1. Introduction
n 31 December 2019, a viral pneumonia that started in Wuhan, China, was reported to the World Health Organization (WHO). The new Coronavirus Disease (COVID-19) spread rapidly worldwide such that until 11 September 2020, it infected more than 28,328,131 people in 215 countries and killed 388,047 people [1]. In order to prevent the spread of COVID-19, in almost all areas, various protection measures have been taken by the authorities, including the closure of schools and universities, restrictions on travel and holding of cultural and sports events, and the closure of private and public sports clubs [2]. Implementing an physical activity program to perform at home during the lock down and COVID-19 epidemic, which may last for weeks to months, can reduce the negative physiological and psychological effects of sedentary behavior patterns. This article review programs and recommendations for physical activity at home in people with sedentary lifestyles according to the guidelines of the American College of Sports Medicine (ACSM).
Rating of Perceived Exertion Scale
Rating of Perceived Exertion (RPE) scale can be used to adjust the intensity during aerobic and endurance exercises. Various factors such as age, gender, previous training status and fitness level [12] as well as external environmental factors such as ambient temperature [13] may affect RPE. Other environmental factors such as listening to music, watching TV, altitude, nutritional considerations and external feedback can also influence RPE. However, studies suggested that despite the potential impact of these factors, RPE is still a valid monitoring tool [13].
Heart rate, a variable for controlling the exercise intensity
Heart rate is the most common way to control the intensity of aerobic exercise. This is due to the close relationship between heart rate and oxygen consumption, especially when its intensity is between 50 and 90% of functional capacity (VO2max). Heart Rate Reserve (HRR) is the difference between a person’s maximum Heart Rate (HRmax) (estimating as age - 220) and resting Heart Rate (HRrest) [14]. The most accurate way to regulate the intensity of aerobic exercise using this method is to determine a specific heart rate with a VO2max or heart rate associated with lactate threshold. To estimate and identify intensities with the highest accuracy, laboratory conditions and specialized tools are required. If these facilities are not available, predicting maximal heart rate using age factor (age-220) can be used as a basis for determining exercise intensity.
Body weight resistance exercise program
The combination of resistance exercise has been highly recommended due to its positive effects on maintaining or increasing the skeletal muscle mass, strength, and fitness. The current guidelines of the ACSM state that resistance exercise should be performed at an intensity of less than 60% of one-repetition maximum (<60% 1RM) to improve neuromuscular function [17]. Recent studies in US have shown that resistance exercise has many health benefits for people and can deal with problems such as muscle loss due to aging, physical disabilities, chronic illness and even premature death [18]. Numerous studies have shown that resistance exercise improves cognitive function, concentration, insulin sensitivity and blood lipid profile; reduces anxiety and blood sugar; increases basal metabolic rate; controls body weight, and many other physiological benefits [19]. Table 1 presents the body weight resistance exercise program at home for different target groups [1].


2. Conclusion
Due to concerns about the growing prevalence of COVID-19, precautions need to be taken. Staying at home is an essential safety step that can lower the prevalence rate. Many countries now have implemented restrictions that make people stay home and only go out in an emergency. Staying home for long periods of time, however, can increase behaviors that lead to inactivity, anxiety, and depression, which in turn can lead to a sedentary lifestyle and cause a wide range of psychological problems [20]. The best way to solve these problems is to replace outdoor activities with home activities such as body weight resistance exercise and aerobic exercise (if possible by using treadmills and stationary bikes) based on standard protocols, in addition to having a healthy diet during this period. Maintaining regular physical activity and daily exercise in a safe home environment is an important strategy for a healthy lifestyle during a COVID-19 pandemic. Home activities provide an opportunity for people to stay healthy by performing simple movements. One of the limitations of the present study was the difficulty reviewing all available papers; hence, we tried to review reliable and up-to-date papers in the field of sports science.

Ethical Considerations
Compliance with ethical guidelines
This article is a review article with no human or animal sample.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
The authors observed the criteria of the International Committee of Medical Journal Editors (ICMJE). Conceptualization: Mohammad Parastesh; Methodology and data collection: Jalil Moradi; Writing, editing & review: All authors.

Conflicts of interest
The authors declare no conflict of interest.


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