It is common practice within the health-fitness domain to employ exercise prescription procedures that are based on the scientific evidence approved by national organizations such as the American College of Sports Medicine (ACSM) and the Centers for Disease Control and Prevention (CDC). PA guidelines have been proposed that define the intensity, duration, and frequency of an exercise program designed to elicit health-fitness benefits (ACSM 2013). Traditional exercise programs based on these guidelines set specific intensity prescriptions that target physiological ranges, often expressed as a %VO₂max, and thresholds such as the VT. It has been suggested that a target RPE can be used to self-regulate exercise intensity to produce optimal health-fitness training outcomes based on physiological criteria. Various methods have been employed to confirm the validity of exercise intensity self-regulation using target RPE’s, such as estimation–production paradigms for the assessment of prescription congruence and intensity discrimination.

However, prescribing exercise intensity based on guidelines that impose the intensity to be performed ignores an individual’s preference for and tolerance of certain exercise intensities. It has been shown that increases in exercise intensity are associated with decreases in affective responses (AR) (Ekkekakis and Petruzzello 1999). This decrease in the pleasure derived from exercise can lower adherence to the prescribed exercise program (Cox et al. 2003; Lee et al. 1996; Perri et al. 2002). Based on these results, many individuals may not benefit from an initial exercise prescription where an imposed exercise intensity is employed. The goal of an exercise program should not only be health-fitness benefits, but should also include the development of one’s willingness to participate in the activity. Therefore, one of the initial goals of an exercise prescription should be to promote program adherence. The adoption and maintenance of regular exercise will facilitate the ultimate goal of attaining the desired health-fitness benefits.

Prescribed exercise intensity can also be referred to as imposed exercise intensity. In this prescriptive scenario, the individual does not have a choice regarding the exercise intensity that he/she will perform. The imposition of exercise intensity can be seen by some individuals as highly controlling, negatively influencing AR and exercise adherence. Based on the theory of self-determination, engaging in an externally controlled behavior, such as performing imposed exercise intensity, decreases the intrinsic motivation to continue that behavior. Giving an individual the freedom to self-select the exercise intensity that will be performed may increase motivation for continued participation (Ryan and Deci 2000; Lind et al. 2008). Increased control over exercise intensity can lead to a greater enjoyment associated with exercise (Wankel 1993). This is important because of the positive link between exercise enjoyment and program adherence (Ryan and Deci 2000; Ryan et al. 1997; Caserta and Gillett 1998).

It has been proposed that a causal chain exists, linking (a) the intensity of PA (not only its level but whether it is self-selected or imposed), (b) AR to exercise (e.g., measured using Feeling Scale ratings), and (c) regular PA participation and/or adherence to exercise programming. Ekkekakis and Lind (2006) summarized the comparison between SS and imposed exercise intensity. They stated that during self-selected exercise, a sense of control is maintained such that the individual can avoid physical discomfort and fatigue. Therefore, self-selected exercise intensity may seem like a somewhat innocuous concept, negative emotions (e.g., social physique anxiety) may not arise, and a positive AR results. In contrast, when exercise intensity is imposed, personal control is taken away and overt signs of fatigue and discomfort may occur. The imposition of exercise intensity may be seen as posing a potential evaluative threat where negative emotions may arise, leading to decreased AR (Ekkekakis and Lind 2006). Studies have shown that imposed exercise intensities elicit a more negative (or comparatively less positive) AR when compared to self-selected exercise intensities (Ekkekakis and Lind 2006; Lind et al. 2008; Parfitt et al. 2000; Parfitt et al. 2006; Rose and Parfitt 2007).

It has been shown that for most individuals, self-selected exercise intensities are adequate to provide an overload training stimulus to promote gains in cardiorespiratory fitness while simultaneously providing a level of effort that results in a positive AR. Previous studies have found that, on average, self-selected exercise intensity is often similar to the VT or LT. Although many subjects chose self-selected intensity near the VT or LT, relatively few exceeded that level (Dishman et al. 1994; Ekkekakis and Lind 2006; Lind et al. 2005; Lind et al. 2008). Therefore, a prescription that employs self-selected exercise intensity may be beneficial for overall health-fitness without negatively affecting mood state or emotions.

RPE has been used to quantify the perception of exertional intensity during self-selected exercise. In a 20-min cycle ergometer exercise bout, both high- and low-active men estimated similar Borg Scale RPE’s at 5-min intervals. RPE increased from an average of 10.5 at minute 5 to an average of 14.2 at minute 20 (Dishman et al. 1994). In a 20-min bout of treadmill exercise in which speed was adjusted to produce self-selected intensity, previously sedentary middle-aged women estimated Borg RPE’s averaging approximately 11 at minute 5 and increasing to an average of almost 14 at minute 20 (Lind et al. 2005). Using the OMNI Scale during a 20-min bout of cycle ergometer exercise, college-aged males estimated RPE’s averaging 2 at minute 5 and increasing to an average of 5 at minute 20 (Haile et al. 2013). In each instance, subjects were allowed to adjust intensity every 5 min. In general, subjects increased intensity throughout the 20-min exercise bouts and, subsequently, RPE increased as well. On average, RPE’s measured during the later stages of the exercise bouts were within the perceived exertion range that encompasses the VT in most individuals, i.e., from 11 to 16 using the Borg Scale and from 5 to 7 using the OMNI Scale.

Parfitt and colleagues (2000) conducted an investigation in which RPE was compared between self-selected and imposed treadmill exercise in young adult males and females. Imposed exercise intensity was set at 65 % of VO₂max and subjects self-selected exercise intensity at 71 % VO₂max. Even though exercise intensity was significantly different between trials, RPE’s were similar. The exertion associated with the harder work rate during self-selected exercise intensity was perceived to be the same as for the lower, prescribed intensity. These findings indicate a potential positive perception of the self-selected exercise or conversely a negative perception of the imposed exercise (Parfitt et al. 2000).

The similarity in perceptual responses between self-selected and imposed exercise is important to consider when these formats are used for prescriptive purposes. If an individual feels that the level of exertion is lower when self-selected exercise is performed or higher when imposed exercise is performed, the individual may be underestimating or overestimating exertional intensity as it relates to physiological values. However, regardless of these subtle changes in the RPE response, an important aspect of self-selected and imposed exercise to consider is the individual’s adherence to the exercise program. Some individuals may have better adherence during an initial exercise program involving self-selected exercise, yet others may prefer that the exercise professional sets a specific intensity based on established PA guidelines. Therefore, it is important to measure perceptual and psychosocial variables (i.e., RPE, pain, affect, enjoyment) during both self-selected and imposed exercise intensities before determining optimal exercise programming, especially in previously sedentary individuals.