Prolonged home stay due to quarantine may be associated with side effects that harm people health; one of them is its effect on osteoporosis patients [7].Osteoporosis is a skeletal disease in which there is disturbance of bone mineralization, low bone mass and bone mineral density, decreased bone strength, and increased risk of fractures [8]. With prolonged home stay in quarantine which may lasts for weeks or even months, there is decrease in mechanical loading and exposure to ultraviolet rays which play a major role in disease progression in osteoporotic patients [7]. Mechanical loading improves bone mass and strength, promotes bone formation through stimulation of osteoblasts differentiation, bone mineralization and decrease osteoclasts activity [9]. Additionally, it regulates hormones in the body such as estrogen, testosterone, parathyroid hormone and glucocorticoids which play an important role in bone metabolism and remodeling. Mechanical loading stimulates estrogen production in postmenopausal women which partially mimic hormonal replacement therapy for osteoprosis and Testosterone which reduce bone loss in elderly men [10].Decrease physical activity due to quarantine leads to increase body weight and obesity which has negative effect on skeletal system [11,12]. Insufficient sunlight exposure especially to ultraviolet rays leads to decrease in circulating vitamin D levels (25-hydroxy cholecalciferol) as sunlight exposure mediates the conversion of pre-cholecalciferol (pre vitamin D3) into cholecalciferol (vitamin D3) which then converted into 25(OH)D by liver enzymes. Physical activities that can be done without leaving home help to strengthen muscle using safe, simple, and easy exercises such as walking, dancing, using the stair for climbing or steps exercise cardio training and household working [13]. At least 150 minutes of moderate physical activity or 75 minutes of vigorous physical activity per week or combination of them, avoid long-term sitting down, balanced diet containing calcium, protein and vitamin D [14].Exercise plays a vital role in maintaining a healthy immune system.¹⁵ Walking is considered the best form of exercise which doesn’t require a gym membership or additional equipment. Brisk walking was selected by researchers when they were testing the relationship between exercise and immune function. Brisk walking is defined as walking at a pace of 2.5 to 4.0 miles per hour. It was found that brisk walking for 30-45 minutes per day or, 5 days per week, reduces the respiratory symptoms. The quality of physical exercise a person does influence the immune system. It is affected by the extent and duration reflecting the degree of physiological stress imposed by the workload [15]. Acute bouts of prolonged strenuous exercise cause a temporary depression of various aspects of immune function that last for up to 24h after exercise [16].Although studies are not available for COVID-19, we know that other viruses are much less likely to affect humans who exercise regularly [13]. Intense exercise should be avoided when infected with COVID-19 or other systemic viruses [17]. Sedentary behavior and decreased physical activity can have negative effects well-on the health, being and quality of life of individuals.

For optimal health, it is also important to remember to eat healthily and stay hydrated. Ensure plenty of fruits and vegetables, and limit the intake of salt, sugar and fat. Prefer whole grains rather than refined foods [14]. Psychological stress has a well-known and marked influence on immunity and infection resistance. Athletes may experience psychological stress related to competition, injury, team selection, travel, sleep disruption and jetlag; in addition, .They  are more liable to psychological stress in their personal life related to financial hardship and bereavement. Additionally, athletes experience poor sleep patterns compared with non-athletes.

A disrupted night’s sleep primes the immune system and ameliorates the immune surveillance by stimulating total lymphocytes, cytotoxic T cells and natural killer cells to leave the blood and migrate to potential sites of infection during the early recovery period after exercise when compared with normal sleep pattern [18].

In conclusion, physical exercise induces an immune response according to the duration and intensity of exercise. Thus, moderate physical exercise could have an immunoprotective effect and maintain healthy bones especially in the era of COVID-19 pandemic especially for patients with osteoporosis.