Exercise intensity is commonly determined using maximal heart rate and maximal oxygen uptake. However, blood lactate levels at different exercise intensities are considered more sensitive biomarkers of endurance performance than maximal oxygen uptake. This study evaluated the validity of exercise intensity determined by blood lactate levels during running and determine the dynamics of blood glucose and β-hydroxybutyrate levels during high- and low-intensity running exercise. Exercise intensities for 12 participants were determined using the lactate curve test. Each participant performed four running tests: low-intensity 30-min, high-intensity 30-min, and low-intensity 60-min running, and no-running (control) tests, with intervals of 1 day to 2 weeks. Blood glucose and β-hydroxybutyrate levels were measured using fingertip puncture blood sampling before and every 30 min (up to 240 min) after the start of running. Blood glucose levels increased significantly immediately after high-intensity 30-min running test compared to the 0-time point. Blood glucose levels decreased to similar levels as that in the 0-min time point 30 min after the 30-min running test. β-hydroxybutyrate levels increased significantly every 30 min after the 150-min time point compared to the levels in the 0-min time point in the high-intensity 30-min and low-intensity 60-min running tests. Using blood lactate measurements obtained from a simple device, we established high-intensity exercise conditions producing transient post-exercise blood glucose increases. Changes in glucose and β-hydroxybutyrate levels reflected energy metabolism shifts across exercise conditions. Further investigation of additional metabolic indicators will help clarify energy metabolism mechanisms at varying exercise intensities.
Kobayashi et al. (Mon,) studied this question.