Changes in intramuscular blood flow and muscle deoxygenation at different parts of the vastus lateralis during intermittent isometric knee extension in young adult males

Regional differences in oxygen supply-demand balance in active muscles may be related to exercise tolerance. However, the dynamics of oxygen supply-demand balance and its regional differences within active muscles have not been clarified. The purpose of this study was to evaluate regional differences in the patterns of change in the relationship between intramuscular blood flow and muscle deoxygenation along the vastus lateralis length during submaximal isometric knee extension. Thirteen healthy young males (19.4 ± 0.9 years) performed intermittent (5-s contraction and 5-s relaxation) isometric knee extension at 50% of maximal voluntary contraction for 18 contractions. Intramuscular blood flow and deoxy-[hemoglobin+myoglobin] (deoxy-[Hb+Mb]) were simultaneously measured using power Doppler ultrasonography and near-infrared spectroscopy, respectively, at the proximal, middle and distal sites of the vastus lateralis. The ratio of intramuscular blood flow to deoxy-[Hb+Mb] (intramuscular blood flow/deoxy-[Hb+Mb]) was calculated. There was no significant interaction (measurement site × time) for intramuscular blood flow/deoxy-[Hb+Mb] (proximal; 256 ± 138 a.u., middle; 384 ± 228 a.u., distal; 291 ± 197 a.u., F = 1.683, p = 0.076). These results suggest that the balance between oxygen supply and demand is uniformly regulated in the vastus lateralis along its length during intermittent submaximal isometric knee extension.