Purpose The aim of this study was to systematically review the literature on accelerometer-measured physical activity and health outcomes in adults. Methods Eight electronic databases were searched for relevant articles published up to March 2021. Only population-based studies of adults (age ≥18 yr) that directly compared two or more categories of physical activity (i.e., bout duration, intensity, and daily/weekly frequency) with a health outcome (e.g., mortality, cardiometabolic, healthy aging, depression, sleep, and brain structure) were included. Results Of the 15,923 publications retrieved, 52 articles were included. Twenty-eight studies directly compared the associations between physical activity accumulated in different bout durations, 31 studies directly compared the associations between physical activity accumulated in different intensities, and 9 studies directly compared the associations between the effects of varying daily and weekly frequencies of physical activity, with health outcomes. Most showed no differences in relationships with health outcomes when physical activity was accumulated in short (<10-min) or long (≥10-min) bouts. Overall, there were no differences in the relationships with most health outcomes when different intensities and daily/weekly frequencies were compared. However, in most studies, researchers did not adjust their analyses for total volume of physical activity. Moreover, variations in researcher-driven decisions about data collection and processing methods made it difficult to compare study findings. Conclusions These findings suggest that physical activity accumulated in many patterns of bout duration, intensity, or daily/weekly frequency is associated with a range of beneficial health outcomes in adults. Lack of adjustment for total volume of physical activity in most studies and inconsistent methods for defining components of physical activity prevent firm conclusions about which specific patterns of bout duration, intensity, and daily/weekly frequency are most important for health benefits.