Six weeks of high-intensity interval training enhances contractile activity induced vascular reactivity and skeletal muscle perfusion in older adults

Philip J J Herrod,Kenneth Smith,Bethan E Phillips,Philip J Atherton,John P Williams,Jonathan N Lund

doi:10.1007/s11357-021-00463-6

Abstract

Impairments in muscle microvascular function are associated with the pathogenesis of sarcopenia and cardiovascular disease. High-intensity interval training (HIIT) is an intervention by which a myriad of beneficial skeletal muscle/cardiovascular adaptations have been reported across age, including capillarisation and improved endothelial function. Herein, we hypothesised that HIIT would enhance muscle microvascular blood flow and vascular reactivity to acute contractile activity in older adults, reflecting HIIT-induced vascular remodelling. In a randomised controlled-trial, twenty-five healthy older adults aged 65–85 years (mean BMI 27.0) were randomised to 6-week HIIT or a no-intervention control period of an equal duration. Measures of microvascular responses to a single bout of muscle contractions (i.e. knee extensions) were made in the m. vastus lateralis using contrast-enhanced ultrasound during a continuous intravenous infusion of Sonovue™ contrast agent, before and after the intervention period, with concomitant assessments of cardiorespiratory fitness and resting blood pressure. HIIT led to improvements in anaerobic threshold (13.2 ± 3.4 vs. 15.3 ± 3.8 ml/kg/min, P < 0.001), dynamic exercise capacity (145 ± 60 vs. 159 ± 59 W, P < 0.001) and resting (systolic) blood pressure (142 ± 15 vs. 133 ± 11 mmHg, P < 0.01). Notably, HIIT elicited significant increases in microvascular blood flow responses to acute contractile activity (1.8 ± 0.63 vs. 2.3 ± 0.8 (arbitrary contrast units (AU), P < 0.01)), with no change in any of these parameters observed in the control group. Six weeks HIIT improves skeletal muscle microvascular responsiveness to acute contractile activity in the form of active hyperaemia-induced by a single bout of resistance exercise. These findings likely reflect reports of enhanced large vessel distensibility, improved endothelial function, and muscle capillarisation following HIIT. Moreover, our findings illustrate that HIIT may be effective in mitigating deleterious alterations in muscle microvascular mediated aspects of sarcopenia.

Highlights

In terms of the clinical relevance of these deficits in vascular function, it is possible that out with vascular disease per se, they may contribute to the pathogenesis of insulin resistance [32] via impaired delivery of insulin [10, 37], and may be implicated in the development of hypertension [14]
In one participant assigned to the High-intensity interval training (HIIT) group, measurement of microvascular blood flow (MBF) was not achieved due to cannula failure leading to contrast extravasation
One participant allocated to the control group did not return for the post intervention visit and was lost to follow-up

Summary

Introduction

High-intensity interval training (HIIT) is an alternative training mode to traditional moderate intensity continuous training (MICT) which may potentially engender increased uptake and adherence due to its time-efficiency (i.e., shorter session duration [33]) and ability to quickly improve factors pertaining to cardiorespiratory health and fitness in both young [4] and older [25] adults. Supporting this notion, a systematic review and meta-analysis of 65 studies concluded that HIIT has the ability to improve cardiorespiratory fitness over both short- (< 12–weeks) and longer-term training durations [2]. Not all studies have demonstrated superiority of HIIT when compared to MICT [19, 21], in terms of absolute improvements in cardiorespiratory fitness, its time-efficient nature is unquestionable [24]

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Conclusion