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Received Nov 24, 2017; Revised Mar 30, 2018; Accepted Apr 4, 2018
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1. Introduction
Reduced physical activity in older adults is associated with increased risk of disease and mortality [1, 2], and it is well established that exercise training reduces the risk of disease and disability [3]. High-intensity interval training (HIIT) has been proposed as an effective and time efficient method for increasing aerobic capacity and metabolic health in young and older adults [3–8]. HIIT sessions are typically short (15–300 s), intense (70–100% of maximum) bursts of activity interspaced with 1–5 min of rest [9]. This training differs from traditional endurance training that involves prolonged and continuous exercise supplied mainly by aerobic energy system [10, 11].
There is little agreement on the extent to which the benefits of HIIT can be attributed to the exercise intensity alone among the other load variables [12, 13]. Training at both moderate to high (70–80%) and near-maximal (>90%) intensity can significantly improve health parameters [13]. Place et al. [7] have shown that repetitive maximal intensity (all-out) 30 s cycling bouts induce a long-lasting increase in resting intracellular sarcoplasmic calcium concentration ([Ca2+]i), which triggers the mechanism responsible for adaptations. These findings favor “higher-the-better” strategy when considering exercise intensity. All-out efforts of HIIT currently prevails in increasing endurance of various age and physical condition groups [4, 14, 15].
Despite the well-documented HIIT benefits, it is important to consider that very intense exercise can cause significant build-up of metabolites that can induce unpleasant sensations [6]. Practical observations during the laboratory experiments showed that as little as one 30 s all-out cycling bout may induce dizziness or collapse, even in well-trained athletes. These side effects could diminish motivation and preclude systematic and long-term implementation of all-out HIIT in general population. Moreover, because of side effects issues, it is doubtful whether prescription of maximal intensity HIIT to some specific populations such as older people is safe and effective. At the same time, moderate to high-intensity training has been shown to provide beneficial effects even for patients with a chronic disease [16].
These challenges have encouraged further...