Behavioral reinforcement is driven mainly by the central dopamine system. Increasing the reinforcing value of a stimulus, termed “incentive sensitization”, originally proposed to explain drug addiction, has been applied to other reinforcing behaviors such as gambling and eating. Incentive sensitization occurs after repeated exposures by producing neuroadaptations that increase the craving or “wanting” of the stimulus. The extent to which exercise reinforcement can be increased is not yet known, although biologically plausible, as exercise can elicit dopaminergic responses similar to other reinforcing behaviors. The reinforcing value of exercise is associated with usual physical activity so increasing the reinforcing value of exercise should improve physical activity guideline adherence.
Changes in the reinforcing value of exercise and sedentary behaviors in sedentary adults were assessed by a progressive ratio schedule of reinforcement task in two separate exercise intervention studies differing in their frequency of exercise bouts (# of weekly sessions), total energy expended per session, and length of intervention. Other outcomes included the preference and tolerance for exercise intensity questionnaire.
Study 1 demonstrated no changes in exercise reinforcement and decreases in sedentary behavior reinforcement after 6-weeks of exercising at either 150 or 300 kcal per session, 3 times/week. In Study 2, exercise reinforcement increased when expending 600 kcal per session, 5 days/week, but not when expending 300 kcal, 5 days/week. Increases in tolerance for exercise intensity discomfort were associated with increases in the relative reinforcing value of exercise in both studies.
A large dose of exercise is needed to produce incentive sensitization of exercise reinforcement. Tolerance for exercise intensity is another factor that may influence this process.