RESUMEN
PURPOSE: The desire-goal motivational conflict helps explain endurance performance; however, the physiological concomitants are unknown. The present study examined disturbances in desire to reduce effort and performance goal value across moderate, heavy, and severe exercise intensity domains, demarcated by the first (LT1) and second (LT2) lactate thresholds. In addition, the within-person relationships among blood lactate concentration, heart rate, and desire-goal conflict were examined. METHODS: Thirty participants (53% female, Mage = 21.03 years; SD = 2.06 years) completed an incremental cycling exercise test, in which work rate was increased by 25 watts every four minutes, until voluntary exhaustion or sufficient data from the severe intensity domain had been collected. Desire to reduce effort, performance goal value, blood lactate concentration (for determination of LT1 and LT2), and heart rate were measured at the end of each stage and analyzed using multilevel models. RESULTS: The desire to reduce effort increased over the exercise test with additional shifts and accelerations after each lactate threshold. The performance goal did not show general declines, nor did it shift at LT1. However, the performance goal value shifted at LT2, and the rate of change increased at both thresholds. Within-person variation in blood lactate concentration positively correlated with the desire to reduce effort and negatively correlated with the performance goal. Within-person variation in heart rate correlated with desire to reduce effort but not the performance goal. CONCLUSION: Transitioning through both lactate thresholds is important phases for motivation during progressive exercise, particularly for the desire to reduce effort. Within-person variation in blood lactate concentration is more influential for motivation, compared with heart rate.