Abstract

Epidemiological studies consistently report that physical activity is inversely related to substance use and abuse. Similar to many abused substances, physical activity produces positive affective states in both humans and animals. These positive affective states can be measured objectively and quantitatively, and have been demonstrated under a variety of experimental conditions (Belke & Wagner, 2005; Greenwood et al., 2011; Janal, Colt, Clark, & Glusman, 1984; Lett, Grant, Byrne, & Koh, 2000; Lett, Grant, & Koh, 2001; Nabetani & Tokunaga, 2001). Exercise also functions as a positive reinforcer, in that both humans and animals will perform an operant response (e.g., drive to a gym, press a lever) in order to engage in physical activity (Belke, 1997, 2000; Belke & Dunbar, 2001; Iversen, 1993; Schebendach, Klein, Foltin, Devlin, & Walsh, 2007). Preclinical studies report that aerobic exercise decreases drug self-administration and other measures of drug-seeking behavior. For instance, in laboratory rats, access to a running wheel decreases the acquisition (Smith & Pitts, 2011), maintenance (Cosgrove, Hunter, & Carroll, 2002; Smith, Schmidt, Iordanou, & Mustroph, 2008), and escalation (Smith, Walker, Cole, & Lang, 2011) of cocaine self-administration, and decreases the reinstatement of cocaine-seeking behavior after a period of abstinence (Lynch, Piehl, Acosta, Peterson, & Hemby, 2010; Smith, Pennock, & Walker, 2011; Zlebnik, Anker, Gliddon, & Carroll, 2010). Similar effects have been reported with other drugs of abuse, including alcohol (Crews, Nixon, & Wilkie, 2004; Ehringer, Hoft, & Zunhammer, 2009, but see Werme, Lindholm, Thorén, Franck, & Brené, 2002; McMillan, McClure, & Hardwick, 1995; Ozburn, Harris, & Blednov, 2008), morphine (Hosseini, Alaei, Naderi, Sharifi, & Zahed, 2009), and methamphetamine (Miller et al., 2011). A number of behavioral/psychological mechanisms likely contribute to the beneficial effects of exercise on drug-seeking behavior. For instance, exercise decreases several comorbid psychological conditions that are associated with substance abuse and dependence. Specifically, exercise decreases measures of depression and anxiety (see reviews by Herring, O'Connor, & Dishman, 2010; Perraton, Kumar, & Machotka, 2010), both of which are risk factors for developing a substance use disorder (Castle, 2008; Swendsen & Merikangas, 2000). Exercise also reliably increases measures of well-being, self-esteem, and self-efficacy (Fillipas, Oldmeadow, Bailey, & Cherry, 2006; Hughes et al., 2010; Muller et al., 2008). These positive psychological states are negatively correlated with substance use (Ellickson & Hays, 1991; Griffin, Scheier, Botvin, & Diaz, 2001; Zamboanga, Schwartz, Jarvis, & Van Tyne, 2009), and may offer protection against developing a substance use disorder. In addition to these mechanisms, exercise also produces functional adaptations in the central nervous system that may leave an individual less susceptible to developing compulsive patterns of drug intake. Although research into this latter area is still in its infancy, a growing number of studies reveal that many signaling molecules that mediate drug-seeking behavior are modulated by physical activity.