Step-length obstacle synergy found to be lower in Parkinson’s patients

A multidisciplinary research group affiliated with the Laboratory for Human Movements of the Department of Physical Education (Movi-Lab) at the State University of Sao Paulo (UNESP) in Bauru, Brazil, measured stride length synergies as it overcame obstacles in patients with Parkinson’s disease and concluded that this is 53% lower than in healthy subjects of the same age and weight. Step length is one of the main variables affected by the disease.

Synergy, defined as combined work, refers in this case to the ability of the locomotor (or musculoskeletal) system to adapt movement when crossing an obstacle, combining for example factors such as speed and foot position. Improving synergies in Parkinson’s patients while walking can significantly affect their quality of life, as they fall on average three times more often than healthy people of the same age.

There are patients in our exercise group who fall three or four times a week. It is important to understand how the gait and movement of these patients adjust as they cross obstacles so that we can improve the synergy of stride length. This approach allows us to perfect the exercise protocol, improve movement and try to reduce the frequency of falls. “

Fabio Augusto Barbieri, Professor, UNESCO Department of Physical Education and his postgraduate program Movement Science

An article about the study was published in a journal Gait and posture. Barbieri is the last author. The first author is mechanical engineer Satyajit Ambike, a professor in the Department of Health and Kinesiology at Purdue University in the United States. The study was the first to report impaired locomotor synergies in Parkinson’s patients.

“The innovation in our study focuses on walking time or rhythm, the consistency with which patients place their feet to maintain movement,” Barbieri said. “This can be assessed by measuring step length synergy. Synergy assumes a goal and is related to the way the locomotor system adapts to achieve it. In our case, we investigated how the system adjusts to achieve the goal of crossing an obstacle during locomotion.”

Researchers have found that Parkinson’s patients are less able to adjust the position of their feet than healthy people as they approach and cross an obstacle. “The locomotor system is always trying to adjust to maintain stability while moving. If there is no stability, we could make mistakes that can lead to a fall,” Barbieri said. “Parkinson’s patients are less constant in setting their feet while walking, and the walking time is unstable as a result. Their speed increases and decreases as they walk, and the length of the steps varies along with the setting of the feet.”


Thirteen Parkinson’s patients and 11 neurologically healthy controls participated in the study. All participants were over 50 years old. To be eligible, they had to walk without assistance, have normal vision and hearing (with or without lenses and hearing aids), have no orthopedic or neurological diseases other than Parkinson’s disease, and be able to understand and follow instructions. Patients took Parkinson’s disease medication (Levodopa) for at least three months prior to data collection.

Participants had to walk through a passage (length 8.5 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. The walking speed is not imposed but is chosen by each participant. No instructions are given as to which leg should cross the obstacle, but its position is adapted to each participant so that the right leg must guide.

“We tried to standardize the task so that all respondents crossed the obstacle leading with their right foot,” Barbieri said. “The idea was to make sure there was no interference from other factors in the way we moved. The height of the obstacle was 15cm, because that’s the standard height of curbs in Brazil. We thought it would be best to stick to the standard.”

Numerous systems must work together for synergy to occur in terms of achieving the goal, he explained. “When the distance between the toes and the obstacle [before it is crossed] and between the heel and the obstacle [after it is crossed] varies greatly, the risk of contact with the obstacle increases. Too close to an obstacle before crossing means that you have to raise the leading leg so high that it can prove impossible. If the accompanying foot goes too close to the obstacle after crossing, the heel is likely to touch it, ”he said, adding that walking time should ideally be constant and the foot should not come too close to the obstacle on either side.


The step length synergy was measured using a methodology derived from mechanical engineering and adapted to the study of human movement. The methodology is not specific for gait analysis or Parkinson’s disease, but is adapted to a set of techniques used by Ambike and Mark Latash of Pennsylvania State University to measure upper limb strength.

Eight motion cameras used in the study were purchased with FAPESP funding (grant no. 2017 / 19516-8). The study was also supported by a grant from a visiting researcher.

Twenty reflective markers were placed according to a specific gait analysis model on the body of each participant in the experiment. “As the subject walks and crosses the obstacle, the cameras emit infrared light reflected by the markers. The cameras record the position of the markers, which allows us to determine the length and duration of the steps. The stroke analysis software does other calculations,” Barbieri explained.

According to Barbieri, this research was first applied to gait analysis. “Another novelty was that we used a single variable to relatively easily detect possible gaps related to walking time, facilitating more consistent future intervention to improve walking time through training,” he said. “This is the point of gait analysis in general. You want to identify possible variables in gait changes and modify the intervention on that basis.”

Since then, the same researchers have begun a study to determine whether obstacle height affects step length synergy. “We want to know if this synergy is changing because the obstacle is bigger or lower. This refers to the environment in which the patient is moving. If there are obstacles of a certain height in that area, they can create problems and lead to falls, so we can modify the environment to make it easier to move, ”Barbieri said.


Establishment of Amparoa from Pesquis do Estado de São Paulo (FAPESP)

Journal reference:

Ambike, S., and others. (2021) The synergy of stride length when crossing obstacles is weaker in patients with Parkinson’s disease. Gait and posture.