Acute High-Intensity Interval Exercise in Multiple Sclerosis with Mobility Disability

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Dear Editor-in-Chief, High-intensity interval training (HIIT) to improve a variety of physiologic outcomes is growing in popularity among clinical populations. However, limited evidence exists for HIIT among individuals with multiple sclerosis with high mobility disability (1–3). Thus, we read the article by Hubbard et al. (4) with great excitement. This study concluded that HIIT was feasible, safe, and elicited several positive responses, including increased power output, oxygen consumption, and heart rate response, as compared with continuous steady-state aerobic exercise (CON). However, we have apprehension regarding the authors’ suggestion that extending the duration of CON to match HIIT exercise volume (i.e., work) would decrease ecologic validity. Conversely, we argue that to generalize study findings to real-world settings (e.g., clinic based and community based), the comparison of exercise intensity must be done while matching exercise volume. When providing exercise intensity recommendations in real-world settings, the other exercise prescription variables (i.e., frequency, time, and type) must be considered. For example, the exercise guidelines for healthy adults recommend twice the amount of time for moderate (150 min·wk−1) versus vigorous (75 min·wk−1) of aerobic exercise (5,6). Thus, although there may be an increased time burden for CON to achieve the same exercise volume or total workload as HIIT, the time versus intensity trade-off is necessary when providing exercise recommendations or designing exercise programs. In the study by Hubbard et al. (4), both HIIT and CON completed exercise bouts of the same duration, resulting in a greater exercise volume during HIIT sessions (i.e., total work was 1.4 times higher during the HIIT vs CON session). To increase ecological validity, we suggest that the duration of CON sessions should have been increased. We illustrate how these sessions could have been matched for exercise volume using the following metabolic equation: Based on this equation, the HIIT session in Hubbard et al. (4) resulted in the following: Thus, to match the 62 MET·min achieved in the HIIT sessions, the CON sessions needed to increase their duration from 20 to 28 min. We commend the authors for exploring the utility of HIIT among individuals with MS with high mobility disability, as this population is often understudied in the context of exercise interventions. However, we suggest that future studies examining similar exercise protocols should consider increasing the duration of CON sessions to match exercise volume achieved during HIIT sessions. We believe this will enhance ecological validity by mimicking the time versus intensity dance that is common in the practice of exercise recommendation and prescription in clinic and community-based settings. Mary C. Hidde Matthew Howell Alexa DeBord Department of Health and Exercise Science Colorado State University Fort Collins CO Heather J. Leach Department of Health and Exercise Science Colorado State University Fort Collins CO; and Colorado School of Public Health Aurora, CO

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