Validity of the detection of wheelchair propulsion as measured with an Activity Monitor in patients with spinal cord injury

Study design: Validation study. Objectives: An accelerometry-based Activity Monitor ( AM) has proven to be a valid instrument to quantify mobility-related activities ( lying, sitting, standing, walking, cycling, general (noncyclic) movement). The aim of this study was to assess whether, additional to other activities, wheelchair propulsion ( hand-rim wheelchair propulsion and handbiking) can be validly detected by the AM in patients with spinal cord injury (SCI). Setting: Rehabilitation center. Methods: In all, 10 patients with SCI ( aged 19 - 63 years; five patients with poor triceps strength and five patients with good triceps strength) participated. Patients performed a series of representative daily life activities ( involving wheelchair propulsion and nonwheelchair propulsion activities), according to a standard protocol, in a seminatural setting. Continuous registrations of signals from body-fixed accelerometers were made and the AM output ( after automatic analysis) was compared with visual analysis of simultaneously made video recordings ( reference method). Validity scores ( agreement, sensitivity, specificity) between the output of the AM and the video analysis were calculated. Results: Agreement, sensitivity and specificity for the detection of wheelchair propulsion were overall 92 ( range, 87 - 96)%, 87 ( 76 - 99)% and 92 ( 85 - 98)%, respectively. Sensitivity was smaller in patients with poor triceps strength compared to patients with good triceps strength; 81 ( 76 89)% and 95 ( 89 - 99)%, respectively (P<0.01). Mean overestimation in duration of wheelchair propulsion by the AM was 3.9% (P<0.05). Conclusion: Besides already validated other activities, wheelchair propulsion (hand-rim wheelchair propulsion and handbiking) can be validly detected by the AM in patients with SCI, both with good and poor triceps strength. Therefore, the AM offers the possibility to obtain objective and detailed information on all major mobility-related activities performed by patients with SCI.