Abstract

Objective: Public health messaging about physical activity (PA) sometimes combines moderate and vigorous intensity, but the variance/invariance of the motives for PA by intensity has received scant attention. Thus, the purpose of this study was to examine the beliefs and motivations associated with regular moderate- and vigorous-intensity PA in a college sample using the framework of Ajzen's Theory of Planned Behavior (TPB). Participants and Methods: A college sample of 337 participants was randomly assigned to complete measures of the TPB framed for either vigorous- or moderate-intensity PA and subsequently completed self-reported measures of PA 2 weeks later. Results: Mean comparisons indicated that participants held higher mean behavioral beliefs about the benefits of vigorous PA for improving appearance and fitness, but vigorous PA was perceived to take more time than moderate-intensity activities. A stacked structural equation model and follow-up Fisher z tests, however, suggested no differences between the associations of TPB constructs with intention or PA by intensity. Conclusions: The findings provide support for the current public health approach of combining moderate and vigorous physical activity messaging through the general invariance of motives by intensity.