Feasibility of Activity Monitors to Assess Physical Capacity After Critical Illness: An Observational Study Nested Within a Randomized Clinical Trial

Objective To determine if daily physical performance measures collected remotely via a wrist-worn activity monitor (AM) could serve as a reliable alternative to the clinic-based 6-minute walk test (6MWT) for assessing physical capacity after critical illness. Patients and Methods Participants were recruited from a group of critically ill adults >18 years of age with moderate-to-severe anemia as they enrolled in a parallel group, single-center randomized clinical trial assessing the impact of a multifaceted anemia prevention and treatment strategy versus standard care at intensive care units (ICUs) at a large US medical center. The nested prospective observational study was conducted from September 2022 through October 2025. Participants were instructed to wear a wrist-worn AM for four days in their free-living environments at 1- and 3-months post-hospitalization to coincide with their clinic-based 6MWTs. Mean daily step counts and maximum daily cadences were calculated from the AM. Results Fifty-two participants (median [interquartile range] age, 66 [60-71]; 29 men) were enrolled. Over 80% of participants completed monitoring and provided valid data. Mean daily step count (r s =0.557 , P=0.001) and mean maximum daily cadence (r s =0.830, P<0.001) were positively correlated with 6MWT distance. There were no significant differences between the trial's intervention groups. Conclusion Home-based wrist-worn AM use is feasible after critical illness with high retention and compliance rates. The strong correlation between daily maximum cadence and 6MWT distance suggests this device can effectively evaluate physical performance and recovery in ICU survivors remotely. These findings provide valuable preliminary data to guide the design of large clinical trials.