Findings
Measurement variability arises from different wearable sensor placements, algorithms, and environmental contexts.
Standardized ontologies are needed to ensure consistency in physical activity measurement across digital health studies.
Regulatory agencies, including the FDA, have endorsed specific digital measures such as MVPA as clinical trial endpoints.
Advances in sensor technology and data analysis have improved the feasibility of measuring real-world physical activity with high accuracy.
Additional validation efforts are required for postural sway measures, as current technologies primarily rely on force plates and laboratory-based assessments.

Recommendations
Researchers and developers should adopt standardized ontologies to enhance the comparability of digital measures in clinical research.
Sensor placement and algorithm transparency must be considered to minimize measurement variability in digital endpoints.
Stakeholders should engage with regulatory bodies early to ensure that digital biomarkers meet evidentiary requirements for clinical trials.
Digital health technology developers should prioritize usability and patient-centered design to increase adoption and adherence.
Further research is needed to expand real-world applicability and validation of postural sway measures for clinical and therapeutic use.

Regulatory Considerations
FDA has recognized certain digital measures, such as time spent in MVPA, as valid clinical trial endpoints.
Digital measures used in clinical research should align with HL7 and industry standards for interoperability and data integrity.
Transparency in data processing, including raw data versus processed metrics, is essential for regulatory acceptance.
Developers must ensure compliance with data privacy regulations when collecting real-world physical activity data.
Post-market monitoring of digital endpoints is recommended to ensure continued accuracy and reliability in diverse patient populations.