Adaptation of Quadriceps and Hamstring Activation Patterns Following Landing Instruction in Patients with ACL Reconstruction

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With more than 200,000 people undergoing anterior cruciate ligament (ACL) reconstruction (ACLR) of the knee each year, optimal preventive and post-operative rehabilitation strategies are critical not just to individuals working to improve their physical health, but as a public health measure. A growing body of evidence suggests knees which have undergone ACLR exhibit compromised ability to accept weight and attenuate force during high demand activities. This predisposition contributes to relatively poor long-term outcomes for ACLR, including a high risk of re-injury, low rates of return to prior level of function, and significantly increased risk of early onset osteoarthritis (OA). Fortunately, the movement patterns involved in this tendency can be mitigated with instruction and training. Two dominant schools of thought propose divergent training paradigms, however, hampering rehabilitative and preventive effort. One advocates stiffening the joint to protect ligamentous structures by increasing the ratio of hamstring (the muscle that bends the knee) to quadriceps (straightens the knee) activity. The hamstring is thought to protect the ACL; therefore, avoiding a “quadriceps-dominant” movement strategy may decrease injury risk. The other advocates for responsiveness during high-level landing, necessitating a level of compliance in the knee joint and decreased hamstrings to quadriceps activity ratio. Given that most instructional protocols use similar cues to achieve a visually appropriate landing technique, we ask what actually happens during training? Purpose: To explore changes in muscular activity surrounding the knee during instruction for improved knee performance in landing. Methods: Thirty physically active subjects with unilateral ACLR and good clinical results participated in a one-time session analyzing single leg landing of the involved limb off a 20 cm platform using 3-D motion analysis system with force plates. Vertical ground reaction force (VGRF) and peak knee bending served as measures of performance. Vastus lateralis (quadriceps) and biceps femoris (hamstrings) activity were analyzed using surface electromyography (sEMG) and normalized to maximal voluntary isometric contraction (MVIC). Testing was repeated after 5 minutes of instruction in desired landing patterns. Hamstring/quadriceps activity ratios were calculated over the weight acceptance phase of landing, and results were analyzed with paired t-tests. Results: Landing performance improved with training, with increased peak knee bending (mean±SD; pre: 55±11°; post: 78±11°; p