Survivors of critical care illnesses often experience symptoms of post intensive care syndrome (PICS) including declining physical, cognitive, and mental health that arise and persist after hospital discharge (Needham et al., 2012). One of the most common of PICS symptoms is intensive care unit (ICU)-acquired muscle weakness that, if left without treatment, can continue or worsen over time having major negative impacts on quality of life (Hermans and Van den Berghe, 2015). As critical care survivors return to their communities, one important strategy to reduce the residual effects of ICU-acquired weakness and regain their previous quality of life is engaging in physical activity while also reducing sedentary behavior. However, limited information exists regarding critical care survivors’ physical activity and sedentary behavior levels after being discharged to their homes (Gandotra et al., 2021). Although authors have reported that hospitalized adults in general have increased their physical activity and reduced sedentary behavior post-hospital discharge (Kirk et al., 2021), the opposite situation has been reported for ICU survivors; ICU survivors have demonstrated reduced physical activity levels at hospital discharge (Herridge et al., 2003), as well as up to 5 years post-discharge (Herridge et al., 2011). Furthermore, the reduction in post-discharge physical activity has been associated with increased mortality, and inability to resume previous activities that were part of the survivor’s quality of life, particularly among middle-aged and older adults (Brown et al., 2012, Samitz et al., 2011). In a study of 107 ICU survivors who were employed prior to their ICU admission, after 6 months 22 (21 %) could not return to their previous job, 25 (23 %) had reduced their working hours, and 31 (29 %) had not returned to work at all due to their health. Survivors who could not return to work were middle age (33–60 years old; m = 46.8) and reported, among other symptoms, difficulty with concentration, mobility, standing for long periods, and walking long distances (Hodgson et al., 2018).

Physical activity measures vary widely in their use and psychometric properties (Dowd et al., 2018). Tools measuring physical activity and to a lesser extent sedentary behavior, range from self-report via diary or survey, to indirect measures via caloric expenditure such as the gold-standard measure of doubly-labelled water, and using wearable activity tracker devices (e.g., accelerometers, pedometers, activity monitors, wearable tracking devices, and hereinafter referred to as “wearable activity trackers”) that can assess variables such as steps per day or activity counts in various intensities of activity. Given the high cost and limited access of doubly-labelled water, and the potential biases resulting from self-report methods (Dowd et al., 2018), assessing physical activity and sedentary behavior using wearable activity trackers provides some advantages for the measurement of these behaviors. Further, ICU survivors may be frail necessitating slower activities, yet little is known about the utility and outcomes of using wearable activity trackers in this population; the closest comparisons are among older adults in general (Chan et al., 2017).

The few existing studies of critical care survivors that involved wearable activity trackers have used different measurement devices resulting in varied results making it difficult to compare outcomes across studies (Gluck et al., 2017). Thus, to date, data collected using wearable activity trackers has not been summarized to specifically capture comparable baseline levels of physical activity and sedentary behavior upon discharge to home. Understanding baseline levels of active and sedentary behaviors upon returning home is important for the design of interventions to improve the health of critical care survivors as they re-enter their communities and return to their previous employment. Therefore, the aims of the current study were to describe the levels of physical activity and sedentary behavior measured via wearable activity trackers in middle-aged ICU survivors who have been discharged home and to identify research gaps in this field. Middle-aged adults, aged 45–64 (Warren, 2019), were specifically targeted for this review because this understudied population (Lachman, 2015) falls within the average age of ICU survivors (Garland et al., 2013, Righy et al., 2019). Additionally, middle-aged adults are typically employed, engaged in family and community activities, and generally contribute to society. If compromised, middle-aged ICU survivors are at risk of becoming dependent on society and societal resources.