BACKGROUND: Physical activity guidelines recommend accumulating moderate-to-vigorous physical activity but interpreting and monitoring these recommendations remains challenging. Although step-based metrics from wearable devices offer a simpler approach, their relationship with health outcomes requires validation against established accelerometer measurements.

OBJECTIVES: To evaluate how effectively step-based metrics capture health-related information from accelerometer data and determine optimal step cadence and intensity thresholds associated with cardiometabolic health in middle-aged adults.

METHODS: Cross-sectional data from 4172 participants (aged 50-64 years) in the Swedish CArdioPulmonary bioImage Study (SCAPIS) were analyzed. Physical activity was measured using ActiGraph accelerometers, collecting both step metrics (daily steps and cadence) and full accelerometer data. Both cardiorespiratory fitness, estimated using a submaximal cycle ergometer test, and cardiometabolic health, assessed using a composite score of waist circumference, blood pressure, lipids, and glycated hemoglobin (HbA1c), were considered outcomes. Associations between physical activity and outcomes were examined using linear regression and partial least squares analysis.

RESULTS: Step counting metrics retained 88% of the health-related information from full accelerometer data. The optimal accelerometer intensity associated with cardiometabolic health was around four metabolic equivalents of tasks (METs). A step cadence of 80 steps/min, rather than the commonly used 100 steps/min, appeared more relevant for capturing moderate-intensity activity. Combining step and accelerometer data provided additional explanatory power for cardiometabolic health.

CONCLUSION: Step data capture most of the health-related information from accelerometer-measured physical activity in middle-aged adults. These findings support the use of step-based metrics for assessing and promoting physical activity while suggesting a need for recalibration of intensity thresholds in free-living conditions.