## 2 Physical Activity during the COVID-19 Pandemic
The cardiovascular and pre-frailty risk assessment score using age, daily steps, resting heart rate, and sleep duration was developed in this study; four out of five subjects increased the score during the self-isolation period, and two out of five subjects were considered to have an increased cardiovascular and pre-frailty risk due to self-isolation. This study suggests that self-isolation is harmful for physical health and increases the risk of cardiovascular disease and frailty. The authors undoubtedly expect that smartwatches or other medical wearables will play an essential role in telemedicine when a public health emergency, such as a pandemic, occurs. [PERSON] et al. [23] investigated the impact of social isolation during the COVID-19 pandemic on wellbeing in older adults. There were a total of 10 adults who were aged \(\geq\)75 years or \(\geq\)65 years with a risk of falling. Physical activity and sleep were monitored using a wearable pendant device (ActivePERS/PAMSys). Study subjects wore the wearable pendant device for two consecutive days, and posture (sitting%, standing%, lying%, and walking%), walking characteristics (daily step count, number of walking bouts, and cadence), postural transition, activity behavior (prolonged sitting and light- and moderate- to vigorous-intensity activities), and sleep quality (time in bed) were measured. The daily step count (from 5911 \(\pm\) 1193 to 2655 \(\pm\) 419 steps), number of walking bouts (from 241.3 \(\pm\) 56.2 to 148.6 \(\pm\) 27.1), number of postural transitions (from 720.7 \(\pm\) 162.2 to 399.4 \(\pm\) 68.5), standing% (from 16.5 \(\pm\) 2.3% to 11.1 \(\pm\) 1.8%), and walking% (from 6.7 \(\pm\) 1.3 to 3.2 \(\pm\) 0.5%) were significantly decreased, and sitting% (from 37.5 \(\pm\) 4.5% to 45.2 \(\pm\) 5.1%) was significantly increased during the COVID-19 pandemic compared with those before the pandemic. Furthermore, depression symptoms evaluated by the Center for Epidemiologic Studies Depression scale significantly increased from 3.0 \(\pm\) 0.7 to 7.5 \(\pm\) 2.4 during the pandemic. However, sleep quality did not change. Depression symptoms were also correlated with deterioration in daily physical activity such as a decline in cadence and increase in time in bed and prolonged sitting time. Social isolation during the pandemic has a negative impact on daily physical activity and mental health in older adults. [PERSON] et al. [24] investigated how physical activity, sedentary behavior, and stress changed during the first month of the COVID-19 pandemic. Subjects who regularly used wearable activity trackers were recruited via social media, and 121 participants completed the study. Physical activity was objectively measured by wearable activity trackers manufactured by Apple, Fitbit, Samsung, and Garmin. The daily step count was decreased from 9509 \(\pm\) 3390 to 8497 \(\pm\) 3620 steps, whereas the sedentary time was increased from 181.79 \(\pm\) 117.9 to 299.6 \(\pm\) 136.6 min per day from pre- to post-COVID-19. However, 55 participants reported that their physical activity was increased; on the other hand, an equal number of participants reported that their physical activity was decreased, and 11 participants reported that their physical activity did not change. There seems to be a discrepancy between objectively measured physical activity and self-reported physical activity during the pandemic. Major reasons/barriers to changes in physical activity were access/equipment and motivation in participants whose self-reported physical activity was decreased and time in participants whose self-reported physical activity was increased during the pandemic. Daily and work stresses were significantly increased due to COVID-19, and a decrease in physical activity was associated with a larger work stress.