Increasing Discomfort Tolerance Predicts Incentive Sensitization of Exercise Reinforcement: Preliminary Results from a Randomized Controlled Intervention to Increase the Reinforcing Value of Exercise in Adults
Authors: Roemmich James N. , Flack Kyle , Johnson LuAnn , Ufholz Kelsey 
Published: June 2021

BackgroundThe reinforcing (motivating) value of exercise relative to sedentary behavior (RRVex) predicts usual exercise behavior and meeting of physical activity guidelines. Recent cross‐sectional evidence suggests, for the first time, that greater tolerance for the discomfort experienced during exercise is associated with greater RRVex. But, it is not known whether discomfort tolerance or RRVex can be increased.ObjectiveThe primary aim of this randomized controlled trial is to determine whether the RRVex is increased after repeated exposures to exercise (i.e., incentive sensitization). The primary hypothesis is engaging in 300 kcal bouts of exercise will increase RRVex more than 150 kcal bouts and a no exercise control. A second aryhypothesis is increases in discomfort tolerance will be positively associated with the increase in RRVex.MethodsPreliminary results are from 56 adults who participated in a3‐arm, randomized, controlled, community‐based, 6‐wk exercise intervention. For the exercise arm treatments, participants engage in either 300 kcal or 150 kcalbouts of exercise 3 days/wk. For the control arm, participants receive no active intervention, but attend the same number of assessment visits. Outcomes are tested at baseline, after 6 weeks of treatment, and 4 weeks after treatment(10 weeks). RRVex is assessed via an operant responding task that uses in dependent progressive ratio schedules of reinforcement to earn time for exercise (e.g., treadmill, elliptical) or sedentary (e.g. TV, magazines)behavior. The RRVex is calculated as the number of sessions completed for access to exercise/(sessions completed for exercise + sedentary). Discomfort tolerance is measured via the Preference for and Tolerance of the Intensity of Exercise Questionnaire. Usual activity is measured via accelerometer. Differences in groups across time is tested using a mixed linear model with time as a within‐subject factor, treatment group as a between‐subjects factor and subject as a random effect.ResultsAt this preliminary analysis, there are no significant treatment or time effects for RRVex. The group × time interaction for discomfort tolerance is p = 0.08 with baseline to end of 6 weeks of exercise training changes of 10.1%, 4.6% and −7.6% for the 300 kcal, 150 kcal, and control groups, respectively. The baseline to 10 week change in usual minutes of moderate‐to‐vigorous physical activity is 31.0%, −5.8% and −17.6% for the 300 kcal, 150 kcal, and control groups, respectively Importantly, individual differences in the increase in discomfort tolerance during exercise predicts increases in RRVex at 6 (r = 0.33, p < 0.01) and 10 (r = 0.26, p = 0.06) weeks.ConclusionsThese data provide novel insights into an individual difference variable, tolerance for the discomfort experienced during exercise, that is changeable with repeated exercise exposures; and when increased may promote increases in RRVex. Future work will determine how to most effectively increase discomfort tolerance.Support or Funding InformationFunded by USDA‐ARS Project Plan 3062‐51000‐051‐00D