Freezing of gait (FoG) is a walking disturbance in the Parkinson's disease (PD). The freezing ratio (FoG-ratio) is a parameter used to quantify overall freezing severity rather than to assess single freezing episodes. Originally the FoG-ratio was designed to be computed from lower limb acceleration. However, some available measurement systems get their data from a single sensor located elsewhere, e.g. on the lower back.

The objective of our paper is to analyse whether acceleration signals measured on different body locations result in a consistent FoG-ratio.

Eighty-four people with PD and 65 people without neurological disorders completed an instrumented Timed Up&Go Test (iTUG) twice. The FoG-ratios from inertial units placed on the chest, lower back, left and right lower limbs were calculated.

There were significant differences between the tested FoG-ratios in the control group as well as in the PD group for both segments. Four significant, but not consistent, correlations were revealed for the turn segment in the PD group. Eight correlations were revealed in the control group. The inter-trial reliability of all the tested cases for gait was good (rho>0.75) but only in one case for turning.

In conclusion, the placement of sensors affected the FoG-ratio parameter output. The different FoG-ratios reflect different amounts of power in the locomotion band of body segments. This could result in inconclusive validity and incomparability of freezing severity presented in studies when the sensor is placed somewhere other than on the lower limbs.