with a step size of 0.1 s. The final FI was the average of eight sensor channels that were least contaminated (four on each side, including foot, shank, thigh and waist). A ‘freezing threshold’ was set to ‘3’.21 Notably, because FI is a dynamic measurement, we defined that if FI dropped from >3 to a value between 2 and 3 and then rose back to >3, this was considered as one continuous freezing event rather than two. But if the FI dropped from >3 to a value <2, this marked the end of the freezing. Setting ‘2’ as a ‘lower freezing threshold’ was based on evidence that the lowest individual freezing threshold is around ‘2’.22 The period lasting from the first to the last time point where FI is >3 in a freezing event was referred to as the duration of a freezing event (Fig. 1D). In each trial, the number of freezings and the duration of each freezing event were counted and calculated. In addition, we classified each walking trial as a freezing trial or a non-freezing trial based on whether it contained a freezing event. Only trials with consistent judgements between subjective and objective assessments were qualified for
