Skeletal Muscle Nonnutritive Blood Flow Increases in Response to a Sit‐to‐Stand Orthostatic Challenge

Physiological challenges that promote skeletal muscle nonnutritive blood flow are not well characterized. We used noninvasive near infrared spectroscopy (NIRS) imaging to test the hypothesis that performing a sit‐to‐stand orthostatic challenge initially increases muscle nonnutritive blood flow. Young healthy participants (n=36, 50% women) underwent three conditions: 1) control: semi‐reclined, lower leg venous occlusion, 2) nutritive control: muscle contraction—five standing calf raises and, 3) challenge: gravity‐induced challenge— sit‐to‐stand. Linear changes in muscle total and deoxygenated hemoglobin resulting from each condition were acquired with NIRS imaging of the lateral calf muscle, and used to calculate the muscle blood flow and oxygen consumption responses, respectively. Muscle blood flow was greater for the sit‐to stand condition than for either the lower leg venous occlusion (p<0.0001), or the nutritive (p=0.01), muscle contraction controls. In contrast, muscle oxygen consumption was greater only for the nutritive control, muscle contraction condition (p<0.0001). NIRS evidence suggests skeletal muscle nonnutritive blood flow is an initial hemodynamic response to an everyday sit‐to‐stand, orthostatic challenge. Skeletal muscle nonnutritive blood flow likely supports improved venous return when assuming an up‐right posture.