Reliability and validity of the inertial sensor-based Timed "Up and Go" test in individuals affected by stroke

Abstract--The instrumented Timed "Up and Go" test (iTUG) has the potential for playing an important role in providing clinically useful information regarding an individual's balance and mobility that cannot be derived from the original single-outcome Timed "Up and Go" test protocol. The purpose of this study was to determine the reliability and validity of the iTUG using body-fixed inertial sensors in people affected by stroke. For test-retest reliability analysis, 14 individuals with stroke and 25 nondisabled elderly patients were assessed. For validity analysis, an age-matched comparison of 12 patients with stroke and 12 nondisabled controls was performed. Out of the 14 computed iTUG metrics, the majority showed excellent test-retest reliability expressed by high intraclass correlation coefficients (range 0.431-0.994) together with low standard error of measurement and smallest detectable difference values. Bland-Altman plots demonstrated good agreement between two repeated measurements. Significant differences between patients with stroke and nondisabled controls were found in 9 of 14 iTUG parameters analyzed. Consequently, these results warrant the future application of the inertial sensor-based iTUG for the assessment of physical deficits poststroke in longitudinal study designs. Key words: assessment, balance, inertial sensors, instrumented Timed "Up and Go" test, mobility, motor function test, rehabilitation, stroke, test-retest reliability, validity. INTRODUCTION After a stroke, many individuals experience hemipa-resis, which often leads to an impaired walking pattern with altered gait characteristics [1-7]. Specifically, hemi-plegic gait is typically associated with a reduced gait speed [1-3,5,8], cadence [2,5,8], and stride length [2,8] and an increased left-right asymmetry during walking [1,3,9] when compared with nondisabled, age-matched controls. Furthermore, it is often characterized by an increased stance phase duration [2]. Hemiparesis not only leads to gait impairments but may also affect balance and postural transfers (i.e., changing position from sitting to standing and vice versa), further impeding the patients' mobility and independence [6,10-12]. It is therefore a central goal of stroke rehabilitation to improve the patient's independence and functional capacity by improving his or her mobility [13]. The Timed "Up and Go" test (TUG) is often used, with good reliability and validity, to evaluate balance and mobility in patients with stroke [14-17]. The TUG requires a person to rise from a chair, walk a distance of 3 m at a self-paced, comfortable speed, turn around, and return to the chair to sit down again. The total time for completion is recorded and used as a measure of mobility. However, although the TUG is commonly used to evaluate mobility poststroke, it has some drawbacks. First, it only uses the outcome parameter "time" and fails to detect other balance- and mobility-related parameters [18-19]. Second, although it consists of a number of consecutive tasks, it does not allow analysis of these tasks separately [18-19]. Recently, several researchers instrumented the TUG in an effort to overcome some of the drawbacks. For example, Vernon et al. used a Microsoft Kinect camera-based TUG method for analyzing the specific subcomponents of the test [20]. Furthermore, Zampieri et al. revealed the potential benefit of an instrumented TUG (iTUG) system using wearable inertial sensors while assessing individuals with Parkinson disease (PD) [19]. While 10 of the 21 gait and postural transition parameters that were identifiable with the iTUG showed significant differences between individuals with PD and nondisabled controls, the total test performance time was not diverging. Obviously, the iTUG seemed to exhibit a greater sensitivity than the conventional TUG in terms of mobility deficit detection in individuals with PD [18]. The recent use of body-fixed sensors suggests that they could serve as a tool for analyzing measures of physical functioning of patients [21-22]. …