Explosive Neuromuscular Performance of the Quadriceps Muscles Following Anterior Cruciate Ligament Reconstruction: Cross-Sectional Study Protocol

OBJECTIVES: Anterior cruciate ligament (ACL) tears and subsequent reconstruction surgery are associated with a recalcitrant decline in quadriceps muscles’ performance, which can persist for decades, contributing to impaired function, elevated osteoarthritis risk, and poor quality of life. Little is known about why this decline occurs, or if it can be prevented. One important component of quadriceps muscles’ performance that may be impacted by an ACL tear or ACL reconstruction (ACLR) surgery is the ability to rapidly contract and produce force in response to neuromuscular activation, known as explosive neuromuscular performance. This study will compare quadriceps muscles explosive neuromuscular performance and its determinants between injured and uninjured legs of individuals 9–48 months after primary ACLR. DESIGN: Cross-sectional study METHODS: This cross-sectional study will include 48 individuals aged 18–40 years, 9–48 months past a first-time ACLR performed within 12 months of an ACL tear. The primary outcome is isometric knee extension torque (Nm; computerized dynamometry, 90° flexion) at 100 ms after first electrical onset of any quadriceps muscle (electromyography). Secondary outcomes include rate of knee extension torque development (computerized dynamometry), electromechanical delay (electromyography), patellar tendon stiffness (myotonometry), and patellar tendon cross-sectional area (ultrasound imaging). A mixed-effects regression model (95% confidence interval) will assess between-group differences for all outcomes, adjusted for ACL graft harvest site and sex. The association between explosive neuromuscular performance and secondary outcomes will be explored as appropriate. DISCUSSION: Improved understanding of quadriceps muscles explosive neuromuscular performance and its determinants could shed light on mechanisms that underlie the decline in quadriceps muscles’ performance seen after ACL reconstruction and inform treatment targets. JOSPT Methods 2025;1(1):8-16. Epub 25 November 2024. doi:10.2519/josptmethods.2024.0102