Context: Activation time of the quadriceps is important in determining injury risk in professional soccer players.
Objective: To compare the activation time of the quadriceps and hamstrings muscles during a movement that puts stress on anterior cruciate ligament (ACL) to assess the risk of ACL injury.
Design: Case series.
Setting: University laboratory for movement analysis.
Patients or other participants: Twenty (10 males and 10 females) professional soccer players.
Intervention(s): An inertial sensor and 4 electrodes positioned on the quadriceps and hamstrings muscles were used for the surface electromyography. The athlete resting on 1 leg dropped, from a 32-cm-high platform, on the suspended foot (testing leg), without jumping or lowering his center of gravity and maintaining single-leg landing for 5 seconds. Using a software, it is possible to calculate the activation time of the rectus femoris, vastus medialis (VM), biceps femoris, and semimembranosus muscles before ground contact.
Main outcome measures: To evaluate the activation times of the rectus femoris, VM, biceps femoris, and semitendinosus muscles before ground contact in comparison with the range of normality calculated by the manufacturer.
Results: All male soccer players demonstrated a low risk related to the correct activation of all the examined muscles, while female soccer players demonstrated delayed activation of the VM.
Conclusions: Delayed activation of the VM registered in females determines an increase in anterior shear force, which is an important risk factor for incurring an ACL injury. This testing protocol becomes adequate for the screening of high-risk athletes and for targeting interventions to specific imbalances that may increase injury risk.
Keywords: electromyography; female athletes; football; kinematics; quadriceps.