Open Access Research

Self-triggered assistive stimulus training improves step initiation in persons with Parkinson’s disease

Robert A Creath1, Michelle Prettyman1, Lisa Shulman2, Marjorie Hilliard3, Katherine Martinez3, Colum D MacKinnon3, Marie-Laure Mille3, Tanya Simuni4, Jane Zhang3 and Mark W Rogers1*

Author Affiliations

1 Department of Physical Therapy & Rehabilitation Science, University of Maryland School of Medicine, 100 Penn Street, Room 115, Baltimore, MD, 21201, USA

2 Department of Neurology, University of Maryland School of Medicine, Baltimore, MD, USA

3 Northwestern University Feinberg School of Medicine, Department of Physical Therapy & Human Movement Sciences, Northwestern University, Chicago, IL, USA

4 Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA

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Journal of NeuroEngineering and Rehabilitation 2013, 10:11  doi:10.1186/1743-0003-10-11

Published: 30 January 2013



Prior studies demonstrated that hesitation-prone persons with Parkinson’s disease (PDs) acutely improve step initiation using a novel self-triggered stimulus that enhances lateral weight shift prior to step onset. PDs showed reduced anticipatory postural adjustment (APA) durations, earlier step onsets, and faster 1st step speed immediately following stimulus exposure.


This study investigated the effects of long-term stimulus exposure.


Two groups of hesitation-prone subjects with Parkinson’s disease (PD) participated in a 6-week step-initiation training program involving one of two stimulus conditions: 1) Drop. The stance-side support surface was lowered quickly (1.5 cm); 2) Vibration. A short vibration (100 ms) was applied beneath the stance-side support surface. Stimuli were self-triggered by a 5% reduction in vertical force under the stance foot during the APA. Testing was at baseline, immediately post-training, and 6 weeks post-training. Measurements included timing and magnitude of ground reaction forces, and step speed and length.


Both groups improved their APA force modulation after training. Contrary to previous results, neither group showed reduced APA durations or earlier step onset times. The vibration group showed 55% increase in step speed and a 39% increase in step length which were retained 6 weeks post-training. The drop group showed no stepping-performance improvements.


The acute sensitivity to the quickness-enhancing effects of stimulus exposure demonstrated in previous studies was supplanted by improved force modulation following prolonged stimulus exposure. The results suggest a potential approach to reduce the severity of start hesitation in PDs, but further study is needed to understand the relationship between short- and long-term effects of stimulus exposure.

Step; Initiation; Parkinson’s; Freezing; Hesitation; Intervention