Quadriceps Function After Exercise in Patients with Anterior Cruciate Ligament-Reconstructed Knees Wearing Knee Braces (Original Research) (Clinical Report‪)‬

Quadriceps muscle weakness and central activation failure (1) are common after anterior cruciate ligament (ACL) injury and reconstruction (ACLR). (2,3) The phenomenon of persistent weakness and activation failure may be explained by arthrogenic muscle inhibition, a reflex response to joint injury that may be magnified after aerobic exercise (4) in which a muscle cannot contract to its full potential. (2,3) Persistent quadriceps weakness after knee joint injury is a likely cause of altered gait patterns (5) and shock attenuation capabilities during dynamic activities. (6) Identifying potential sources of arthrogenic muscle inhibition and therapies to help overcome inhibition is paramount to preventing excessive muscle weakness and altered lower extremity biomechanics after joint injury. Conventionally, a variety of knee braces have been prescribed to assist people with ACLRs maintain joint stability and prevent further joint injury during exercise. (7,8) Rigid braces and neoprene sleeves are often worn during athletic activity (9-11) for a variety of reasons; however, little is known about how braces and sleeves influence neuromuscular adaptations during exercise. Quadriceps muscle function has been shown to deteriorate after a standardized treadmill aerobic exercise protocol. (12) This finding is clinically important because knee braces or sleeves are often worn after ACLR during athletic activities, yet whether such braces help or hinder neuromuscular function of the quadriceps, which is known to be deficient after ACL injury and ACLR, is unknown. (13) Although decreases in muscle activation may occur during aerobic exercise, clinicians should be aware of the influence of external knee joint bracing on quadriceps function in people with ACLRs during prolonged exercise. The purposes of our study were to compare (1) the quadriceps muscle central activation ratio (CAR) and normalized torque measured during a maximal voluntary isometric contraction ([T.sub.MVIC]) immediately after the application of a rigid knee brace or neoprene sleeve and (2) changes in CAR and [T.sub.MVIC] after aerobic exercise in people with ACLRs wearing a knee brace or neoprene sleeve while exercising.