Quadriceps and Hamstring Activation Timing

Quadriceps and Hamstring Activation Timing During Functional Tasks Following ACL Reconstruction

The anterior cruciate ligament (ACL) plays a crucial role in maintaining knee stability and enabling dynamic movement. ACL injuries are common, especially among athletes, and reconstruction surgery is frequently performed to restore knee function. Despite rehabilitation, neuromuscular deficits-particularly in muscle activation timing-may persist. This study will aim to evaluate the activation timing of quadriceps and hamstring muscles during a functional task in individuals who have undergone ACL reconstruction.

This study will be conducted as a cross-sectional, quantitative investigation involving male participants who have undergone ACL reconstruction using semitendinosus and gracilis tendon grafts. Electromyographic (EMG) signals will be collected using the Noraxon Ultium EMG system and analyzed with Noraxon MyoResearch XP software. Muscle activation onset timing will be assessed for the vastus medialis oblique (VMO), vastus lateralis (VL), semimembranosus (SM), semitendinosus (ST), and biceps femoris (BF). Participants will perform a standardized single-leg squat task, during which EMG-based activation timing will be recorded. The findings are expected to provide insight into neuromuscular control strategies and inform rehabilitation approaches following ACL reconstruction.

Inclusion Criteria:

• participants must be males between 18 and 45 years old
• must have undergone ACL repair surgery and be within 6 months to 2 years post-surgery
• should have completed a standard rehabilitation program post-surgery
• must provide written informed consent to participate in the study
• should be in generally good health, without any other significant medical conditions that could affect the study outcomes;
• must have returned to a moderate level of physical activity post-surgery

Exclusion Criteria:

• participants with any neurological disorders affecting lower limb function or any other musculoskeletal disorders or injuries that could affect the lower limb, apart from the ACL injury
• those with cardiovascular conditions that contraindicate participation in physical activity
• those with contraindications to kinesiological electromyography, such as skin conditions or allergies to electrodes
• those who are unable or unwilling to comply with study procedures and follow-ups
• those who have had multiple ACL surgeries on the same knee
• participants involved in ongoing litigation related to their ACL injury