Inclusion Criteria:  For 2 groups :  Man or woman 60-85 years old Informed consent obtained Group Parkinson : clinical diagnosis of idiopathic Parkinson's Disease, according to the UK Brain Bank criteria.  Exclusion Criteria:  For 2 groups :  Assisted walker Neurological (other than those resulting from Parkinson's disease), cardiologic, rheumatologic disorders Disorders affecting gait. Montreal Cognitive Assessment (MOCA) < 24. Concomitant medication likely to interfere with the results.  Group Parkinson:  freezing Hoehn et Yahr > III