Abstract
The use of exercise intervention in hypoxia has grown in popularity amongst patients, with encouraging results compared to similar intervention in normoxia. The prescription of exercise for patients largely rely on heart rate recordings (percentage of maximal heart rate (HRmax) or heart rate reserve). It is known that HRmax decreases with high altitude and the duration of the stay (acclimatization). At an altitude typically chosen for training (2,000-3,500 m) conflicting results have been found. Whether or not this decrease exists or not is of importance since the results of previous studies assessing hypoxic training based on HR may be biased due to improper intensity. By pooling the results of 86 studies, this literature review emphasizes that HRmax decreases progressively with increasing hypoxia. The dose–response is roughly linear and starts at a low altitude, but with large inter-study variabilities. Sex or age does not seem to be a major contributor in the HRmax decline with altitude. Rather, it seems that the greater the reduction in arterial oxygen saturation, the greater the reduction in HRmax, due to an over activity of the parasympathetic nervous system. Only a few studies reported HRmax at sea/low level and altitude with patients. Altogether, due to very different experimental design, it is difficult to draw firm conclusions in these different clinical categories of people. Hence, forthcoming studies in specific groups of patients are required to properly evaluate (1) the HRmax change during acute hypoxia and the contributing factors, and (2) the physiological and clinical effects of exercise training in hypoxia with adequate prescription of exercise training intensity if based on heart rate.
Highlights
Hypoxia is defined as a reduction in the amount of oxygen (O2) available to any cell, tissue, or organism (Semenza, 2009)
In the current literature search, we found 322 groups for whom both SaO2 and HRmax at the end of an incremental exercise to exhaustion in normoxia and hypoxia were reported
A body of scientific literature exists on the evaluation of passive exposure and/or exercise training in altitude/hypoxic environment in healthy subjects
Summary
Hypoxia is defined as a reduction in the amount of oxygen (O2) available to any cell, tissue, or organism (Semenza, 2009). Intermittent exposure to hypoxia at rest is considered as an alternative nonpharmacological therapy (Serebrovskaya and Xi, 2016; Leone and Lalande, 2017), even though a thorough evaluation of its effectiveness has yet to be performed (Wilson et al, 2018) Based on these observations, several authors have suggested that exercise intervention in a hypoxic environment should be used with patients (Chapman et al, 1999; Millet et al, 2016b; Hobbins et al, 2017). This literature review presents an examination of the available literature on HRmax decrement with increasing hypoxia in both healthy subjects and patients, with the main aim of providing a general understanding of the use of HRmax as a benchmark for exercise training prescription in hypoxia
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