Table 4.

Features calculated for each time window (3, 5 and 11 s) based on x-, y- and z-axis accelerometer and gyroscope data. Equations adapted from [3,8,9,17,22,23].

Feature	The Number of Features	Equations/Description #
Minimum value	6	Minimum value of all window values
Maximum value	6	Maximum value of all window values
Median	6	Median value of all window values
Upper quartile	6	Upper quartile value of all window values
Lower quartile	6	Lower quartile value of all window values
Kurtosis	6	Kurtosis calculated from window values
Skewness	6	Skewness calculated from window values
Range	6	$Max-Min$
Mean	6	$\frac{1}{n}{{\displaystyle \sum }}_{i=1}^{n}X\left(i\right)$
Variance	6	$\frac{1}{n-1}{{\displaystyle \sum }}_{i=1}^n{\left(X_i-\overline{X}\right)}^2$
Standard deviation	6	$\sqrt{\frac{1}{n-1}{{\displaystyle \sum }}_{i=1}^n{\left(X_i-\overline{X}\right)}^2}$
Root mean square (RMS)	6	$\sqrt{\frac{1}{n}{{\displaystyle \sum }}_{i=1}^n{X}_i{}^2}$
Signal magnitude area (SMA)	2	$\frac{1}{n}{{\displaystyle \sum }}_{i=1}^n\left(\left|X_i\right|+\left|Y_i\right|+\left|Z_i\right|\right)$
Energy	2	$\frac{1}{n}{{\displaystyle \sum }}_{i=1}^n{\left(X_i{}^2+Y_i{}^2+Z_i{}^2\right)}^2$
Entropy	2	$\frac{1}{n}{{\displaystyle \sum }}_{i=1}^n\left(1+{\left(X_i+Y_i+Z_i\right)}^2\right)\ln \left(1+{\left(X_i+Y_i+Z_i\right)}^2\right)$
Dominant frequency	6	After applying Fourier transformation, this is the frequency at which the signal has its highest power
Spectral energy	6	$\frac{1}{N}{{\displaystyle \sum }}_{k=1}^N{\left(F\left(k\right)\right)}^2$ $;N=\frac{n\ast f}{2}$
Spectral entropy	6	$-1\times {{\displaystyle \sum }}_{k=1}^N(\frac{F\left(k\right)}{Z_{1}N}{\mathit{log}}_2\frac{F\left(k\right)}{Z_{1}N})$ $;Z_1=\frac{1}{N}{{\displaystyle \sum }}_{k=1}^{N}F\left(k\right)$
Vectorial dynamic body acceleration (VeDBA)	15	$\sqrt{a_x{}^2+a_y{}^2+a_z{}^2}$
Features of VeDBA		Minimum value, maximum value, median, upper quartile, lower quartile, kurtosis, skewness, range, mean, variance, standard deviation, RMS, dominant frequency, spectral energy, spectral entropy

^# Where n is the total number of all window values; where N is $\frac{n\ast f}{2}$, f is data collection frequency of the device (20 Hz).