Influence of running speed and exercise duration on blood glucose threshold during long-distance running

Abstract

This study was intended to clarify 1) the difference of the exercise intensity at blood lactate threshold (LT) and blood glucose threshold (GT), 2) the effect of exercise duration on the LT and GT during two sets of incremental running test. Ten male runners (age 25.0±3.2 yr, height 171.2 ±5.5 cm, body mass 57.9±4.0 kg, VO2max 64.6±3.0 ml/kg/min) completed two sets of incremental running test (each set was set to run ten stages at 60-90% VO2max) Second set was repeated after 8 min recovery. LT and GT speed were investigated at the first set. Lactate minimum (LM) and glucose minimum (GM) speed were selected where the blood lactate and glucose concentration were at the lowest during the second set. Using the indirect calorimetry (VO2, VCO2), fat and carbohydrate oxidation rates were calculated. GT was observed in all runners. VO2 and energy expenditure were similar between the two incremental running tests, however, fat oxidation was significantly higher and carbohydrate oxidation was significantly lower during the first half of the second set. This change was regarded as the influence of the exercise duration in the first set. Furthermore, GM speed was significantly lower than GT speed, but LM speed and LT speed were not different. It was considered that the shift of GT was affected by the substrate utilization change during prolonged exercise.