Limb Specific Vascular Adjustments at Exercise Onset

Abstract

ObjectiveTo compare the rate of vascular adjustment at the onset of arm vs. leg exercise using the same exercise modality and hydrostatic conditions.Methods10 healthy recreationally active males (21.9±1.9 yrs) completed step increase dynamic exercise protocols (1s contract/2s relax) at 40%, 80% and 100% of peak vascular conductance response. Forearm handgrip and knee extension was performed in supine position with the exercising muscles at heart level. Continuous measures of brachial (forearm) and femoral (leg) artery blood flow (FBF, LBF; Doppler and Echo ultrasound) and arterial blood pressure (MAP; Finometer) were used to calculate forearm (FVC) and leg (LVC) vascular conductance.ResultsFor all exercise intensities, LVC was (p<0.001) but FVC was not (P=0.705) characterized by a subsequent vasoconstriction at ~10 s (Phase IB) following the rapid initial vasodilation (Phase IA). Phase IA LVC amplitude was greater than steady state in the leg at 40% and no different at 80% (P<0.05), but for FVC it was lower than steady state at all exercise intensities (P<0.05). Phase IA had a greater contribution to the total response amplitude in the leg vs. forearm at all exercise intensities (P<0.05) representing an overshoot compared to the Phase II plateau at 40% and 80% (P<0.05). There was a main effect of limb for the Phase II time constant (leg faster than forearm, P<0.05).ConclusionWhen contraction/relaxation modality and hydrostatic environment are controlled for, rapid vasodilatory mechanisms are more sensitive to the onset of exercise in lower vs. upper limbs and can overshoot steady state. Transient vasoconstriction between the initial rapid and secondary slower adjustment is specific to the lower limb. Funding: NSERC 250367‐06.