Motor Planning and Response Selection after Anterior Cruciate Ligament Reconstruction
My colleagues and I have a new paper in the American College of Sports Medicine’s Journal: Medicine & Science in Sports & Exercise.
The Summary
What’s the context?
With a large body of evidence suggesting that individuals with ACL injury have slowed reaction time, slowed neuromuscular activation, and slowed rate of torque development, we set out to identify the source of these impairments in the brain.
What did we find?
Using a choice reaction time paradigm, we found that those with ACLR demonstrated bilateral inhibition of response selection and motor execution processes, committed more errors, and reported greater cognitive challenge than controls. We found no differences between involved and uninvolved limbs in brain activity or errors, suggesting bilateral impairments in those with ACL reconstruction.
What does it mean?
Persistent brain inhibition negatively influence motor planning and motor control following ACLR. These findings suggest individuals with ACL reconstruction overcome inhibition to retain reaction time speed, but achieve this with smaller lateralized brain activation and more errant response selection. We speculate that poorer decision making in the presence of a “speed-accuracy” trade-off may stem from inability to appropriately isolate a motor plan, which has direct implications for rehabilitation and return to function. Physical therapists and athletic trainers should consider therapeutic techniques that improve cortical excitability (e.g., biofeedback) and decision-making (e.g., neurocognitive training).
The Highlights
Task and Stimulus Paradigm.
Stimuli depicting a soccer player and ball were presented for 500ms. Participants responded as quickly as possible by kicking with the left or right foot as determined by the position of the ball. Participants were told to pass the ball to their teammates only.
Reaction Time & Error Rates
Those with ACLR committed 2-3x more errors during “Go” and “NoGo” conditions, but responded at the same speed as controls.
Lateralized Readiness Potential
We generated a “lateralized readiness potential” to indicate brain activation associated with limb movement. By locked activity to the stimulus, we get a sense of motor planning activity (response selection). By locking activity to the response, we get a sense of motor response execution.
Inhibited Motor Planning
Those with ACLR had smaller stimulus-locked activation than controls, indicating inhibition of motor planning processes.
Inhibited Motor Response
Those with ACLR had smaller response-locked activation than controls, indicating inhibition of motor response processes.
Higher Neurocognitive Demands
Those with ACL reconstruction also reported the reaction time task was more demanding overall. This effect was driven by mental, temporal (rushed for time), and effort sub-domains.
The Clinical Bottom Line
Less brain activation underlying motor-planning and response execution neural processes in those with ACLR suggest motor inhibition and difficulty isolating appropriate motor plans. Clinicians should incorporate neurocognitive training (to address motor planning impairments) and modalities that reduce cortical inhibition. By “priming” motor pathways with eccentric crossed exercise, biofeedback, and motor imagery we can increase corticospinal excitability and may be able to address these impairments.
The Full Text
The full paper is available online at MSSE. You can also reach out to me on ResearchGate.
This research was supported by:
the Clinical Sports Medicine Endowment from the American College of Sports Medicine Foundation.
