Muscle reoxygenation difference between superficial and deep regions of the muscles during static knee extension

The purpose of this study was to test the hypothesis that differences in vertical spatial difference in reoxygenation after exercise exists, reflecting heterogeneity of muscle oxygenation during exercise might be due to the difference in dominantly recruited muscle fiber type.

Ten healthy female subjects performed 1 min static knee extension exercise at low (30%) and high (60%) fraction of maximal voluntary contraction (MVC). Muscle oxygenation in the vastus lateralis (VL) was monitored using multi channel near-infrared spectroscopy. Half time reoxygenation (T(1/2)reoxy) after exercise was calculated from oxygenated hemoglobin in the eight channels which changed the distance between light source and detector distances at 2,3,4,5 cm. Blood flow (BF) in the femoral artery was measured by Doppler ultrasound. Mean arterial blood pressure (BP) at the end of the exercise was assessed by a Finometer device.

BF during exercise did not differ significantly during exercise at low and high intensity, whereas BP was elevated at high intensity. T(1/2)reoxy tended to be prolonged at high intensity. It would be due to a transition of muscle fiber recruitment from type I toward type II fiber dominance, and/or insufficient oxygen supply for increased demand in the muscle. T(1/2)reoxy in different light source and detector distances was not different among them.

This study demonstrated that the reoxygenation in the superficial region did not differ from that in the deeper region, including superficial, even when exercise intensity was high.