1. Introduction

One of the world's leading causes of preventable death is the lack of physical activity (PA) per se [1-5]. Recent researches show the effects of exercise against non-communicable diseases (NCDs: cardiovascular diseases, cancers, chronic respiratory diseases and diabetes) as an adjuvant therapeutic agent [6,7], positively related to decreased mortality and increased quality of life, and negatively linked to the incidence or effect of diseases [8,9]. The continuation of daily exercise and PA in a secure home setting should therefore be a priority during the COVID-19 period for a healthy life. However, the COVID-19 pandemic created an unparalleled condition that had an unprecedented effect on most of humanity, in almost all domains of life [PA was no exception, [10-12]]. Due to the imminent rise in loneliness (self-isolation) and physical inactivity, organizations with a global scope instantly hurried to stress the importance of PA for society and to highlight pre-existing exercise guidelines for a more physically active life in order to prevent any impending adverse effects.

Unfortunately, the well-documented advantages of PA, i.e. defense against the virus and against the development of NCDs [3], seem to have been mostly underestimated or generally neglected by the community and the current drastic policies, which have favored a substantial degree of inactivity (Figure 1), [10-12]. More specifically, a series of very recent studies have demonstrated the deleterious impact of the COVID-19 restrictive orders to stay at home and avoid wider socialization on PA [13–17] and a clear association on overall negative change in PA (Figure 2), [10-12]. In any case, during and after lockdown the dominance of physical inactivity has posed many great challenges to health and sport officials, medical professionals and practitioners, professional and recreational athletes and the community. For these reasons, we would like to highlight the benefit of physically active life and daily exercise training (not intense or exhaustive) for public health, especially for the most vulnerable groups (people with serious underlying health conditions or elderly) [3,18,19].

Figure 1: Physical activities by daily occupation, transportation to and from daily occupation, leisure time activities, and regular sporting activities, on a weekly basis in Greek adults (n=8495), [12]. The 95%CI of change in overall PA (from the Pre lockdown to Lockdown conditions) was –17.3 to –15.4. Abbreviations: CI, confidence interval; PA, physical activity.

Figure 2: Overall PA (daily occupation, transportation to and from daily occupation, leisure time activities, and regular sporting activities) pre and during COVID-19 lockdown conditions in Greek adults [12]. Data are presented as mean ± SE. * p < 0.05, significant difference in all groups between conditions. † p< 0.05, significant interaction effect of lockdown on the PA subgroups (Males and High PA). Abbreviations: MET, metabolic equivalent task (=3.5 mLO₂/kg/min); PA, physical activity.

2. The Positive Effects of Physical Activity

In order to minimize the risk of COVID-19 spread in the population, physical distancing and self-isolation steps have been used in most countries worldwide. leading to intensified behavioral routines that contribute to physical inactivity [10-12], potentially anxiety, depression and the growth of other NCDs [3,18,19]. Contrariwise, PA and routine daily exercise training are strategically necessary to maintain an acceptable health status and reverse the sedentary lifestyle [3].

A physically active lifestyle, outdoor sports activities and exercise may be a powerful combination to resolve the negative effects of the COVID-19 crisis on public health, particularly for the most vulnerable groups [19]. Physical activity amplifies the quality of life and has been negatively related to the incidence or effects of diseases and mortality. More precisely, in various diseases, PA strengthens the immune system and function, either in chronic systemic inflammation or after vaccination [20-22]. A regular exercise of mild to moderate intensity releases millions of immune cells (T cells, macrophages) and proteins (cytokines), which in turn allow the immune system to function better in inflammatory and stressful environments [20,23]. Physical activity is effective in both the prevention and treatment of NCDs, all of which increase the risk of morbidity and mortality among COVID-19 infected people [3,19]. Lack of PA and decreased daily energy expenditure, on the other hand, can contribute to a substantial increase in body fat, further loss and decrease in mitochondrial function, increased chronic oxidative stress and inflammation, deteriorating muscle, blood vessel and bone conditions and also degrade the already depleted cardiorespiratory reserves and immunity function of vulnerable groups [19,24,25]. In addition, inactivity per se is one of the world's main causes of preventable death [26].

As the pandemic COVID-19 outbreak continues, symptoms of psychological stress increase [18], causing imbalances between cortisol and other hormones, which adversely affect the biological response to inflammation and the immune system itself [27]. A PA lifestyle, on the contrary, has major mental health benefits: it decreases symptoms of depression and anxiety to COVID-19 pandemic stress and restores cortisol equilibrium [28]. Furthermore, frequent PA and daily exercise in individuals aged 65 years have beneficial effects on aging and related conditions, increase cognitive function and self-esteem, decrease the risk of falling, help prevent sarcopenia and dynapenia, and ultimately help prevent frailty [23].

As numerous new cases of COVID-19 appear daily in the world, many healthy individuals are being asked by official authorities to remain in self-quarantine at home. Being active during the COVID-19 pandemic crisis, while all national public health directives and general hygiene rules must be respected, is a challenge for everyone. Nevertheless, the World Health Organization has detailed recommendations on the manner and the amount of PA individuals should carry out to achieve favorable cardiovascular and metabolic health effects [24,29]. Briefly, infants (~1 year old) must be physically involved in activities several times a day [30]. Children ~3-4 years must be moderately to vigorously active for at least an hour a day and children aged ~5 years should be physically active for at least 180 minutes a day [30]. Children and adolescents (~5-17 years of age) should have at least 60 minutes of moderate-to-vigorous-intensity physical activity a day, including muscle and bone building exercises, at least 3 days a week [24]. Adults aged ≥ 18 years should have a total of at least 150 minutes of PA of moderate intensity during the week or at least 75 minutes of PA of vigorous intensity during the week, including 2 or more days a week of muscle-strengthening activities [24]. In order to improve balance and avoid falls, older adults (≥ 60 years) with poor mobility should have PA 3 or more days a week [24]. In the current COVID-19 pandemic situation, adults people in self-quarantine without any signs or diagnosis of acute respiratory disease, 150 min of moderate-intensity PA, or 75 min of vigorous-intensity PA, or a combination of both is recommended per week [29,31]. It is worth emphasizing that these guidelines can be followed at home, without special facilities and in a limited space. However, it is of paramount importance to keep in mind that any PA is always better than none.

3. Conclusion

Despite the fact that intensive efforts have been made worldwide to find a pharmaceutical agent and vaccine to battle COVID-19, the value of PA and non-exhaustive exercise as countermeasures and adjuvant therapeutic agents against the virus, NCDs and mental health disorders arising from the COVID-19 crisis should not be underestimated. Therefore, daily PA and exercise during the COVID-19 pandemic in a safe environment for a healthy life is absolutely necessary.

Authors’ Contributions

All authors contributed to writing this manuscript. All authors have read and approved the final version of this manuscript and agree with the order of presentation of the authors.

Declaration of Conflicting Interests

The authors declare no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

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