Evidence of a limb and shear stress stimulus profile dependent impact of high intensity cycling training on flow-mediated dilation.

Abstract

Lower limb endurance training can improve conduit artery flow-mediated dilation (FMD) in response to transient increases in shear stress (reactive hyperemia; RH-FMD) in both the upper and lower limbs. Sustained increases in shear stress recruit a partially distinct transduction pathway and elicit a physiologically relevant FMD response (SS-FMD) that provides distinct information regarding endothelial function. However, the impact of training on SS-FMD is not well understood. The purpose of this study was to determine the impact of cycling training on handgrip exercise induced brachial artery(BA) FMD (BA SS-FMD) and calf plantar-flexion induced superficial femoral artery (SFA) FMD (SFA SS-FMD). RH-FMD was also assessed in both arteries. 28 young males were randomized to control (n=12) or training (n=16) groups. The training group cycled 30 min/day, 3 days/week for 4 weeks at 80% heart rate reserve. FMD was assessed in the BA and SFA pre- and post-intervention via Duplex ultrasound. Results are mean ±SD. Training did not impact SS-FMD in either artery, and SFA RH-FMD was also unchanged (p>0.05). When controlling for the shear rate stimulus via covariate analysis, BA RH-FMD improved in the training group (p=0.05)(Control: pre- 5.7±2.4%, post- 5.3±2.4%; Training: pre- 5.4±2.5%, post- 7.2±2.4%). Thus, endurance training resulted in non-uniform adaptations to endothelial function, with an isolated impact on the BA s ability to transduce a transient increase in shear stress. • Training did not alter SS-FMD in the arm or leg. • RH-FMD was augmented in the arm only. • Thus training adaptations were limb and shear stress profile specific.