skdh.gait_old.PhaseCoordinationIndex

class skdh.gait_old.PhaseCoordinationIndex

Assessment of the symmetry between steps during straight overground gait. Computed for an entire bout, it is a measure of the deviation from symmetrical steps (ie half a stride is equal to exactly 1 step duration). Lower values indicate better symmetry and a “more consistent and accurate phase generation” [2].

Methods

predict(fs, leg_length, gait, gait_aux)

Predict the bout level gait endpoint

Notes

The computation of PCI relies on the assumption that healthy gait is perfectly even, with step times being exactly half of stride times. This assumption informs the definition of the PCI, where the perfect step phase is set to \(180^\circ\). To compute PCI, the phase is first computed for each stride as the relative step to stride time in degrees,

\[\varphi_i = 360^\circ\left(\frac{hs_{i+1}-hs_{i}}{hs_{i+2}-hs{i}}\right)\]

where \(hs_i\) is the ith heel-strike. Then over the whole bout, the mean absolute difference from \(180^\circ\) is computed as \(\varphi_{ABS}\),

\[\varphi_{ABS} = \frac{1}{N}\sum_{i=1}^{N}|\varphi_i - 180^\circ|\]

The coefficient of variation (\(\varphi_{CV}\)) is also computed for phase,

where \(\bar{\varphi}\) and \(s_{\varphi}\) are the sample mean and standard deviation of \(\varphi\) respectively. Finally, the PCI is computed per

\[PCI = \varphi_{CV} + 100\frac{\varphi_{ABS}}{180}\]

References

[1]

M. Plotnik, N. Giladi, and J. M. Hausdorff, “A new measure for quantifying the bilateral coordination of human gait: effects of aging and Parkinson’s disease,” Exp Brain Res, vol. 181, no. 4, pp. 561–570, Aug. 2007, doi: 10.1007/s00221-007-0955-7.

[2]

A. Weiss, T. Herman, N. Giladi, and J. M. Hausdorff, “Association between Community Ambulation Walking Patterns and Cognitive Function in Patients with Parkinson’s Disease: Further Insights into Motor-Cognitive Links,” Parkinsons Dis, vol. 2015, 2015, doi: 10.1155/2015/547065.