Supplementary information files for: Motivational processes during physical endurance tasks. Purpose: Motivational processes are insufficiently recognized in models of human endurance. Hence, two studies examined a motivational model proposing that the quality of pre-task autonomous motivation influences performance at high intensity via the in-task temptation to reduce effort and value of goal pursuit. Methods: The studies involved 40 participants each (Study 1: 33% female, Mage = 21.55, SD = 1.97; Study 2: 45% female, Mage = 22.65, SD = 2.61) completing measures of autonomous motivation prior to a ten-minute cycling task. Measures of the temptation to reduce effort and value of goal pursuit were taken every minute during the trial (Study 1) or near the midpoint of the trial (Study 2). Data were analyzed using multilevel growth and parallel mediation models. Results: In both studies, autonomous motivation was associated with lower temptation to reduce effort and higher value of goal pursuit, which were subsequently characteristic of better performance. Study 1 revealed nuances within these relationships depending on whether task initiation or change over time were considered. In Study 2, indirect effects of autonomous motivation on performance via temptation to reduce effort (b = .20, 95% CIs .03 ― .50) and goal value (b = .26, 95% CIs .01 ― .44) were evidenced. Conclusion: Two studies supported a theoretically viable model explaining the dynamics between pre-task and in-task motivation underpinning performance at high intensities.