Ankle position modifies tibialis anterior muscle perfusion and oxygenation in the human leg

Abstract

Near‐infrared spectroscopy (NIRS) is a noninvasive technique used to monitor muscle oxygenation. Photoplethysmography (PPG) is a noninvasive measure of muscle microvascular blood flow. NIRS and PPG were used in seven tibialis anterior (TA) muscles of five healthy volunteers (3 male, 2 female) aged 31.2±7.8 years (mean, SD) in order to determine whether oxygenation and blood flow of the TA varied with ankle position. Data from the resting ankle position (mean of 11.5º plantarflexion) were compared to following test positions: full passive plantarflexion (PF), passive neutral (Neu) or 0º, and full passive dorsiflexion (DF). Mean oxygenation of the TA muscle yielded significant decreases for PF (p<0.01) and DF (p<0.01), but no significant difference for Neu (p=0.10). Mean perfusion of the TA muscle increased significantly for PF (p=0.027), Neu (p=0.012), and DF (p=0.010). Based on prior research, it was expected that oxygenation levels would decrease across the test ankle positions; however, it was not anticipated that perfusion would increase. Our novel results suggest that local compensatory vasodilation within muscle exists in order to increase microvascular blood flow under conditions of relative tissue hypoxia. These findings are important to the understanding of the local hemodynamic response in the human leg in relation to changes in ankle position from rest.