In 2022, my colleagues and I published a paper in the American College of Sports Medicine’s Journal: Medicine & Science in Sports & Exercise. (The first is discussed in this blog post.)

The Summary

What’s the context?

Individuals with ACL injury have quadriceps muscles weakness and activation failure. These impairments are relatively unresponsive to strength & conditioning — Many believe that the quality of the connection between the motor cortex and the quadriceps muscle may be damaged or deconditioning due to inhibition. We used a technique called corticomuscular coherence to measure the quality of this connection in an effort to identify the source of these impairments in the brain.

What did we find?

Using a force tracing paradigm, we found that those with ACLR demonstrated poorer quality connectivity between the motor cortex and the quadriceps muscles bilaterally and had quadriceps force control. We found no differences between involved and uninvolved limbs in connectivity, suggesting bilateral impairments in those with ACL reconstruction.

What does it mean?

These results demonstrate reduced neural drive to the quadriceps muscles in individuals with ACLR. Notably, these differences were present only in the gamma frequency coherence band, suggesting impairments may be specific to multisensory integration and force modulation.

The sample also presented with involved limb quadriceps weakness and reduced cortical excitability. Physical therapists and athletic trainers should consider therapeutic techniques that improve cortical excitability (e.g., biofeedback) and spinal-level excitability (e.g., cyrotherapy) while isolating the quadriceps during strength training with open kinetic chain exercise.

The Highlights

The Clinical Bottom Line

Quadriceps muscle inhibition, activation failure, and weakness are all clinically relevant impairments in rehabilitation of individuals following ACLR. Reduced neural drive to the quadriceps muscles and resultant differences in motor unit behavior (1) underpin these impairments. Although the effects on corticomuscular coherence are unknown, disinhibitory modalities such as eccentric crossed exercise, biofeedback, and motor imagery can prime motor pathways in this population (2-5). When in alignment with patient goals, clinicians should apply these interventions solely for previously reported clinical benefits, as well as mechanistic alignment with cortical and corticomuscular coherence impairments (6). Additionally, visuo-sensory-motor and motor planning processes contribute to the recorded gamma band coherence. 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.

1 - Nuccio et al. J Physiol. 2021.
2 - Bodkin et al. Clin Biomech. 2021.
3 - Luc et al. J Electromyogr Kinesiol. 2016.
4 - Pietrosimone et al. J Electromyogr Kinesiol. 2015.
5 - Lepley et al. J Strength Cond Res. 2012.
6 - Norte et al. J Sport Rehabil. 2021.