Quadriceps cortical adaptations in individuals with an anterior cruciate ligament injury

Abstract

Background Altered quadriceps corticomotor excitability has been demonstrated following anterior cruciate ligament (ACL) injury and reconstruction, however only the single joint vasti muscles have been assessed. There is no current data on rectus femoris corticomotor excitability following ACL injury, the biarticular quadriceps muscle also critical for force attenuation and locomotion. The purpose of this study was to examine rectus femoris corticomotor excitability, intracortical inhibition and cortical motor representation in individuals with and without an ACL injury. Methods A cross-sectional design was used to evaluate corticomotor excitability bilaterally in individuals with a physician confirmed ACL injury (12 males, six females; mean ± SD age: 29.6 ± 8.4 years; BMI: 24.8 ± 2.3 kg·m2; 69.5 ± 42.5 days post-injury) compared to a healthy control group (12 males, six females; age: 29.2 ± 6.8 years; BMI: 24.6 ± 2.3 kg·m2). Single-pulse transcranial magnetic stimulation (TMS) was used to assess corticomotor excitability and cortical motor representation, and paired-pulse TMS used to assess intracortical inhibition for rectus femoris while participants maintained a knee extension force at 10% of body weight. Results The cortical silent period (cSP) duration was longer in the injured limb of the ACL group compared to the uninjured limb (P = 0.004). No significant differences were found for corticomotor excitability, intracortical inhibition or cortical motor representation center position and size (P > 0.05). Conclusions There is preliminary evidence that the cSP is longer, but changes in rectus femoris corticomotor excitability and cortical motor representation are not present following ACL injury.