Before revision:  Given their numerous built-in sensors , smartphones are able to capture detailed and continuous observations on activities of daily living . However, translation of measurements from these consumer-grade devices into research-grade physical activity patterns remains challenging. Over the years, researchers have proposed various human activity recognition (HAR) systems which vary in algorithmic details and statistical principles .
After revision:  Given their numerous built-in sensors , smartphones are able to capture detailed and continuous observations on activities of daily living , making them especially well-suited for health research. Researchers have proposed various human activity recognition (HAR) systems which vary in algorithmic details and statistical principles .