Modern advances in communication technology have allowed for the expansion of asynchronous online sport coaching services. In this intra-individual repeated time measures study, the effects of coaching communication scheduling on athletes' affective state and the coach-athlete relationship were observed as well as measures of performance in the squat, bench, and deadlift over a 12 week online coaching period for the sport of powerlifting. Participants (n = 17) with a lifting coefficient DOTS score of (300-399) underwent four days a week of powerlifting training with an online coach. Coaching interactions were randomized between pre-training coaching interactions (PRE), post-training interactions (PST), and no-training interactions (NO) for each training day. Participants took part in multiple daily ecological momentary assessments (EMA) wherein their mood, positive and negative stress, intrinsic motivation, and self-efficacy were measured by mobile app on their smartphones. During the study participants also completed the Coach-athlete Relationship Questionnaire (CART-Q) at pre-study, four weeks, eight weeks, and 12 weeks. A repeated measures ANOVA showed significant improvement from pre-testing to post-testing in all three components of the coach athlete relationship, commitment (Mean difference = 1.729, SD = 0.324, p < 0.001), closeness (Mean Difference = 0.844, SD = 0.230, p= 0.002), and complementarity (Mean Difference = 1.371, SD = 0.254, p < 0.001). Momentary state data were analyzed using multilevel modeling with mixed effects and showed a significant effect of PRE (Est = 0.086, SD = 0.032, t = 2.659, p = 0.012) and PST (Est = 0.084, SD = 0.031, t = 2.702, p = 0.011) coaching interactions on participant valence. The t-test for dependent samples analysis showed participant powerlifting performance significantly improvement from pre to post (Squat ? 7.4, p < 0.001, Bench [delta] 5.5, p < 0.001, Deadlift [delta] 8.6, p < 0.001, Total ? 7.8, p < 0.001, DOTS [delta] 7.7, p < 0.001). Online powerlifting coaching that utilizes frequent communication interactions between coaches and athletes facilitates the growth of the coach-athlete relationship, improves sport performance, and provides opportunities for the coach to have a positive impact on lifter mood prior to and after training. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]