Figure 1. Mean oxygen delivery and utilization responses to 13 kg handgrip exercise assessed by conventional measures (left panels) and non-invasive combined NIRS–DCS system (right panels) at heart level.

Blood flow and tissue perfusion responses depicted by Doppler ultrasound-measured forearm blood flow (FBF) indexed to 100 g lean tissue (A) and by DCS-derived muscle blood flow index (BFI) (B). Muscle oxygen utilization responses measured invasively via venous oxygen saturation ($S_{{\text{vO}}_2}$) (C) and non-invasively via NIRS-derived tissue saturation ($S_{{\text{tO}}_2}$) (D). Skeletal muscle oxygen uptake ($\text{m}{\dot{V}}_{{\text{O}}_2}$) (E) and NIRS–DCS-derived muscle relative oxygen uptake (MRO₂) (F) represent the measured oxygen cost of muscular work during handgrip exercise. ***P < 0.001 compared to rest. n = 9. Arrows denote the onset of exercise. Data reported as means ± SEM.