frailty older adults 10 physical activity 9 aging 8 Medicine 7 machine learning 7 elderly 6 prevalence 6 COVID-19 5 accidental falls 5 clinical 5 mortality 5 quality of life 5 rehabilitation 5 stroke 5 survival 5 telemedicine 5 accelerometer 4 adolescents 4 adults 4 children 4 convolutional neural network 4 deep learning 4 fall risk 4 gait analysis 4 geriatric assessment 4 imaging 4 inflammation 4 postural control 4 reliability 4