Lactate production without hypoxia in skeletal muscle during electrical cycling: Crossover study of femoral venous-arterial differences in healthy volunteers
Abstract
BACKGROUND: Aim of the study was to compare metabolic response of leg skeletal muscle during functional electrical stimulation-driven unloaded cycling (FES) to that seen during volitional supine cycling. METHODS: Fourteen healthy volunteers were exposed in random order to supine cycling, either volitional (10-25-50 W, 10 min) or FES assisted (unloaded, 10 min) in a crossover design.
Whole body and leg muscle metabolism were assessed by indirect calorimetry with concomitant repeated measurements of femoral venous-arterial differences of blood gases, glucose, lactate and amino acids. RESULTS: Unloaded FES cycling, but not volitional exercise, led to a significant increase in across-leg lactate production (from -1.1+-2.1 to 5.5+-7.4 mmol/min, p<0.001) and mild elevation of arterial lactate (from 1.8+-0.7 to 2.5+-0.8 mM).
This occurred without widening of across-leg veno-arterial (VA) O2 and CO2 gaps. Femoral SvO2 difference was directly proportional to VA difference of lactate (R2 = 0.60, p = 0.002).
Across-leg glucose uptake did not change with either type of exercise. Systemic oxygen consumption increased with FES cycling to similarly to 25W volitional exercise (138+-29% resp. 124+-23% of baseline).
There was a net uptake of branched-chain amino acids and net release of Alanine from skeletal muscle, which were unaltered by either type of exercise. CONCLUSIONS: Unloaded FES cycling, but not volitional exercise causes significant lactate production without hypoxia in skeletal muscle.
This phenomenon can be significant in vulnerable patients' groups.