Comparing Cadence vs. Machine Learning based Physical Activity Intensity Classifications: Variations in the Associations of Physical Activity with Mortality

Abstract

BackgroundStep cadence-based and machine-learning (ML) methods have been used to classify physical activity (PA) intensity in health-related research. This study examined the association of intensity-specific PA daily duration with all-cause (ACM) and CVD mortality varied among cadence-based and ML methods in 68,561 UK Biobank participants.MethodsThe two-stage-ML method categorized activity type and then intensity. The one-level-cadence method (1LC) derived intensity duration using all detected steps and cadence thresholds of ≥100 steps/min (moderate intensity) and ≥130 steps/min (vigorous intensity). The two-level-cadence method (2LC) detected ambulatory activities and then steps with the same cadence thresholds.ResultsThe 2LC exhibited the most pronounced association at the lower end of the duration, e.g., the 2LC showed the smallest minimum moderate-to-vigorous PA (MVPA) duration (amount associated with 50% of optimal risk reduction) (2LC vs 1LC vs ML, 2.8 minutes/day [95% CI: 2.6, 2.8] vs 11.1 [10.8, 11.4] vs 14.9 [14.6, 15.2]) while exhibiting similar corresponding ACM hazard ratio (HR) among methods (HR: 0.83 [95% CI: 0.78, 0.88] vs 0.80 [0.76, 0.85] vs 0.82 [0.76, 0.87]). The ML elicited the greatest mortality risk reduction, e.g., for VPA-ACM association, 2LC vs 1LC vs ML: median, 2.0 minutes/day [95% CI: 2.0, 2.0] vs 6.9 [6.9, 7.0] vs 3.2 [3.2, 3.2]; HR, 0.69 [0.61, 0.79] vs 0.68 [0.60, 0.77] vs 0.53 [0.44, 0.64]. After standardizing duration, the ML exhibited the most pronounced associations, e.g., for MPA-CVD mortality, 2LC vs 1LC vs ML, standardized minimum-duration: -0.77 vs - 0.85 vs -0.94; HR 0.82 [0.72, 0.92] vs 0.79 [0.69, 0.90] vs 0.77 [0.69, 0.85].ConclusionThe 2LC exhibited the most pronounced association with mortality at the lower end of the duration. The ML method provided the most pronounced association with mortality after standardizing the durations.