The Effect of Exercise on Neuromuscular Performance Post-ACL Tear

What does the ACL do? Joint stabilization Prevents Neural organ anterior translation of tibia excessive internal rotation of tibia knee hyperextension Neural organ

Mechanism of Injury Quick deceleration Hyperextension Rotation Majority of tears involve zero contact with another person “act of God”

Arthrogenic Muscle Inhibition (AMI) likely helping to prevent painful and potentially detrimental movements Treatement  TENS to allow for more motoneurons to be recruited during the voluntary contraction promoting more complete restoration of strength https://uncexss.wordpress.com/2015/04/13/influence-of-vibratory-stimuli-on-neuromuscular-function/ The inability to completely activate a muscle Potential factor contributing to quadriceps weakness Reduced motor drive to muscles surrounding a joint as a possible protection mechanism Occurs bilaterally

Mechanisms of AMI Mechanoreceptors in ACL deliver sensory information to the spinal cord joint movement, joint loading, and joint position After rupture, less excitability of the quadriceps muscles and therefore atrophy Posted with permission

Figure 1.Palmieri-Smith and Thomas’ proposed neural pathway for arthogenic muscle inhibition in the anterior cruciate ligament.

Figure 2. Konishi et al.’s proposed neural pathway for arthrogenic muscle inhibition in the anterior cruciate ligament.

Figure 3. Reduction of arthrogenic muscle inhibition over time.

Treatment Active contractions with TENS/EMS Typical rehab exercises for ACL tears include: lunges, squats, hamstring curls, step ups, single leg bodyweight deadlifts Used in conjunction with TENS/EMS can help activate muscle fibres during these exercises Eccentric contractions have been shown to lessen muscle atrophy

Eccentric contractions Lepley et al. 4 groups, NMES, NMES and E, E, standard protocol without NMES or E NMES and E, and E > NMES alone and standard protocol Eccentric exercises were eccentric repetitions on leg press (4x10, 2 min rest between sets) Intensity was 60% eccentric 1RM

Eccentric contractions choose type II muscle fibre types It is thought that these fibers are inhibited post-surgery Eccentric contractions promote activation of these fibres resulting in greater force production

Implications for Future Rehab Procedures Adding eccentric contractions with neuromuscular stimulation could help reduce arthrogenic muscle inhibition

References American Orthopaedic Society for Sports Medicine. (March 2014). Anterior Cruciate Ligament (ACL) Injuries. Retrieved from http://orthoinfo.aaos.org/topic.cfm?topic=a00549 Konishi, Y., Fukubayashi, T., & Takeshita D. (2002). Mechanism of quadriceps femoris muscle weakness in patients with anterior cruciate ligament reconstruction. Scandinavian Journal Medicine Science Sports, 12, 371-375. Lepley, L. K., Wojtys, E. M., & Palmieri-Smith, R. M. (2015). Combination of eccentric exercise and neuromuscular electrical stimulation to improve quadriceps function post-ACL reconstruction. The Knee, 22, 270-277. Padua, D. A. (2015, April 13). Influence of Vibratory Stimuli on Neuromuscular Function. Retrieved from https://uncexss.wordpress.com/2015/04/13/influence-of-vibratory-stimuli-on-neuromuscular-function/ Palmieri-Smith, R. M. & Thomas, A. C. (2009). A neuromuscular mechanism of posttraumatic osteoarthritis associated with ACL injury. Exercise Sports Science Review, 37, 147-153.