Quadriceps Inhibition After ACL Injury: Neuromuscular and Functional Consequences
Quadriceps Inhibition After ACL Injury: Neuromuscular and Functional Consequences
Quadriceps muscle weakness is a common consequence of ACL injury. This muscle weakness is considered to result from neural inhibition preventing full muscle contraction and is referred to as arthrogenic muscle inhibition (AMI). AMI hinders rehabilitation by preventing gains in strength, increasing the risk of re-injury, and potentially placing patients at risk for chronic degenerative joint conditions. Quadriceps weakness that occurs following ACL injury is also thought to be caused by muscle atrophy which is thought to manifest due to alterations in muscle architecture, selective fiber atrophy or even neural deficits such as AMI. Importantly, interventions that are designed to counter this muscle weakness are required in order to promote long-term knee joint health. Hence, the purpose of the current study is to determine the efficacy of interventions that target quadriceps weakness to improve quadriceps muscle function and biomechanics in patients prior to and following ACL reconstruction. Specifically, the efficacy of neuromuscular electrical stimulation aimed at improving quadriceps neural activity and eccentric exercise intended to minimize quadriceps muscle atrophy will be investigated. The investigators expect that patients who receive the electrical stimulation therapy will demonstrate improvements in quadriceps strength and activation. Furthermore, it is expected that patients who receive both the electrical stimulation and eccentric intervention will demonstrate markedly greater gains in quadriceps strength and activation than patients who receive only the electrical stimulation therapy or standard of care post-surgery. The investigators also hypothesize that the patients who receive the electrical stimulation therapy and/or eccentrics will display knee motion similar to uninjured control subjects.
Neuromuscular electrical stimulation (NMES) has been shown to reduce quadriceps activation failure (QAF) and eccentric exercise has been shown to lessen muscle atrophy post-ACL reconstruction. Given thatthese are two critical components of quadriceps strength, intervention combining these therapies may be effective at reinstituting quadriceps function post-reconstruction. Therefore, the aim of this study is to evaluate the effectiveness of a combined NMES and eccentric exercise intervention to improve the recovery of quadriceps activation and strength post-reconstruction. Patients post ACL-injury will be placed into four treatment groups (NMES and eccentrics; eccentrics only; NMES only, and standard of care) Patients assigned to the NMES and eccentric and the NMES only groups will receive the NMES protocol 2× per week for the first 6 weeks post-reconstruction. MES and eccentric and the eccentrics only groups will receive the eccentric exercise protocol 2× perweek beginning 6 weeks post-reconstruction. Quadriceps activation was assessed via the superimposed burst technique and quantified via the central activation ratio.Quadriceps strength was assessed via maximal voluntary isomeric contractions (Nm/kg). Data will be gathered on three occasions: pre-operative, 12-weeks-post-surgery and at return-to-play.
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