The Association Between Real Life-Assessed Sit-to-Stand and Stand-to-Sit Kinematics with Self-Reported Levels of Physical and Mental Fatigue in Neurodegenerative and Immune-Mediated Inflammatory Diseases

Fatigue is a complex, multi-faceted phenomenon that is particularly common in immune-mediated inflammatory disease and neurodegenerative disease cohorts. Clinical assessment of fatigue relies heavily on patient-reported outcomes (PROs), that provide only the perception aspect of fatigue and poorly capture fluctuations over time. The use of wearable sensors, e.g., inertial measurement units, overcome these drawbacks, by allowing for the assessment of capacity and performance aspects of health through continuous monitoring of daily life activities. However, the relation between daily life activities that are prerequisite for functional independence, such as sit-to-stand and stand-to-sit transitions, and fatigue, is not well established, thus this study aims to quantify the association between kinematic features of sit-to-stand and stand-to-sit transitions and self-reported physical and mental fatigue. Study participants wore an IMU on the lower back for four consecutive weeks, and continued their daily life activities as usual, thereby reporting their physical and mental fatigue four times per day on a 7-point Likert scale via a smartphone application. Sit-to-stand and stand-to-sit transitions were detected using a validated algorithm, and kinematic features were derived from those transitions. The association between the kinematic features and PROs were researched using mixed effects models, with fatigue modelled as the independent variable and the median, 95th and 5th percentiles of the kinematic features from a 2-hour aggregation window centred around the time of administration of a PRO. The results suggested 5th and 95th percentiles of selected kinematic features were associated with fatigue across different disease cohorts. Furthermore, it was hypothesised that with more fatigue standing up is performed with more effort that is needed, whereas with more physical fatigue sitting down is performed with less control of the body movement, i.e., people drop down on their chair or sofa. In conclusion, this study showed the potential of selected kinematic features of sit-to-stand and stand-to-sit movements as intermediate clinical endpoints to reflect aspects of fatigue.