Muscle interstitial glucose and lactate levels during dynamic exercise in humans determined by microdialysis

The purpose of the present study was to use the microdialysis technique to determine skeletal muscle interstitial glucose and lactate concentrations d uring dynamic incremental exercise in humans. Microdialysis probes were ins erted into the vastus lateralis muscle, and subjects performed knee extenso r exercise at workloads of 10, 20, 30, 40, and 50 W. The in vivo probe reco veries determined at rest by the internal reference method for glucose and lactate were 28.7 +/- 2.5 and 32.0 +/- 2.7%, respectively. As exercise inte nsity increased, probe recovery also increased, and at the highest workload probe recovery for glucose (61.0 +/- 3.9%) and lactate (66.3 +/- 3.6%) had more than doubled. At rest the interstitial glucose concentration (3.5 +/- 0.2 mM) was lower than both the arterial (5.6 +/- 0.2 mM) and venous (5.3 +/- 0.3 mM) plasma water glucose levels. The interstitial glucose levels re mained lower (P < 0.05) than the arterial and venous plasma water glucose c oncentrations during exercise at all intensities and at 10, 20, 30, and 50 W, respectively. At rest the interstitial lactate concentration (2.5 +/- 0. 2 mM) was higher (P < 0.05) than both the arterial (0.9 +/- 0.2 mM) and ven ous (1.1 +/- 0.2 mM) plasma water lactate levels. This relationship was mai ntained (P < 0.05) during exercise at workloads of 10, 20, and 30 W. These data suggest that interstitial glucose delivery at rest is flow limited and that during exercise changes in the interstitial concentrations of glucose and lactate mirror the changes observed in the venous plasma water compart ments. Furthermore, skeletal muscle contraction results in an increase in t he diffusion coefficient of glucose and lactate within the interstitial spa ce as reflected by an elevation in probe recovery during exercise.