Plasma substrate response in men and women during marathon running

Venous blood samples from three male and four female subjects were taken in conjunction with a 26.2-mi marathon race prior to the start (control), at 17 mi, and immediately after the finish. Plasma concentrations of glucose and free fatty acids (FFA) were determined, and the ratio of unsaturated to saturated FFA (U/S FFA) was calculated. Compared to the control value, glucose was unchanged at the finish despite a slight increase at 17 mi (not significant). FFA increased significantly (p less than 0.05) from control to finish and from 17 mi to finish in both groups. The U/S FFA ratio also increased progressively from control to finish. No significant differences were found between male and female groups for any of the measured values. We conclude that blood glucose is maintained at normal levels during prolonged heavy exercise in trained women as in men, and that FFA availability increases with time during strenuous exercise in both sexes.