<p>Employees in contemporary work environments frequently face negative health impacts from sedentary behavior, such as musculoskeletal pain in the neck, shoulders, or lower body. This study reanalyzes data from a 3-month longitudinal randomized controlled intervention trial involving office-workers from five organizations alongside previously unpublished data from the same trial. The trial demonstrated that office-yoga and walking interventions effectively reduced musculoskeletal complaints (MSC) compared to a waitlist control group. This research aims to uncover the role of temporal dynamics of MSC that enhance and explain the success of these interventions. Drawing on self-regulation and psychological momentum theory, we hypothesize that employees who experience initial successes in terms of initial velocity and acceleration of MSC reduction show an increased intervention adherence which predicts intervention effectiveness. Based on social cognitive theory and the theory of planned behavior, we investigate how participants’ pre-intervention attitude toward the intervention and their outcome expectations predict initial adherence and subsequent temporal dynamics of health changes in a serial mediation model. Results from Bayesian Latent Acceleration Modelling revealed that initial velocity and acceleration of MSC reduction predicted intervention effectiveness. However, adherence did not mediate this relationship. Furthermore, a gradually increasing amount of walking was found beneficial. Attitude toward the intervention predicted initial adherence only in the walking group, while findings regarding outcome expectations were non-significant. This research emphasizes the importance of temporal dynamics, especially the initial temporal dynamics of health changes, for the effectiveness of workplace physical activity interventions and offers new directions for occupational health research and practice.</p>