  With the rapid development of the internet of things (IoT) and artificial
intelligence (AI) technologies, human activity recognition (HAR) has been
applied in a variety of domains such as security and surveillance, human-robot
interaction, and entertainment. Even though a number of surveys and review
papers have been published, there is a lack of HAR overview papers focusing on
healthcare applications that use wearable sensors. Therefore, we fill in the
gap by presenting this overview paper. In particular, we present our projects
to illustrate the system design of HAR applications for healthcare. Our
projects include early mobility identification of human activities for
intensive care unit (ICU) patients and gait analysis of Duchenne muscular
dystrophy (DMD) patients. We cover essential components of designing HAR
systems including sensor factors (e.g., type, number, and placement location),
AI model selection (e.g., classical machine learning models versus deep
learning models), and feature engineering. In addition, we highlight the
challenges of such healthcare-oriented HAR systems and propose several research
opportunities for both the medical and the computer science community.

Human-Computer Interaction;Machine Learning;Signal Processing