Date of Award


Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)


Exercise and Health Science

First Advisor

Jessica Whiteley

Second Advisor

Julie Wright

Third Advisor

Sarah Camhi


Introduction: There is little research to date that has been conducted testing theory-based interventions to increase resistance training. We assessed the relative efficacy of Health Action Process Approach (HAPA) based digital intervention for performing resistance training (RT). Methods: The RTinHome study was a three-phase study which recruited adults aged 18-35 not meeting the strength training recommendations. In Phase I, all participants received two Zoom based training sessions over a one-week period. In Phase II, participants were randomized to a no contract control or to a 4-week, HAPA based digital coaching intervention. In Phase III (follow-up) there was no contact with all enrolled participants for four weeks. Attitude and self-efficacy were assessed after the first training session in Phase I. Attitude, self-efficacy, coping planning, behavioral expectations, and intention were assessed at the end of Phase I, at the end of Phase II, and at the end of Phase III. A structural equation model was fit to each data collection point to test treatment effects on behavior. It was hypothesized that the intervention would have positive effects on behavior at the end of Phase II and III. Results: There were significant resistance training behavioral differences between the groups, favoring the intervention group, at the end of Phase II in adherence for both the previous week (last 7 days) (.50 SE=.24; p=0.040) and the previous four weeks (1.92 SE=.90; p=0.033) but not during Phase III. From Phase I to Phase II the intervention had significant effects on self-efficacy (.68 SE =.26), intention (.77 SE=.27), behavioral expectations (19.7 SE=5.3), and coping planning (.43 SE.13). Changes in self-efficacy (2.07 SE=0.83) and intention (3.0 SE=.61) had significant effects on RT behavior at the end of Phase II. In a multiple mediation model, intention mediated the effects of the intervention in Phase II (2.64 SE=.83). Conclusion: The intervention had effects on RT behavior at the end of Phase II but group differences were no longer significant at the end of Phase III.