Affect mediates the relationship between physiological and motivational responses to exercise

How the interaction between physiological and motivational responses to exercise contribute to explaining endurance performance is poorly understood. This study investigated whether within-person changes in blood lactate concentration, heart rate (HR), volume of oxygen uptake ($\stackrel{.}{V{O}_2}$) and body temperature underlie desire to reduce effort and performance goal value during incremental exercise. Furthermore, the role of core affect in explaining these relationships was explored. Fifty participants (28 males, 22 females, M_age = 23.52 years; SD = 6.95 years) completed an incremental cycling step test. Work rate increased 25 watts every 4 min until voluntary exhaustion. The three psychological and four physiological measurements were taken at every stage, then analysed using multilevel modelling. Within-person variation in blood lactate concentration predicted desire to reduce effort (b = 2.19, p < .001) and performance goal (b = -0.85, p = .002). $\stackrel{.}{V{O}_2}$ and HR predicted desire to reduce effort (b = 2.64, p < .001; b = 1.59, p = .01), whereas body temperature predicted performance goal (b = 0.58, p = .03). Affect mediated relationships involving blood lactate concentration and $\stackrel{.}{V{O}_2}$, an important mediating variable when applying desire-goal conflicts to exercise. The four physiological responses to exercise have different but significant motivational implications.