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 HX711 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.

中文翻译：

---

带有开源软件的数字浴室磅秤可提供有效的动态地面反作用力数据，以进行评估和生物反馈

背景

测量动态垂直地面反作用力可以评估重要的临床和物理能力因素，例如负重不对称，力分布和力发展速度。但是，当前用于精确评估地面反作用力的技术通常很昂贵。

研究问题

这项研究的目的是检验从低成本的改进型数字浴室磅秤获得静态和动态地面反作用力数据的有效性和可靠性。

方法

检查了四个改进的浴室秤，两个不同品牌的两个单元。使用0.01至65 kg的已知载荷进行了重复的机械载荷试验，并将获得的数据与已知载荷进行比较，以计算精度，磁滞和非线性。32位成年人进行了5次坐着站和体重转移的动态试验。进行绝对和相对一致的类内相关系数，以及Pearson和Spearman的相关性，以确定力学测试的有效性和可靠性。为每个比较创建Bland-Altmann图。对动态数据执行平均绝对误差（MAE）和无偏互相关，将校准数据与Bertec力平台的已知值进行比较。

结果

磁滞和非线性性能优异（满量程<0.2％），机械测试结果显示出极好的可靠性和有效性。动态数据的互相关结果非常好，但是，从站立到站立的较快速任务的MAE高于较慢的举重测试。这可能是由于HX711放大器的最低噪声设置（10 Hz）的默认采样率较低所致。

意义

总而言之，我们的结果表明，可以轻松，廉价地对数字浴室磅进行修改，以获得准确的垂直地面反作用力数据，并且灵敏度低至0.01 kg。