Participants:
This study was a secondary analysis of data collected during the baseline time point of a two-site (Washington University in St. Louis, MO and Shirley Ryan Ability Lab, Chicago, IL) prospective, longitudinal cohort study (NIH R37HD068290). This study recruits individuals without upper limb impairment (e.g., healthy controls) and individuals with upper limb impairment, including people with stroke, multiple sclerosis, distal radius fracture, proximal humerus and/or clavicle fracture, shoulder pain, or breast cancer who were undergoing physical and/or occupational therapy to improve upper limb function. Eligibility criteria for the control cohort included: (1) ≥ 18 years of age, (2) free of neurologic, musculoskeletal, or medical conditions that affect the upper limb or significantly affect physical activity in general. Eligibility for the upper limb impairment cohort included: (1) ≥ 18 years of age, (2) upper limb impairment as judged by a referring physician or surgeon, (3) referral to rehabilitation services to address upper limb impairment, (4) therapist documented goal(s) to increase or restore upper limb function, (5) no other concurrent neurologic, musculoskeletal, or medical conditions that affect the upper limb or physical activity in general, (6) no other co-morbid conditions determined by physician or therapy documentation that indicate a minimal chance for improvement in function (e.g., end-stage cancer diagnosis), (7) not pregnant or planning to become pregnant, (8) no cognitive or communication problems that would prevent them from completing the study. For this analysis, all participants with upper limb impairment were grouped together as we had no scientific reason to suspect that the effects of sleep on the upper limb performance variables would differ based on diagnosis, nor would we have the statistical power to detect these sub-group differences. Only participants who wore the sensors for the full 48-hour wear period were included in this analysis. The study was approved by Washington University’s Institutional Review Board, and all participants signed informed consent prior to engaging in any study procedures. This manuscript was developed in accordance with the STROBE guidelines.
Measures:
All study procedures occurred remotely and study data were collected and managed using REDCap electronic data capture tools housed at Washington University in St. Louis. REDCap (Research Electronic Data Capture) is a secure, web-based software platform designed to support data capture for research studies providing 1) an intuitive interface for validated data capture; 2) audit trails for tracking data manipulation and export procedures; 3) automated export procedures for seamless data downloads to common statistical packages; and 4) procedures for data integration and interoperability with external sources (29, 30). Participants in both cohorts were sent several surveys and two wrist-worn accelerometers to wear for a 48-hour period. The surveys collected demographic information, including age, sex, race, and ethnicity, as well as clinical information (upper limb impairment cohort only). Surveys were completed online or on paper, depending on the participant’s preference, and within one week of wearing the sensors. For the upper limb impairment cohort, participants completed the baseline time point within two weeks of starting outpatient rehabilitation services.
Upper limb accelerometry variables were measured using established, reliable, and valid bilateral wrist-worn accelerometry methodology (31, 32). Participants wore tri-axial GT9X Link accelerometers (ActiGraph Inc, Pensacola, Florida) on each wrist for 48 hours. Participants were instructed to go about their normal routine while wearing the sensors and to keep the sensors on during sleep. Once the sensors were returned to the lab, the data were visually inspected to verify a 48-hour wear period using ActiLife 6 software (ActiGraph Inc, Pensacola, Florida) and exported for further processing.
Upper Limb Performance Variables:
Work is ongoing to determine which sensor-derived variables from upper limb accelerometry are most important for research and clinical practice (33). Thus, we examined 25 variables in total that reflect different aspects of motor behavior of the upper limbs in daily life under the assumption that the relevance of specific variables may vary across research questions, clinical populations, and scientific fields (2, 34-37). Here, we focus on five variables that were previously shown to generate unique clusters of individuals with and without neurologic upper limb deficits (33), and present the remaining 20 variables in the Supplement. Table 1 displays the five upper limb sensor variables and their respective calculations.
Table 1. Description of Upper Limb Sensor Variables*
Variable
|
Description
|
Preferred Time
|
Time (in hours) that the dominant/unaffected limb is moving.
|
Non-Preferred Time
|
Time (in hours) that the non-dominant/affected limb is moving.
|
Use Ratio
|
Ratio of hours of non-dominant/affected limb movement, relative to hours of dominant/unaffected limb movement.
|
Non-Preferred Magnitude
|
Median of the accelerations of the non-dominant/affected limb, in gravitational units (gs)
|
Non-Preferred Magnitude Standard Deviation
|
Standard deviation of the magnitude of accelerations across the non-dominant/affected limb, in gravitational units (gs)
|
*Preferred indicates the dominant limb (control cohort) or unaffected limb (upper limb impairment cohort). Non-preferred indicates the non-dominant limb (control cohort) or affected limb (upper limb impairment cohort).
Data were sampled at 30 Hz, band-pass filtered, and down-sampled into 1-second epochs for each axis by summing the 30 samples within each second. Accelerations in each axis were combined into a single vector magnitude using the formula A vector magnitude threshold of ≥ 2 was used to determine if the upper limb was active for each 1-second epoch (38, 39). To compute the variables preferred time and non-preferred time, each second of activity was summed over the wearing period and converted to hours. The use ratio was calculated as the ratio of non-preferred limb movement relative to the preferred limb movement, expressed in hours. The non-preferred magnitude and standard deviation (Table 1) were converted from activity counts to gravitational units (gs) to present our results in a device-independent manner, facilitating comparisons across the literature.
Sleep Detection:
Actigraphy is a reliable and valid method for detecting sleep, with previous reports demonstrating acceptable to high agreement with polysomnography (40-43). For this study, we employed a multi-step approach to detect sleep using published algorithms (40, 41). Sleep time was determined from the sensor worn on the participant’s preferred upper limb using the methodology described by Schoch and colleagues (41). Briefly, this approach applies the Sadeh sleep algorithm (40) and includes several additional adjustments to improve the algorithm’s accuracy (41). The first adjustment applies a threshold to distinguish between sleep and wake time using the mean vector magnitude for each day of data multiplied by the threshold. Here, we used a threshold of 0.35 because it was best suited to identify sleep in pilot testing. The second adjustment removes periods when the sensors were not worn, which was not applicable for this analysis as all participants wore the sensors for the full 48-hour wear period. The third adjustment utilized criteria by Webster et al (44) to address instances of incorrectly identifying periods of sleep while the participant was awake, via various smoothing routines. The final adjustment involved generating a sleep graph from the previous adjustments and displaying it to the research team member processing the data. The research team member made additional adjustments (if needed) based on any notes made by the participant on their accelerometry wearing log.
For each sensor variable of interest and wearing day, the sensor variable was computed using the full wear time (sleep included) and with sleep time removed (sleep excluded). The effect of sleep was quantified as the difference between sleep included and excluded (i.e., sleep included – sleep excluded). Custom-written R scripts (R Core Team 2021, version 4.2.1) were used for all variable computations and to implement the sleep detection algorithms described above (45, 46).
Statistical Analysis:
Linear mixed effects regression (LMER) was used to address our two study objectives and account for within-participant repeated accelerometry measurement across days (47). For each sensor variable, a LMER model was tested in which the difference between sleep included and excluded was the dependent variable. Each model included a random intercept for participant and fixed effects for day and cohort and their interaction: