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Returning to physical activity after covid-19

BMJ 2021; 372 doi: (Published 08 January 2021) Cite this as: BMJ 2021;372:m4721

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Better monitoring of physical activity responses post COVID-19 is key

Dear Editor

We commend Salman et al (1) for their guide to a pragmatic risk-stratification for returning to physical activity following COVID-19 infection. The emphasis on both the cardiorespiratory and the psychological screening as well as the prudent and gradual approach “ask, assess and advise/assist”, integrating the subjective feeling of the patients, are highly appreciated. We would like to point out three complementary points that are key for an effective monitoring of COVID-19 patients returning to physical activity.

First, the measurement of pulse oxygen saturation (i.e., pulse oximetry , measurable by low-cost fingertip sensors) was recommended both during admission to the emergency department (2) and at home post-hospitalization (3) as a means to monitor “silent hypoxemia”. Pulse oximetry is especially valuable during and immediately after exercise in COVID-19 patients at least from phase 1 to phase 4 (see figure 1 in (1)).

Second, skeletal muscle function - including mitochondrial fitness (4) - is an important component of health in general (5) and of specific relevance for COVID-19. COVID-19 infection and pandemic-related restrictions of physical activity aggravate the risk of muscle loss and the decrease in strength (6, 7). The monitoring of muscle strength (e.g. using the simple and costless “hang grip” test) is a paramount factor in risk assessment and for consulting of patients returning to physical activity.

Third, the non-invasive assessment of cardiovascular or autonomic responses (i.e., heart rate variability or photoplethysmography via smartwatch (8) or portable wearable (9)) was shown effective for diagnosis of COVID-19 and is a simple means to monitor patient fatigue and coping with post-hospitalization physical activity programmes.

To conclude, we recommend the extension of the authors’ laudable multidisciplinary approach by the additional consideration of oxygen saturation, grip strength and heart rate variability / photoplethysmography for optimal personalized monitoring of COVID-19 patients returning to physical activity.

1. Salman D, Vishnubala D, Le Feuvre P et al. Returning to physical activity after covid-19. BMJ. 2021;372:m4721.
2. Akhavan AR, Habboushe JP, Gulati R et al. Risk Stratification of COVID-19 Patients Using Ambulatory Oxygen Saturation in the Emergency Department. The western journal of emergency medicine. 2020;21(6):5-14.
3. Shenoy N, Luchtel R, Gulani P. Considerations for target oxygen saturation in COVID-19 patients: are we under-shooting? BMC medicine. 2020;18(1):260.
4. Burtscher J, Millet GP, Burtscher M. Low cardiorespiratory and mitochondrial fitness as risk factors in viral infections: implications for COVID-19. Br J Sports Med. 2020.
5. Wolfe RR. The underappreciated role of muscle in health and disease. The American journal of clinical nutrition. 2006;84(3):475-82.
6. Kirwan R, McCullough D, Butler T, Perez de Heredia F, Davies IG, Stewart C. Sarcopenia during COVID-19 lockdown restrictions: long-term health effects of short-term muscle loss. GeroScience. 2020;42(6):1547-78.
7. Wang PY, Li Y, Wang Q. Sarcopenia: An underlying treatment target during the COVID-19 pandemic. Nutrition. 2020;84:111104.
8. Mishra T, Wang M, Metwally AA et al. Pre-symptomatic detection of COVID-19 from smartwatch data. Nat Biomed Eng. 2020;4(12):1208-20.
9. Bourdillon N, Yazdani S, Schmitt L, Millet GP. Effects of COVID-19 lockdown on heart rate variability. PLoS One. 2020;15(11):e0242303.

Competing interests: No competing interests

20 January 2021
Gregoire P Millet
Exercise physiologist / Professor
Nicolas Bourdillon, Johannes Burtscher
University of Lausanne
Institute of Sport Sciences, campus Dorigny, 1015 Lausanne, Switzerland.