Table 4.

Description of the extracted features for each step from the accelerometer (A) and/or the gyroscope (G). For each step, 50 features from the time and frequency domains are computed.

Feature Name	Sensor	Axis	Total	Description
Step Length	A	x	1	Total number of frames
Step Duration (s)	A	x	1	Step duration in seconds
Average	A, G	x, y, z	6	Mean value of the step
Standard Deviation	A, G	x, y, z	6	σ of the step
Minimum	A, G	x, y, z	6	Global minimum of the step
Maximum	A, G	x, y, z	6	Global maximum of the step
Root Mean Square	A, G	x, y, z	6	RMS value of the step
Entropy	A, G	x, y, z	6	Uncertainty measure of the step, $s_i$.: $-{\sum }_{i=1}^n\left(p_i\right)lo{g}_2\left(p_i\right)$ where $p_i=\frac{\frac{s_i}{max\left(s_i\right)}}{{\sum }_{i=1}^n\frac{s_i}{max\left(s_i\right)}}$
Signal Energy	A, G	x, y, z	6	Energy of the step: ${\sum }_{n=1}^N{\left|x\left[n\right]\right|}^2$
Amplitude	A, G	x, y, z	6	Maximum amplitude of the frequency spectrum of the signal of the step