The coefficient of friction in Parkinson's disease gait

This study aimed to characterize the coefficient of friction (COF) curves of patients with Parkinson's disease (PD) during barefoot gait and to evaluate the relationships between this variable and functional scales. Twenty-two subjects with PD (ON phase of levodopa) and 22 healthy subjects participated in this study. The participants walked barefoot along a pathway that went over two force plates embedded in the floor of the data collection room. The instantaneous COF was calculated as the ratio between the horizontal and vertical components of the ground reaction forces. Two-sample t-tests applied to every 1% of the support phase of the COF curve were used to compare the groups and to identify the phases in which the two groups were different. Specifically, three COF areas were computed: Area 1 (for the loading response phase), Area 2 (for the midstance phase) and Area 3 (for the terminal stance phase). Pearson's tests were applied to assess the associations between the COF curve areas and the clinical scales. The subjects with PD exhibited lower COF values during the loading response and terminal stance phases and higher COF values during the mid-stance phase compared with the control group. A strong positive correlation was observed between Area 1 and the Timed Up and Go Test (90.3%). In conclusion, the patients' COFs exhibited patterns that were different from those of the control group. Moreover, during the loading response phase, these differences were well-correlated with the Timed Up and Go Test scale data; Timed Up and Go Test data can be used to identify the risk of falls among PD patients.