRVex was not changed and change in RRVex was not correlated with change in tolerance for exercise intensity.
Conclusions
HIIT increases tolerance for exercise intensity and intrinsic, integrated, and identified behavior regulations of exercise.
Funding Sources
USDA-ARS.