Lactate release in relation to tissue lactate in human skeletal muscle during exercise

In four healthy volunteers, muscle lactate concentration and the release of lactate from the leg were determined at rest and at 4 and 12 min of sitting bicycle exercise at four intensities (30, 50, 70, and 90% of maximal oxygen uptake). The muscle biopsies were obtained by needle biopsy technique from m. vastus lateralis. The rate of lactate release was calculated from the femoral venous-arterial differences of lactate and the leg blood flow was determined by constant rate dye infusion. Both leg blood flow and leg oxygen consumption increased linearly with work intensity. The release of lactate rose approximately linearly with the muscle lactate concentration up to about 4-5 mmol/min but then the relationship revealed a clear leveling off. These results indicate a maximal level for the lactate release from the exercising muscles with a translocation hindrance for lactate within the muscles.