Principles of motor learning to support neuroplasticity after ACL injury: implications for optimizing performance and reducing risk of second ACL injury

Key points

1. 01Only around 55% of post-ACLR patients return to competitive sport, and up to 20-23% of young athletes who return to sport experience a second ACL rupture within the first year
2. 02ACL injury causes measurable brain changes including altered intracortical facilitation and inhibition that current rehabilitation programs do not sufficiently address
3. 03External focus of attention instructions (directing attention to movement effects on the environment rather than the body) improve motor performance and neuroplastic responses more than internal focus instructions
4. 04Implicit learning methods using analogies rather than explicit step-by-step instructions reduce working memory load and promote more automatic movement control that is more robust under competitive pressure
5. 05Self-controlled feedback schedules and differential learning (introducing controlled movement variability) further support neuroplasticity and long-term motor skill retention

How it was conducted

Design

Narrative review with integrated clinical framework

Topic

Application of motor learning principles to ACL rehabilitation and second injury prevention

Key concepts reviewed

External focus of attention, implicit learning, differential learning, self-controlled learning, and contextual interference

Outcome focus

Neuroplasticity, motor skill acquisition, functional performance, and second ACL injury risk

Population

Athletes and patients undergoing ACL reconstruction rehabilitation

What they found

• Adopting an external focus of attention increases intracortical inhibition within the primary motor cortex (Kuhn et al., Acta Physiol, 2017), which may restore quadriceps activation deficits associated with ACL injury
• Corticospinal and intracortical excitability differ between athletes early after ACLR and matched controls (Zarzychi et al., J Orthop Res, 2018)
• Greater intracortical inhibition associates with lower quadriceps voluntary activation in individuals with ACL reconstruction (Luc-Harkey et al., Exp Brain Res, 2017)
• Self-control participants in an EEG study had better accuracy on transfer of a newly acquired motor skill compared to yoked participants, indicating neuroplasticity linked to behavioral gains
• Simple decision rules based on return-to-sport criteria can reduce reinjury risk by 84% after ACL reconstruction (Grindem et al., Br J Sports Med, 2016)

Limitations

• This is a narrative review without systematic search or meta-analytic synthesis, so findings reflect the authors' interpretation rather than pooled effect sizes
• Direct RCT evidence specifically testing the combined motor learning framework in post-ACLR populations is lacking, and most supporting evidence is drawn from non-ACL motor learning studies
• The neural correlates and neuroplasticity mechanisms described are largely inferred from indirect evidence and small laboratory studies
• Optimal dosing, timing, and sequencing of these motor learning principles within ACL rehabilitation protocols have not been established

Why it matters

For patients

Patients recovering from ACL surgery should know that how exercises are instructed and practiced matters as much as what exercises are done, and that rehabilitation focused on automatic, externally-cued movement may lower the chance of tearing the ACL again.

For clinicians

Clinicians can begin shifting rehabilitation language toward external focus cues, incorporate analogy-based and variable practice, and offer self-controlled feedback to better address the brain-level deficits that persist after ACLR and contribute to re-injury.

For readers

This paper provides a theoretical and practical framework for integrating motor learning science into ACL rehabilitation, bridging neuroscience and clinical practice to address one of the most persistent problems in sports medicine, namely the high rate of second ACL injuries.