Despite awareness of the benefits of engaging in regular physical activity, at least 50% of adults in the US do not meet recommended guidelines for physical activity. One potential explanation for this lack of regular physical activity is that people often experience exercise as affectively unpleasant. Evidence suggests that the more positively people experience exercise (i.e., the better they feel while exercising), the more likely they are to engage in regular physical activity. This may be especially true for people in poor cardiorespiratory condition. In this randomized trial, investigators compared the effects of an affect-guided exercise prescription (intervention) to a heart rate-guided exercise prescription (control) on change in physical activity minutes among previously underactive adults. Investigators also tested whether the effect of the intervention was moderated by differences in cardiorespiratory fitness.

Regular physical activity has many benefits for overall health and well-being, and current public health guidelines recommend at least 150 minutes per week of moderate-to-vigorous intensity activity to attain these benefits. Despite the many benefits of regular activity, the majority of adults in the US fail to meet recommendations for regular physical activity. One potential explanation for suboptimal levels of physical activity is that exercise is often experienced as affectively unpleasant. Recent work has demonstrated that the more positive people feel during exercise, the more likely they are to engage in regular physical activity. Affective response to exercise is modulated by the intensity of the activity: at a vigorous intensity, affective response is almost uniformly negative and unpleasant, whereas at a moderate intensity, there is more inter-individual variability in affective response. Whether the intensity of the exercise is self-selected or imposed also influences the affective response to exercise, with self-selected intensities being experienced as more pleasant. Current recommendations for engaging in physical activity focus on the type of training intensities most likely to result in a negative affective response. The purpose of this pilot trial was to test the effects of an exercise prescription focused on the maintenance of positive affect during exercise. Investigators randomized participants to one of two exercise prescription conditions: (1) an affect-guided prescription focused on maintaining a positive affective response (intervention), and (2) a heart rate-guided prescription focused on maintaining a moderate intensity (control). Investigators tested the effects of these two exercise prescriptions on changes in subsequent physical activity after one week and one month among a sample of underactive adults. Investigators also tested whether the effect of the intervention was moderated by differences in cardiorespiratory fitness.

Inclusion Criteria:

• Physically underactive individuals (< 60 minutes of physical activity/week).

Exclusion Criteria:

• Presence of cardiovascular disease, pulmonary disease, or hypertension.