Release of β endorphin and met-enkephalin during exercise in normal women: Response to training

Abstract

Plasma β endorphin and met-enkephalin concentrations were measured in response to treadmill exercises in 15 normal women before, during, and after an intensive programme of exercise training. Significant release of β endorphin occurred in all three test runs, and the pattern and amount of release were not altered by training. Before training dramatic release of met-enkephalin was observed in seven subjects and smaller rises observed in a further four, and this response was almost abolished by training. This represents the first observed 'physiological' stimulus met-enkephalin release. Endogenous opioid peptides play a part in adaptive changes to exercise training and probably contribute to the menstrual disturbances of women athletes.