Reliability of Wearable-Sensor-Derived Measures of Physical Activity in Wheelchair-Dependent Spinal Cord Injured Patients

Abstract

Physical activity (PA) has been shown to have a positive influence on functional recovery in patients after a spinal cord injury (SCI). Hence, it can act as a confounder in clinical intervention studies. Wearable sensors are used to quantify PA in various neurological conditions. However, there is a lack of knowledge about the inter-day reliability of PA measures. The objective of this study was to investigate the single-day reliability of various PA measures in patients with a SCI and to propose recommendations on how many days of PA measurements are required to obtain reliable results. For this, PA of 63 wheelchair-dependent patients with a SCI were measured using wearable sensors. Patients of all age ranges (49.3 ± 16.6 years) and levels of injury (from C1 to L2, ASIA A-D) were included for this study and assessed at three to four different time periods during inpatient rehabilitation (2 weeks, 1 month, 3 months, and if applicable 6 months after injury) and after in-patient rehabilitation in their home-environment (at least 6 months after injury). The metrics of interest were total activity counts, PA intensity levels, metrics of wheeling quantity and metrics of movement quality. Activity counts showed consistently high single-day reliabilities, while measures of PA intensity levels considerably varied depending on the rehabilitation progress. Single-day reliabilities of metrics of movement quantity decreased with rehabilitation progress, while metrics of movement quality increased. To achieve a mean reliability of 0.8, we found that three continuous recording days are required for out-patients, and 2 days for in-patients. Furthermore, the results show similar weekday and weekend wheeling activity for in- and out-patients. To our knowledge, this is the first study to investigate the reliability of an extended set of sensor-based measures of PA in both acute and chronic wheelchair-dependent SCI patients. The results provide recommendations for sensor-based assessments of PA in clinical SCI studies.

Keywords: intervention studies; physical activity; rehabilitation; reliability; spinal cord injury; wearable sensors.

Figure 1

Photograph of one examiner wearing the sensors. One sensor was attached to the right wheel of each wheelchair, one sensor was attached to each wrist.

Figure 2

Measurement protocol. This study consists of two observational studies. In the 1st observational study, patients were measured at 5 time points during the rehabilitation process. In the 2nd observational study, a different patient cohort was measured only once, at least 1 year after injury. In stages VA, A I, A II, and partly A III of the 1st observational study, patients were in-patients (red). In the 2nd observational study, as well as partly in A III, and stage C of the 1st observational study, patients were out-patients (blue). At each time point (^*), acceleration and angular velocity of the right and left wrists were recorded for 3 days, while the acceleration of the right wheel of the wheelchair was recorded for 7 days. Overall upper limb activity (AC) and PA based on energy expenditure (SED, LPA, and MVPA) were calculated based on the 3 day recordings. All wheeling-related measures (DIST_TOT, DIST_ACT, and VEL) were calculated based on the 7 day recordings.

Figure 3

ICC values representing the single-day reliabilities for (A) activity counts (AC); (B) time spent in sedentary activity (SED), low physical activity (LPA), and moderate-to-vigorous activity (MVPA); (C) total distance traveled in a wheelchair (DIST_TOT) and distance traveled actively in a wheelchair (DIST_ACT); and (D) laterality (LAT) and mean velocity (VEL) for all in-patient rehabilitation stages (very acute (VA−2 weeks after injury), acute I (A I−4 weeks after injury), acute II (A II−3 months after injury), acute III (A III−6 months after injury), as well as for the out-patients (> 6 months after injury). The horizontal dashed lines depict the ICC level of 0.8, which was chosen as a requirement for a reliable measurement. Solid and dotted lines indicate the confidence intervals. Indicated patient numbers n are the pooled numbers.

Figure 4

ICC values representing the single-day reliabilities for activity counts (AC), time spent in sedentary activity (SED), low physical activity (LPA), moderate-to-vigorous activity (MVPA), total distance traveled in a wheelchair (DIST_TOT), distance traveled actively in a wheelchair (DIST_ACT), laterality (LAT), and mean velocity during active wheeling (VEL) for wheelchair-dependent paraplegic patients (full circle, solid lines) compared to wheelchair-dependent tetraplegic patients (empty circle, dotted lines) for the in-patients (from 2 weeks after injury to 6 months after injury) and out-patients (> 6 months after injury). The dashed horizontal lines depict the ICC level of 0.8, which was chosen as a requirement for a reliable measurement. Solid and dotted lines indicate the confidence intervals. Indicated patient numbers n are the pooled numbers.

Figure 5

The subfigures on the left side (A: in-patients, C: out-patients) represent the number of measurement days needed in order to achieve a reliability of 0.8 for different metrics of movement quantity (activity counts – AC, time spent in sedentary activity – SED, in low physical activity – LPA, in moderate-to-vigorous activity – MVPA, total distance wheeled – DIST_TOT, and distance wheeled actively – DIST_ACT) as well as metrics of movement quality (laterality – LAT and mean wheeling velocity – VEL). Additionally, the numbers of measurement days needed for a reliability of 0.5 and 0.75 are presented with magenta and blue vertical bars, respectively. The subfigures on the right side (B: in-patients, D: out-patients) show the reliabilities, which would be achieved when measuring 3 and 7 days, respectively.

Figure 6

Boxplots for total distance traveled in a wheelchair (A) and mean velocity during active wheeling (B) during weekdays vs. weekends in all single in-patient stages (VA, AI, AII, AIII), as well as out-patients. ^*/⁺ denotes p-value of < 0.05, ^**/⁺⁺ a p-value of < 0.01, ^***/⁺⁺⁺ a p-value of < 0.001, respectively. P-values were calculated using the TOST procedure for normally distributed data (^*), respectively, the adapted equivalence test based on the Mann-Whitney-Wilcoxon Test for non-normally distributed data (⁺).