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Digital bathroom scales with open source software provide valid dynamic ground reaction force data for assessment and biofeedback
Journal article   Peer reviewed

Digital bathroom scales with open source software provide valid dynamic ground reaction force data for assessment and biofeedback

Ross Clark, Benjamin Mentiplay, Hong-Han Tan, Louise Bechard, Emma Hough and Yong-Hao Pua
Gait & Posture, Vol.84, pp.137-140
2021
DOI: https://doi.org/10.1016/j.gaitpost.2020.10.023
PMID: 33321409
url
https://doi.org/10.1016/j.gaitpost.2020.10.023View
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Abstract

weightbearing asymmetry knee ground reaction force loading low cost
Background: Measuring dynamic vertical ground reaction force allows for assessment of important clinical and physical capacity factors such as weight bearing asymmetry, force distribution, and rate of force development. However, current technologies for accurately assessing ground reaction force are typically expensive. Research Question: The aim of this study was to examine the validity and reliability of obtaining static and dynamic ground reaction force data from low-cost modified digital bathroom scales. Methods: Four modified bathroom scales, two units each of two different brands, were examined. Repeated mechanical loading trials were performed with known loads ranging from 0.01 to 65 kg, with acquired data compared against the known loading to calculate accuracy, hysteresis, and non-linearity. Dynamic trials consisting of 5 times sit-to-stand and weight-shifting were performed by 32 adults. Absolute and relative agreement intraclass correlation coefficient, and Pearson’s and Spearman’s correlations were performed to determine validity and reliability for the mechanical tests. Bland-Altmann plots were created for each comparison. Mean absolute error (MAE) and unbiased cross-correlation were performed on the dynamic data, comparing the calibrated data to the known values from a Bertec force platform. Results: Hysteresis and non-linearity were excellent (<0.2% full-scale), and mechanical test results showed excellent reliability and validity. Cross-correlation results for the dynamic data were excellent, however MAE for the more rapid sit-to-stand task was higher than the slower weight-shifting test. This may have been due to the low default sampling rate for the lowest noise setting of the amplifier (10 Hz). Significance: In summary, our results suggest that digital bathroom scales can be easily and inexpensively modified to obtain accurate vertical ground reaction force data, with sensitivity to detect changes of as little as 0.01 kg. Measuring weight distribution and asymmetry during standing and functional tasks using vertical ground reaction force (VGRF) data [1] provides clinical information about dynamic balance [2], functional mobility [3], and loading [4]. Importantly, clinical populations may incorrectly perceive symmetry due to weakness, hence the importance of assessment and feedback [5]. The discontinued Wii Balance Board provided reliable [6] and valid [7] VGRF data. As an inexpensive, portable alternative, bathroom scales can be used off-the-shelf to measure static VGRF [8]. Digital bathroom scales typically contain force sensors in each corner, which can be externally amplified to obtain real-time, digitized VGRF data. Previous studies provide limited manufacturer-modified bathroom scale validation [[9], [10], [11]], but to our knowledge no studies have systematically examined the reliability and validity of user-modified, off-the-shelf bathroom scales.

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