Biphasic changes in 3-methylhistidine excretion in humans after exercise.

We previously reported that 3-methylhistidine excretion was increased in human subjects after a strenuous bout of exercise. Because other investigators have not corroborated this finding, we undertook the present study to investigate the conditions that result in decreased and increased 3-methylhistidine excretion in human subjects after exercise. Four experiments were performed: a cross-sectional study comparing 3-methylhistidine excretion in endurance-trained subjects with untrained controls, a longitudinal study of 3-methylhistidine excretion by female basketball players before the start of the season and again during the competitive season, an experiment to determine changes in 3-methylhistidine excretion as a result of 2 h of exercise each day for 7 consecutive days, and a study to determine changes in 3-methylhistidine excretion during 4-h intervals after a strenuous exercise bout. The 3-methylhistidine-to-creatinine ratio was approximately 20% higher for trained than nontrained subjects. In three separate experiments a biphasic change of 3-methylhistidine excretion was observed in response to exercise with an immediate decrease in the 3-methylhistidine-to-creatinine ratio during exercise followed by a prolonged increase. The magnitudes of the negative and positive responses determine whether one observes an increase, no change, or a decrease in the total daily excretion of 3-methylhistidine.