Concurrent validity of Protokinetics movement analysis software for estimated centre of mass displacement and...

The possibilities of out-of-lab gait analysis are ever increasing, with a recent development from Protokinetics movement analysis software (PKMAS) which, among other parameters, proposes an estimation of centre of mass (COMe) displacement. This measure can be useful in both clinical and sports performance environments.

Does PKMAS provide an accurate estimation of the COM displacement and velocity?

Fifteen participants completed 10 walking trials over the Zeno™ Walkway while simultaneously being equipped with a full-body marker set for VICON analysis. The antero-posterior and medio-lateral COMe displacement components from PKMAS were compared with the projected 3D COM obtained from marker tracking using Bland-Altman analyses and Lin's concordance coefficient. COM velocity was also calculated from the estimated displacement data from PKMAS.

Results demonstrated a high mean bias in both the anteroposterior (AP) and mediolateral (ML) directions for COMe displacement. COMe velocity showed low mean bias but high limits of agreement and low precision. Lin's concordance correlation coefficient showed good to excellent agreement in the AP direction for velocity and displacement, respectively; poor agreement was seen in the ML direction.

Based on these observations, the COMe proposed by the Protokinetics software does not produce accurate results and is to be used with caution in healthy subjects; it is not recommended for subjects presenting pathological gait.