To the Editor: We read with great interest the paper by Carr et al. in the September 3 issue1 on the relation between exercise and β-endorphin secretion in women. We have previously reported a study in which five untrained subjects (four men and one woman) 26 to 35 years old ran for 20 minutes on a treadmill at a speed that was adjusted to maintain the heart rate at 80 per cent of maximum.2 Plasma samples were obtained before and after exercise, and β-endorphin immunoreactivity was measured by radioimmunoassay. There was a 440 per cent mean increase in circulating β-endorphin.
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