title: Shear stress mediates endothelial adaptations to exercise training in humans.
abstract: Although episodic changes in shear stress have been proposed as the mechanism responsible for the effects of exercise training on the vasculature, this hypothesis has not been directly addressed in humans. We examined brachial artery flow-mediated dilation, an index of NO-mediated endothelial function, in healthy men in response to an acute bout of handgrip exercise and across an 8-week period of bilateral handgrip training. Shear stress responses were attenuated in one arm by cuff inflation to 60 mm Hg. Similar increases were observed in grip strength and forearm volume and girth in both limbs. Acute bouts of handgrip exercise increased shear rate (P<0.005) and flow-mediated dilation percentage (P<0.05) in the uncuffed limb, whereas no changes were evident in the cuffed arm. Handgrip training increased flow-mediated dilation percentage in the noncuffed limb at weeks 2, 4, and 6 (P<0.001), whereas no changes were observed in the cuffed arm. Brachial artery peak reactive hyperemia, an index of resistance artery remodeling, progressively increased with training in the noncuffed limb (P<0.001 and 0.004); no changes were evident in the cuffed arm. Neither acute nor chronic shear manipulation during exercise influenced endothelium-independent glyceryl trinitrate responses. These results demonstrate that exercise-induced changes in shear provide the principal physiological stimulus to adaptation in flow-mediated endothelial function and vascular remodeling in response to exercise training in healthy humans.
authors.affiliation: Research Institute for Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom.
authors.forename: Toni M
authors.initials: TM
authors.lastname: Tinken
authors.forename: Dick H J
authors.initials: DH
authors.lastname: Thijssen
authors.forename: Nicola
authors.initials: N
authors.lastname: Hopkins
authors.forename: Ellen A
authors.initials: EA
authors.lastname: Dawson
authors.forename: N Timothy
authors.initials: NT
authors.lastname: Cable
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Green
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000704:Analysis of Variance; D000886:Anthropometry; D001783:Blood Flow Velocity; D001916:Brachial Artery / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology*; D005080:Exercise Test / Q000379:methods; D005542:Forearm / Q000098:blood supply*; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D011336:Probability; D012016:Reference Values; D012494:Sampling Studies; D033081:Shear Strength; D013997:Time Factors; D014655:Vascular Resistance / Q000502:physiology; D055815:Young Adult