Differences in vascular function between trained and untrained limbs assessed by near-infrared spectroscopy

Purpose: The aim of this study was to examine whether differences in vascular responsiveness associated with training status would be more prominent in the trained limb (leg) than in the untrained limb (arm) microvasculature. Methods: Thirteen untrained (26 ± 5 year) and twelve trained (29 ± 4 year) healthy men were submitted to a vascular occlusion test (VOT) (2 min baseline, 5 min occlusion, and 8 min re-oxygenation). The oxygen saturation signal (StO₂) was assessed using near-infrared spectroscopy (NIRS) throughout the VOT. Vascular responsiveness within the microvasculature was evaluated by the re-oxygenation Slope 2 (Slope 2 StO₂) and the area under the curve (StO_2AUC) of (StO₂) signal during re-oxygenation in the leg and arm. Results: There was a significant interaction between training status and limb for the slope 2 StO₂ (P < 0.01). The leg of the trained group showed a steeper slope 2 StO₂ (1.35 ± 0.12% s⁻¹) when compared to the slope 2 StO₂ of the leg in their untrained counterparts (0.86 ± 0.09% s⁻¹) (P < 0.05). There was a medium effect size of 0.58 for slope 2 StO₂ on the arm and a large effect size of 1.21 for slope 2 StO₂ on the leg. In addition, there was a small effect size of 0.24 for StO_2AUC on the arm and a medium effect size of 0.64 for StO_2AUC on the leg. Conclusion: The present study suggests that the vascular adaptations induced by lower limb endurance exercise training are more prominent in the trained limb than in the untrained limb microvasculature.