Noninvasive and in vivo assessment of upper and lower limb skeletal muscle oxidative metabolism activity and microvascular responses to glucose ingestion in humans

This study investigated changes in muscle oxidative metabolism and microvascular responsiveness induced by glucose ingestion in the upper and lower limbs using near-infrared spectroscopy (NIRS). Fourteen individuals (aged 27 ± 1.4 years) underwent 5 vascular occlusion tests (VOT) (pre-intervention (Pre), 30 min, 60 min, 90 min, and 120 min after glucose challenge). NIRS-derived oxygen saturation (StO₂) was measured on the forearm and leg muscle at each VOT. Muscle oxidative metabolism was determined by the StO₂ downslope during cuff inflation (deoxygenation slope); microvascular responsiveness was estimated by the StO₂ upslope (reperfusion slope) following cuff deflation. There was a significant increase in arm (p < 0.05; 1-β = 0.860) and leg (p < 0.05; 1-β = 1.000) oxidative metabolism activity as represented by the faster deoxygenation slope at 60, 90, and 120 min (0.08 ± 0.03, 0.08 ± 0.03, 0.08 ± 0.02%·s^–1, respectively) (leg) and at 90 min (0.16 ± 0.08%·s⁻¹) (arm) observed after glucose ingestion when compared with their respective Pre values (leg = 0.06 ± 0.02; arm = 0.11 ± 0.04%·s⁻¹). There was a significant increase in arm (p < 0.05; 1-β = 0.880) and leg (p < 0.05; 1-β = 0.983) reperfusion slope at 60 min (arm = 3.63 ± 2.1%·s⁻¹; leg = 1.56 ± 0.6%·s⁻¹), 90 min (arm = 3.91 ± 2.1%·s⁻¹; leg = 1.60 ± 0.6%·s⁻¹), and 120 min (arm = 3.91 ± 1.6%·s⁻¹; leg = 1.54 ± 0.6%·s⁻¹) when compared with their Pre values (arm = 2.79 ± 1.7%·s⁻¹; leg = 1.26 ± 0.5%·s⁻¹). Our findings showed that NIRS–VOT technique is capable of detecting postprandial changes in muscle oxidative metabolism activity and microvascular reactivity in the upper and lower limb. Novelty • NIRS-VOT is a promising noninvasive clinical approach that may help in the early, limb-specific detection of impairments in glucose oxidation and microvascular function.