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COPYRIGHT 2006 University of South Alabama
For more than 30 years researchers have been touting the feel-better effects of aerobic exercise (e.g., Morgan, Roberts, & Feinerman, 1971; Thayer, Newman, & McClain, 1994; Yeung, 1996). To date, the mechanisms which underlie these positive changes in affective state are not understood (Landers & Arent, 2001). Unfortunately though numerous hypotheses have been forwarded, most research examining the "feel-good" phenomenon to date has been descriptive in nature as opposed to theoretical (Ekkekakis, Hall, & Petruzzello, 1999). For instance, researchers have examined the distraction hypothesis (Bahrke & Morgan, 1978; Morgan, 1985), the monoamine hypothesis (Chaouloff, 1989; Morgan, 1985), the cerebral lateralization hypothesis (Hatfield & Landers, 1987), and the endogenous opioid hypothesis (Janal, Colt, Clark, & Glusman, 1984). In addition to these hypotheses, one theoretical model that has generated interest is Solomon's opponent-process model of acquired motivation (Solomon, 1980; Solomon & Corbit, 1974).
Solomon's theory (1980) proposes that the brain is organized to maintain homeostasis and oppose extreme emotional processes (e.g., pleasure or pain). This is accomplished through two 'opponent' processes that occur as a result homeostasis disruption. For instance when a stimulus is encountered, the organism responds to minimize the impact of the stimulus through the elicitation of two processes, the a and b. The a process responds immediately, in proportion to the stimulus, and returns to resting levels when the stimulus is no longer present. The opponent or b process is slower acting, responds in proportion to the a process, and gradually returns to resting levels when the stimulus is no longer present. The summation of the a and b process leads to the emergent response of the overall system. A key component of Solomon's theory (1980) relates to repeated exposure to a stimulus. With repeated exposure, the a process remains relatively constant in its reaction while the b process becomes stronger in its reaction. Thus, over time the stimulus will have less of an effect on the emergent state of the system during engagement and a larger effect on the system when the stimulus is disengaged.
In the context of exercise, the opponent-process theory would predict that individuals feel worse during and better following the exercise session. This prediction has been supported in parts given the vast amount of research that has demonstrated an improvement of mood following exercise (e.g., Bahrke & Morgan, 1978; Bixby et al., 2001; Lochbaum, Karoly, & Landers, 2004) and worsening of mood during exercise (Bixby, Spalding, & Hatfield, 2001, Hall, Ekkekakis, & Petruzzello, 2002; Lochbaum et al., 2004). Even with all of this supportive evidence, few researchers have mentioned Solomon's theory as a potential explanation for their results (Blanchard, Rodgers, Spence, & Courneya, 2001; Boutcher & Landers, 1988) and only a few researchers have specifically investigated the opponent-process theory (Bixby et al., 2001; Lochbaum et al., 2004; Petruzzello, Jones, & Tate, 1997).
The support for Solomon's theory has been mixed (Lochbaum et al., 2004). Lochbaum and colleagues (2004) noted several serious methodological weaknesses in past research that has limited conclusions concerning the viability of Solomon's theory as an explanation for the affective reactions of participants to exercise. These weaknesses included the failure for adequate measuring of affect across the entire exercise experience (Blanchard et al., 2001; Boutcher & Landers, 1988) and the lack of distinct aerobic fitness or exercise history differences between participant groups (Bixby et al., 2001; Petruzzello et al., 1997). In their attempt to replicate and extend past research examining Solomon's theory (1980), Lochbaum and colleagues (2004) reported that their results generally failed to support Solomon's notion of an opponent reaction. The authors themselves noted that their post exercise time point measurement was somewhat limited and that the exercise intensity calculation from a fixed percent of maximal oxygen consumption might have lead to differing metabolic requirements across all of the participants. More recent research has demonstrated that exercise prescription should be based on percent of ventilatory threshold (Bixby et al., 2001; Hall et al., 2002). In addition, Lochbaum and colleagues (2004) failed to measure ratings of perceived exertion to verify whether or not differences existed within or between...
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