Abstract
Objectives: The current study tested the hypothesis that a group-based physical activity (PA) intervention in the worksite would lead to increases in autonomous motivation and perceived competence for PA, self-administered regular PA, and cardiorespiratory fitness, as well as improvements in health (i.e., reduced blood pressure (BP), waist circumference, and improved non-HDL cholesterol levels). Moreover, the study tested the Self-Determination Theory (SDT) process model of health in which the motivational variables would mediate the effect needs support on PA and health. Design: Cluster randomized controlled trial. Method: N = 202 participants from a population of employees working with transport and distribution were cluster randomized (n = 6) to an intervention and a control condition. The group-based worksite intervention was designed based on the tenets of SDT combined with techniques from Motivational Interviewing. Participants were assessed at baseline and at post-test five months later. Results: Complete-case analyses of variance indicated an overall intervention effect, and significant, moderate to small effects sizes (Cohen’s d) in favor of the intervention group on needs support, autonomous motivation and perceived competence for PA, diastolic BP, and cardiorespiratory fitness. The effect sizes were small for all other measures (d’s < .30). Intention-to-treat analyses demonstrated the same pattern with smaller effect sizes. Path analysis obtained a good fit between the data and the SDT process model of health. Conclusions: Offering needs supportive interventions to enhance autonomous motivation and competence for PA among employees resulted in important improvements in cardiorespiratory fitness as well as positive changes in health.
