Changes in ??-Endorphin Levels in Response to Aerobic and Anaerobic Exercise

Abstract

Exercise-induced increases in the peripheral β-endorphin concentration are mainly associated both with changes in pain perception and mood state and are possibly of importance in substrate metabolism. A more precise understanding of opioid function during exercise can be achieved by investigating the changes in β-endorphin concentrations dependent upon intensity and duration of physical exercise and in comparison to other stress hormones. Published studies reveal that incremental graded and short term anaerobic exercise lead to an increase in β-endorphin levels, the extent correlating with the lactate concentration. During incremental graded exercise β-endorphin levels increase when the anaerobic threshold has been exceeded or at the point of an overproportionate increase in lactate. In endurance exercise performed at a steady-state between lactate production and elimination, blood β-endorphin levels do not increase until exercise duration exceeds approximately 1 hour, with the increase being exponential thereafter. β-Endorphin and ACTH are secreted simultaneously during exercise, followed by a delayed release of Cortisol. It is not yet clear whether a relationship exists between the catecholamines and β-endorphin. These results support a possible role of β-endorphin in changes of mood state and pain perception during endurance sports. In predominantly anaerobic exercise the behaviour of β-endorphin depends on the degree of metabolic demand, suggesting an influence of endogenous opioids on anaerobic capacity or acidosis tolerance. Further investigations are necessary to determine the role of β-endorphin in exercise-mediated physiological and psychological events.