Watch Your Step! Evidence for an intricate relationship between rapid stepping responses and postural control during step initiation

In daily life, we are consistently exposed to visual stimuli that require rapid stepping responses, for example when walking on uneven terrain in a forest or when having to avoid a sudden obstacle in our path (such as the neighbor’s cat). This ability to flexibly interact with our environment requires the interplay between reflexive stepping movements and postural control, which enables us to complete the movement quickly but safely. 

In a collaboration between the Radboudumc (department of Rehabilitation) and Western University in London, Canada, researchers Lucas Billen, Brian Corneil and Vivian Weerdesteyn recently investigated the interplay between rapid step initiation and postural control. The results were published in Neuroscience on 12 September 2023. 

In recent years, our ability to rapidly interact with our environment has been studied in reaching via the measurement of express visuomotor responses (EVRs). EVRs are reflexive bursts of muscle activity that aid in the rapid initiation of a goal-directed movement. You can think of EVRs like express saccades, but for limb muscles. EVRs attest to a sensory-to-motor transformation that rapidly links vision to action within 100ms or less. They have predominantly been studied in reaching, but being able to rapidly initiate steps is also important. In this study, the researchers were interested in EVR expression in the lower limbs when initiating a rapid step to a visual target. Furthermore, they investigated the interaction with potentially competing postural control processes involved in stepping.

To study this, the postural demands of the upcoming step were manipulated. When postural demands were low, strong EVRs in the hip abductor muscle gluteus medius facilitated a rapid stepping response. Yet, under high postural demands, postural control was much more important, so EVRs were generally suppressed, in order to prioritize balance over speed. On occasional instances where EVRs were still present in this high postural demand condition, they actually hindered a fast stepping response.

These results help in the understanding of the interaction between ultra-rapid visuomotor transformations in the EVR network, the postural demands of a given stepping task, and subsequent step initiation. This is also a great starting point for follow-up studies that investigate the same interaction in clinical populations. For example, the research group currently investigates lower-limb EVR expression and postural control in patients with Parkinson’s Disease.

Read the study here

Billen, L. S., Corneil, B. D., & Weerdesteyn, V. (2023). Evidence for an Intricate Relationship Between Express Visuomotor Responses, Postural Control and Rapid Step Initiation in the Lower Limbs. Neuroscience. https://doi.org/10.1016/j.neuroscience.2023.07.025