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Abstract
This dissertation aimed to quantify the effect of need-supportive instruction on motivational regulations proposed by the Self-Determination Theory (SDT) in physical activity. An additional aim of the dissertation was to examine the efficacy of need-supportive instruction on motivational regulations, skill performance, enjoyment, and state anxiety among college students. Lastly, this dissertation aimed to test whether the effect of need-supportive instruction followed the theoretical model of SDT. The systematic review and meta-analysis of 20 studies showed that need-supportive instruction can increase intrinsic motivation and identified regulation, and decrease amotivation in physical activity. The effects were heterogeneous, with a medium-to-large effect on identified regulation (g = .72; CI 95% [.08, 1.37]) and intrinsic motivation (g = .51; CI 95% [.19, .83]) and a small-to-medium on amotivation (g = -.35; CI 95% [-.66, .05]). The findings support the usefulness of psychological need-supportive instruction in physical activity, but at the same time indicate a demand for high-quality experimental studies examining the effects of need-supportive instruction. The cluster-randomized trial showed that need-supportive instruction improved intrinsic motivation (F(1, 49) = 5.52, p = .023, 2 = .10), skill performance (F(1, 48) = 9.23, p = .004, 2 = .16), and enjoyment (F(1, 49) = 4.89, p = .032, 2 = .09). No effect in state anxiety nor in the other motivational regulations were discovered. The path analysis indicated a positive motivational pathway, with the intervention impacting intrinsic motivation ( = .55), integrated regulation ( = .30) and amotivation ( = -.27), which impacted positively skill performance (R2 = .42) and enjoyment (R2 = .58). The results suggest that need-supportive instruction is beneficial for many important physical activity-related outcomes. Need-supportive instruction seems to affect participants outcomes through both ends of the motivational spectrum.