Table 1.

Feature development. Candidate features developed to describe the three biomechanical descriptors used in this study: posture (#1), movement intensity (#2 to #5), and movement periodicity (#6 to #9)

S.No.	Biomechanical descriptor	Feature name	Feature description	Computation
1.	Posture	meanRoll	Mean of data from roll axis	$\frac{{\mathrm{\Sigma }}_N{m}_{\mathit{\text{roll}},w}}{N}$	(1)
2.	Intensity	stdRoll	Standard deviation of data from roll axis	std(mroll, w)	(2)
3.		meanAbsDiffRoll	Mean of absolute values of time-differentiated roll data	$\frac{{\mathrm{\Sigma }}_N\left|\frac{d}{\mathit{dt}}\left(m_{\mathit{\text{roll}},w}\right)\right|}{N}$	(3)
4.		axMaxMeanAbsDiff	Maximum, across axes, of mean of absolute values of time-differentiated data from each axis	$\underset{\mathrm{A}\in \text{roll},\text{pitch},\mathrm{yaw}}{max}\left(\frac{{\mathrm{\Sigma }}_N\left|\frac{d}{\mathit{dt}}\left(m_{A,w}\right)\right|}{N}\right)$	(4)
5.		avgMeanAbsDiff	Mean, across axes, of mean of absolute values of time-differentiated data from each axis	$\sum _{A\in \mathit{\text{roll}},\mathit{\text{pitch}},\mathit{yaw}}\frac{{\mathrm{\Sigma }}_N\left|\frac{d}{\mathit{dt}}\left(m_{A,w}\right)\right|}{3N}$	(5)
6.	Periodicity	rollFftPeakPower	Maximum squared coefficient of Fourier transform of data from roll axis	$\underset{\mathrm{i}\in 1\dots \mathrm{L}}{max}\left(c_{f_i,\mathit{\text{roll}},w}^2\right)$	(6)
7.		avgFftPeakPower	Mean, across axes, of maximum squared coefficient of Fourier transform of data from each axis	$\underset{\mathrm{i}\in 1\dots \mathrm{L}}{max}\left(\frac{c_{f_i,\mathit{\text{roll}},w}^2+c_{f_i,\mathit{\text{pitch}},w}^2+c_{f_i,\mathit{yaw},w}^2}{3}\right)$	(7)
8.		rollDiffFftPeakPower	Maximum squared coefficient of Fourier transform of time-differentiated roll data	$\underset{\mathrm{i}\in 1\dots \mathrm{L}}{max}\left({\delta }_{f_i,\mathit{\text{roll}},w}^2\right)$	(8)
9.		avgDiffFftPeakPower	Mean, across axes, of maximum squared coefficient of Fourier transform of time-differentiated data from each axis	$\underset{\mathrm{i}\in 1\dots \mathrm{L}}{max}\left(\frac{{\delta }_{f_i,\mathit{\text{roll}},w}^2+{\delta }_{f_i,\mathit{\text{pitch}},w}^2+{\delta }_{f_i,\mathit{yaw},w}^2}{3}\right)$	(9)

Features were computed on each two-second window w containing N = 200 calibrated triaxial magnetic field intensity values recorded along the roll (m_roll), pitch (m_pitch), and yaw (m_yaw) axes. Equation numbers are indicated on the right