ORIGINAL ARTICLE The Impact of Incentives on Exercise Behavior: A Systematic Review of Randomized Controlled Trials Kelley Strohacker, Ph.D. & Omar Galarraga, Ph.D. & David M. Williams, Ph.D. Published online: 5 December 2013 # The Society of Behavioral Medicine 2013 Abstract Background The effectiveness of reinforcing exercise behav- ior with material incentives is unclear. Purpose This study aims to conduct a systematic review of existing research on material incentives for exercise, orga- nized by incentive strategy. Methods Ten studies conducted between January 1965 and June 2013 assessed the impact of incentivizing exercise com- pared to a non-incentivized control. Results There was significant heterogeneity between studies regarding reinforcement procedures and outcomes. Incentives tended to improve behavior during the intervention while findings were mixed regarding sustained behavior after incen- tives were removed. Conclusions The most effective incentive procedure is un- clear given the limitations of existing research. The effective- ness of various incentive procedures in promoting initial be- havior change and habit formation, as well as the use of sustainable incentive procedures should be explored in future research. Keywords Reinforcement . Incentive . Operant conditioning theory . Physical activity Introduction A substantial body of literature indicates that physical inac- tivity is common and widespread [1–3], contributes to a variety of disease states, such as cardiovascular disease and type 2 diabetes [4, 5], and places undue economic burden on healthcare systems [6, 7]. Therefore, research focused on how best to improve and maintain adequate levels of physical activity is a high priority. One avenue of exploration is the use of incentives based on operant conditioning and behavioral economics principles. In operant conditioning theory, an incentive is a stimulus that is presented contingent on performance of a specified behavior for the purposes of increasing the frequency of the behavior [8]. Reinforcements can be positive (i.e., presentation of a stimulus in response to behavior) or negative (i.e., removing a stimulus in response to behavior) [8]. Additionally, rein- forcement schedules are determined by timing of behavioral consequences [8]. Ratio schedules provide reinforcement after the behavior has been performed a predetermined number of times. Interval schedules provide reinforcement following a predetermined period of time since the previous reinforce- ment, if the behavior is performed during that period of time. Reinforcement schedules can also be fixed or variable. Principles of behavioral economics, such as present bias, anticipated regret, and loss aversion have been used in con- junction with operant conditioning theory as a way to “nudge” people into adopting behaviors that they normally want to achieve, but cannot because of human tendency for departure from fully “rational” behavior [9, 10]. For example, according to the principle of present bias, financial incentives may provide motivation for exercise by providing an immediate payoff in contrast to delayed health-related benefits of exer- cise [11–14]. Likewise, anticipation of regret for missing out on a potentially large financial payoff may lead people to participate in lottery systems in which lottery chances are K. Strohacker (*) Department of Kinesiology, Recreation and Sport Studies, The University of Tennessee, 1914 Andy Holt Ave., 322 HPER Bldg, Knoxville, TN 37996-2700, USA e-mail: kstrohac@utk.edu O. Galarraga Department of Health Services, Policy & Practice, Brown University School of Public Health, Providence, RI, USA D. M. Williams Department of Behavioral and Social Sciences, Brown University School of Public Health, Providence, RI, USA ann. behav. med. (2014) 48:92–99 DOI 10.1007/s12160-013-9577-4