Parkinson's disease (PD) is a neurodegenerative disease, which is characterized by tremor, muscle rigidity and bradykinesia, what may affect the posture and the body balance. The balance disturbance may occur during both: the quite standing and during gait initiation. The aim of this study was to investigate the postural instability in PD patients in different conditions during gait initiation.

The research was conducted on 17 patients with PD in a III clinical stage of disease and 17 older healthy adults – the control group. The gait initiation was measured on the two force platforms. The procedure consisted of three phases: quite standing on a first platform, crossing on the second platform, quite standing on a second platform. There were four conditions: crossing without obstacle, crossing the obstacle, walking up on the step and walking down of the step. We analyzed: phase time 2 [s], stability time S1 [s] (time from loss of stability to step on the second platform), stability time S2 [s] (time from step on the second platform until the stability is regained).

The time phase 2 significantly increased among conditions in both groups (PD: P = 0.0163, control: P = 0.000). In PD group data indicate notable stability problems during walking up on the step, but the elderly have more problems with walking down of the step. The control group presents significant trouble with regained stability after crossing the obstacle and walking up and down of the step ( P = 0.000), while the PD group have equally problem to restore balance in all conditions, even during level ground walking ( P > 0.05). All measured variables were significantly lower in the control group compared to PD group ( P < 0.05).

The different constraints may change the gait initiation patterns in PD patients more than in elderly.