It is established that isometric handgrip (IHG) training reduces resting arterial blood pressure (ABP) in hypertensives and normotensives. However, the mechanisms are unclear. The aim of this project was to test whether IHG training with one arm improves endothelium-dependent vasodilation (EDD) including that mediated by nitric oxide (NO) and prostacyclin (PGI2) in young White European (WE) men, and in young South Asian (SA) and older WE men who have recognised endothelial dysfunction.
IHG training was performed with the dominant hand, (four 3-minute contractions at 30% of their maximum voluntary contraction (MVC) at 5 min intervals) 4 days/week for 4 weeks. MVC was increased in the trained arm, but not the non-trained arm of all groups; resting ABP was reduced in older men only. However, IHG training increased muscle performance in the non-trained and trained arm of all groups during rhythmic handgrip at 60% MVC for 3 min. Further, exercise hyperaemia evoked by these contractions, and reactive hyperaemia were increased in both the trained arm and non-trained arm of young and older WE, but not in the non-trained arm of young SA men. In addition, IHG training augmented the increased venous efflux of NO metabolites from the non-trained arm during reactive hyperaemia in older men, but decreased it in young WE and SA men, whilst augmenting the increase in PGI2 efflux in young SA men only. Finally, during a single bout of IHG training, limb blood flow increased progressively with repeated IHGs in contralateral arm and ipsilateral leg of WEs, and to a lesser extend in forearm of SAs. These responses were attenuated by cyclooxygenase (COX) inhibition in WEs but enhanced in SAs implicating vasodilator and vasoconstrictor COX products respectively.
These new findings indicate that just 4 weeks of IHG training improves muscle performance and endothelial dilator function in young healthy WE men and particularly in older WE men, but not in young SAs. The acute effects of IHG training on blood flow in the resting limbs are consistent with shear stress providing the stimulus for improved endothelium-dependent dilatation in young and older WEs but suggest the release of vasoconstrictor COX products may limit the beneficial effects in young SAs. The mechanisms require further investigation. However, in older WE men, IHG training may provide a useful, non-pharmacological tool for improving EDD and reducing ABP and cardiovascular risk, but more intense or longer IHG training may be required even in young SA men to achieve such effects.
Keywords: Isometric handgrip training, hypertension, arterial blood pressure, endothelium dependent vasodilation, South Asian ethnicity, ageing
