Systemic adaptations to exercise training in skin microcirculation in humans

Introduction: Exercise training of the lower limbs mediates localised conduit and resistance artery adaptations in the active region and systemic adaptations in the upper limbs. These changes to the vasculature are largelymediated through elevations in shear stress. Whether microcirculatory vascular responses to lower limb training occur systemically, and whether shear stress contributes to such adaptations, is currently unknown. Methods: Nine subjects completed an 8-week cycle ergometer training study, with unilateral cuff inflation around the forearm to unilaterally manipulate upper limb blood flow and shear stress during each exercise bout. To test skin microvascular function at 0, 4 and 8 weeks of exercise training, we measured laser-Doppler skin flux in response to localised disk heating at 33, 42 and 44 ◦C. Cutaneous vascular conductance was derived from skin flux and blood pressure values. Results: Acutely, the onset of cycling increased skin flux (12.1±4.1 to 131.7±35.0 PU) and temperature (31.7±0.4 to 33.6±0.9 ◦C), whilst in the cuffed arm (60mmHg) skin flux (11.91±2.22 to 52.92PU) and temperature (31.5±0.3 to 31.7±0.8 ◦C) responses were attenuated or absent (2-way ANOVA interaction-effect; both P<0.001). Chronically, after 8 weeks of cycling, skin flux responses during the plateau phase of heating at 42 ◦C (3.19±0.32 to 2.38±0.41PU/mmHg) and 44 ◦C (3.65±0.30 to 2.84±0.44PU/mmHg) were significantly lower in the uncuffed arm, but unchanged in the cuffed limb at (42 ◦C: 3.10±0.36 to 2.76±0.30PU/mmHg, 44 ◦C: 3.70±0.39 to 3.46±0.30PU/mmHg). Discussion: Cycling exercise is associated with increased skin perfusion in the upper limbs, an effect which is ameliorated by placement of a pressure cuff. Cycle training decreased the skin vasodilator response to an identical local heating stimulus, suggesting enlargement of the capillary bed and associated increase in skin blood flow transit time. We speculate that this impact of leg exercise training in the upper limbs may enhance systemic heat loss following training. No changes in the contra-lateral cuffed arm were apparent, suggesting that repeated increases in shear stress may mediate some of this adaptation in the skin microcirculation as a result exercise training.