It is unclear if high-intensity interval training (HIIT) elicits superior improvements in brachial artery (BA) flow-mediated dilation (FMD) responses (i.e., endothelial-dependent vasodilation) than moderate-intensity continuous training (MICT) or resistance training (RT) in otherwise healthy older adults. Whether HIIT enhances lower-limb FMD responses and/or augments low flow-mediated constriction (L-FMC) (endothelial-dependent vasoconstriction) responses more than MICT or RT is also unknown. We tested the hypothesis that HIIT would improve BA and popliteal artery (POP) FMD and L-FMC responses more than MICT or RT in healthy older adults.
Thirty-eight older adults (age, 67 ± 6 yr) performed 6 wk of either HIIT (2 × 20 min bouts alternating between 15-s intervals at 100% of peak power output [PPO] and passive recovery [0% PPO]; n = 12), MICT (34 min at 60% PPO; n = 12), or whole-body RT (8 exercises, 2 × 10 repetitions; n = 14). The L-FMC and FMD were measured before and after training using high-resolution ultrasound and quantified as the percent change in baseline diameter during distal cuff occlusion and after cuff release, respectively.
Resting BA blood flow and vascular conductance (both, P < 0.003) were greater after HIIT only. The HIIT and MICT similarly increased BA-FMD (pre–post: both, P < 0.001), but only HIIT improved BA L-FMC (P < 0.001). Both HIIT and MICT similarly enhanced POP FMD and L-FMC responses (both, P < 0.045). Resistance training did not impact FMD or L-FMC responses in either artery (all, P > 0.20).
HIIT and MICT, but not RT, similarly improved lower-limb vasodilator and vasoconstrictor endothelial function in older adults. Although HIIT and MICT groups enhanced BA vasodilator function, only HIIT improved resting conductance and endothelial sensitivity to low-flow in the BA. In the short-term, HIIT may be most effective at improving peripheral vascular endothelial function in older adults.