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

Abstract Background: Step 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. Methods: The 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. Results: The 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]. Conclusion: The 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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by the National Health and Medical Research Council (NHMRC) through a Leadership level 2 Fellowship to Emmanuel Stamatakis (APP1194510). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Our study utilized data from the UK Biobank, which has received ethical approval from the National Research Ethics Service (Ref 11/NW/0382). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes This research has been conducted using the UK Biobank Resource under Application Number 25813. Bona fide researchers can register and apply to use the UK Biobank dataset at http://ukbiobank.ac.uk/register-apply/.