Understanding the factors that will lead individuals to increase and maintain their levels of physical activity is a key area of investigation within exercise psychology. Research has suggested that the affective responses that individuals experience during exercise may have a role in predicting future exercise behaviour (Kiviniemi, Voss-Humke & Seifert, 2007; Williams, Dunsiger, Ciccolo, Lewis, Albrecht & Marcus, 2008). Thus, it is important to ensure individuals experience positive exercise-induced affective responses. Both exercise intensity and the method of exercise prescription are factors that have been shown to influence exercise-induced affective responses. For example, self-selected intensities have been shown to result in more positive and less variable affective responses than exercise imposed at the same intensity (e.g., Rose & Parfitt, 2007). However, the extent to which a self-selected versus imposed intensity method of prescription influences exercise motivation and behaviour has not been examined in a longitudinal investigation. The purpose of the current research was to compare the affective responses to exercise, levels of self-determined motivation and physical activity behaviour that results from a six-week intervention of self-selected versus imposed intensity exercise.
A single-subject multiple baseline case design was used to identify individual differences in exercise preference and affective responses and gain in-depth information on the cognitive appraisal process and behavioural outcomes without losing external validity. Six females aged 39-49 years participated in a six week intervention consisting of 30 min of aerobic exercise three times a week. Three participants exercised at a self-selected intensity and three at an imposed intensity based on the relative intensity they self-selected at baseline. Affect, self-determined motivation, self-efficacy and physical activity behaviour were measured weekly throughout the intervention and six weeks post-intervention.
The results showed that, as expected, the intensities chosen between participants were variable. Participants in the imposed condition selected intensities that were below their Ventilatory Threshold (VT) at baseline. Participants in the self-selected group selected a mixture of intensities (one below, one at, and one above VT). As expected, two of the three participants in the imposed condition had less positive affective responses during the intervention, while in the self-selected condition affect remained positive throughout the intervention despite higher intensities being selected. Participants in both conditions increased their physical activity behaviour to the same extent from baseline to follow up. Perceived control decreased in two of the imposed intensity participants, showing the successful manipulation of choice. Two participants in each condition had increased intrinsic and introjected regulation as well as perceived volition and a more internal locus of causality across the six week intervention. The study has highlighted the impact that loss of control over exercise intensity can have on affective responses even when the intensity is imposed at a previously self-selected level. This loss of control did not appear to impact physical activity behaviour as participants in both conditions increased from their baseline levels. Exercise professionals must recognise that individuals differ in their preferred exercise intensity and through allowing individuals to self-select their exercise intensity can provide the autonomy support necessary to result in positive affective responses.
