Investigation of the reward value of exercise
Abstract
Exercise is an important health behavior. Expressed reasons for participation are often delayed outcomes i.e. health threats and benefits, but also can be immediate like enjoyment. However, it was not known how people evaluate exercise as a reward. The value of rewards diminishes with delays, and the delay discounting effect can undermine decision-making. Delay discounting (assessed by discounting rate -k value) is defined as the decline in the subjective value of a reward with delay to its receipt. Exercise subjective reward valuation is a principal step in decision making. However, apart from the decision to participate in exercise, further decisions regarding specific parameters need to be made. The selection of exercise intensity might be influenced by visceral factors and motives related to goals, but the principal evaluation of exercise per se is yet to be explored. The general aim of this thesis was to investigate the delay discounting of exercise in comparison with food and money in healthy adults. It also aimed to investigate whether body characteristics, physical activity, and selected physiological and psychometric measures were associated with k values. In chapter 2, based on the above aims, self-paced exercise sessions on treadmill were conducted and the k values of exercise were compared with those of food and money. The outcomes show that young, moderately active participants (n=70) preferred walking/running intensity with low to moderate cardiovascular strain and light perceived exertion. k values indicated that exercise was discounted like consumable rewards as food and more rapidly than monetary rewards. Significant associations were detected of exercise k value with preferred speed and with extrinsic exercise motivation. High intensity exercise training (n=16) reduced exercise k values specifically and exercise k value was quicker in individuals who preferred lower speeds being less physically active. In chapter 3, the objectives were to investigate whether the visceral reward and self-selection of exercise are modifiable in connection to the exercise physiological strain through high intensity interval training. To accomplish this target,
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exercise training and evaluative conditioning (EC) were combined. Using a randomized control design (N=58). Pre, post three weeks interval training w/o conditioning, and after 4 weeks follow-up, participants were tested on self-paced speed selection on treadmill, delay discounting of exercise and food rewards. Outcomes revealed that delay discounting of self- paced exercise was specifically influenced by training but not by EC. However, selection of intensity was significantly increased by EC and physiological adaptation to training, revealing the importance of visceral factors. In agreement with effort discounting models, the choice for a self-selected intensity depended on the acutely perceived pleasantness of exercise, discounted against perceived effort. This suggests a separation of decision-making processes for the evaluation of exercise, based on cognitive processes, and intensity selection of self-paced exercise, based on rewarding visceral experience of physical strain. In chapter 4, an online survey was conducted to investigate the reward value of un-specific exercise experience to enable a wider spectrum of ecological and psychological characteristics with integrating aspects of passive sports consumption related screen time and reward preference. A cross sectional design through a Qualtrics online survey have been used to recruit 200 participants on Amazon’s Mechanical Turk. Results show that un-specific exercise experience was found to be discounted as established rewards. Significant negative associations were detected of exercise discounting rates with extrinsic exercise motivation, physical activity levels, and positive association with sports-screen tim