Contribution of Neuromuscular Factors to Quadriceps Asymmetry After Anterior Cruciate Ligament Reconstruction

Abstract

Context: To quantify quadriceps weakness after anterior cruciate ligament reconstruction (ACLR), researchers have often analyzed only peak torque. However, analyzing other characteristics of the waveform, such as the rate of torque development (RTD), time to peak torque (TTP), and central activation ratio (CAR), can lend insight into the underlying neuromuscular factors that regulate torque development.Objective: To determine if interlimb neuromuscular asymmetry was present in patients with ACLR at the time of clearance to return to activity.Design: Cross-sectional study. Conclusions: Interlimb asymmetries at return to activity after ACLR appeared to be regulated by several underlying neuromuscular factors. We theorize that interlimb asymmetries in isometric and isokinetic quadriceps strength were associated with changes in muscle architecture. Reduced CAR, TTP, and RTD were also present, indicating a loss of motor-unit recruitment or decrease in firing rate.

Contractile rate of force development after anterior cruciate ligament reconstruction—a comprehensive review and meta‐analysis

“…56,58,65,71,72 Comparisons between participants with and without ACLR were pooled from four studies (n = 211 participants). 47,66,69,73 As the main study finding, ACLR resulted in substantial between-limb asymmetry (ie, ACLR limb deficits) in RFD, evidenced by moderate-to-large (>0.7) SMDs in early-and late-phase RFD for both the knee extensors and flexors. Large (>1.0) SMDs were also observed when comparing individuals with ACLR to uninjured controls for early-and late-phase RFD for both the knee extensors and flexors.…”

“…Bone-patellar tendon-bone (BPTB) autografts were mostly used for ACLR in the present analysis. 56,58,59,[65][66][67][68][71][72][73] This may explain the more marked and persistent between-limb asymmetry in knee extensor RFD compared to knee flexor RFD. 9,71 In support of this notion, between-limb asymmetry deficits based on MVC also have been observed for the knee extensors in individuals with BPTB autograft.…”

“…14,20 In terms of knee flexor (hamstring muscle) function, while the biceps femoris muscle may contribute to RFD strength assessments at 15-30° of knee flexion, 77,78 the semitendinosus and gracilis muscles are strong agonists for knee flexion torque beyond 75° of knee flexion. 58,73 As the semitendinosus autograft is a common ACLR technique, this highlights the importance of considering the torque-joint angle relationship when assessing RFD capacity. Jordan et al 58 study was the only study to assess knee flexion at larger angles (70°).…”

“…Rehabilitation protocols were informed briefly and not summarized in fine detail in the studies included in the present analysis. 56,58,59,[65][66][67][68][71][72][73] It is possible, therefore, that insufficient rehabilitation efforts are at least partially responsible for the persistent RFD between-limb asymmetries observed after ACLR. Maximal and explosive-type (ie, performed with high RFD) resistance training 41,107,115 including ballistic training (ie, the use of a relatively light external load with maximal intentional velocity), ensuring maximal intent to generate rapid force, and sufficient similarity between training and testing movement patterns are all factors known to enhance RFD.…”

Muscle activity in asymmetric bench press among resistance-trained individuals

“…In rehabilitation from serious long-lasting injuries with immobility (i.e., anterior cruciate ligament ruptures or shoulder dislocation), the strength relationship between limbs is one way of measuring the progression of a rehabilitation process (Norte et al 2020 ; Johnson et al 2018 ). However, unequal strength between limbs may increase injury rate and reduce performance in activities or sports where symmetry in strength between limbs may be crucial (i.e., alpine skiing, sprinting) (Maloney 2019 ).…”