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Why Crossing Obstacles Is Difficult for People With Parkinson Disease


Researchers found that people with Parkinson disease have 53% lower step length synergy while crossing obstacles than those without the condition, potentially providing a target approach to address fall risk in patients.

In patients with Parkinson disease (PD), impaired movement stability characterized by postural and gait instability is a common symptom that can lead to falls and mishandled objects.

Quantified by the term synergy, which is the capacity of the locomotor or musculoskeletal system to adapt movement while crossing an obstacle, a multidisciplinary research group affiliated with the Department of Physical Education’s Human Movement Laboratory at São Paulo State University (UNESP) in Bauru, Brazil, note that the decline in synergistic stabilization has been observed in prior analyses of manual and postural tasks among those with PD.

However, they say that locomotor synergies, such as speed and foot position, have yet to be studied in patients with PD, which may influence fall risk.

“There are patients in our exercise group who fall 3 or 4 times a week. It’s important to understand how these patients’ gait and locomotion adapt while crossing obstacles so that we can improve step-length synergy,” said study author Fabio Augusto Barbieri, professor at the Department of Physical Education and Movement Science Graduate Program at the São Paulo State University (UNESP) in Bauru, Brazil, in a statement.

In the study, published recently in Gait & Posture, researchers recruited 13 patients with PD and 11 healthy age-matched controls, all over the age of 50 years, to walk along a gangway (length, 8.5 meters (m); width 3.5 m), and cross a foam rubber obstacle (height 15 cm; width 60 cm; depth 5 cm) placed 4 m from the starting point for 15 times.

“We tried to standardize the task so that all the subjects crossed the obstacle with their right leg leading,” said Barbieri. “The idea was to ensure there was no interference from other factors in the locomotion pattern. The height of the obstacle was 15 cm because that’s the standard curb height in Brazil. We thought it would be best to stick to the standard.”

During the crossing step, researchers measured the distances of the rear and front foot toes from the obstacle, utilizing the uncontrolled manifold method to assess the across-trial variance in toe distances into a component that maintains the step length and a component that changes the step length.

With this methodology applied for the first time to analyze gait stability, they explained that these variance components yielded the synergy index that could then show the stability of step length.

In their findings, step length was stabilized in both subject groups, although those with PD were found to exhibit a synergy index 53% lower than the control group.

Noting that the locomotor system works to adapt so as to maintain constancy while moving, Barbieri says that the lack of constancy for those with PD can cause patients to make mistakes that then lead to a fall.

“Patients with PD are less constant in positioning their feet while walking, and gait timing tends to be unstable as a result. Their speed rises and falls as they walk, and step length varies along with foot placement,” added Barbieri.

Following study findings, the same research group have begun a study to examine whether obstacle height may also affect step-length synergy.


Ambike S, Penedo T, Kulkarni A, Santinelli FB, Barbieri FA. Step length synergy while crossing obstacles is weaker in patients with Parkinson’s disease. Gait Posture. Published online January 8, 2021. doi:10.1016/j.gaitpost.2021.01.002

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