Moving standard deviation of trunk acceleration as a quantification index for physical activities: Validation study (Preprint)

BACKGROUND Step count is often used to quantify activity in individuals using accelerometers. However, slow and irregular gait patterns in the elderly or patients with motor impairments can hinder accurate step detection. Alternative device-specific measures of physical activity exist, but their specificity limits cross-applicability between different device sensors. Moving standard deviation of acceleration (MSDA), obtained from truncal acceleration measurements, is proposed as another alternative parameter to quantify physical activity in patients. OBJECTIVE This study aims to evaluate the effectiveness of MSDA in quantifying physical activity in patients with stroke-induced hemiparesis compared to the traditional step count. METHODS We enrolled 197 consecutive patients with stroke hemiparesis admitted to the recovery rehabilitation ward. Using the Hitoe system, a smart clothing-based truncal acceleration measurement system, we measured MSDA of trunk movement and step count. The correlation between MSDA and step count was examined across all participants. Based on their daily living mobility levels, measured using the mobility score of the Functional Independence Measure (FIM), participants were categorized into six subgroups: FIM1-4, FIM5 (wheelchair), FIM5 (walking), FIM6 (wheelchair), FIM6 (walking), and FIM7 (walking). Inter-subgroup differences in MSDA were analyzed. RESULTS A strong correlation was observed between MSDA and step count (r = 0.78, p < 0.001), with a stronger correlation in the walking group (r = 0.79, p < 0.001) compared to the wheelchair group (r = 0.55, p < 0.001). The Shapiro-Wilk test, supported by an analysis of skewness and kurtosis, indicated that within the subgroups, the distribution of MSDA more closely resembled a normal distribution compared to that of the step count. MSDA corresponded with the independence level indicated by the FIM mobility score, while step count was more influenced by the mode of mobility (wheelchair vs walking). CONCLUSIONS The results suggest the validity of MSDA as a parameter for physical activity in patients with stroke. MSDA is potentially applicable to patients with motor impairments, irrespective of their mobility measures, supporting its wide use in rehabilitation clinical practice.