A major complication after cruciate ligament injury and surgery is arthrogenic muscle inhibition of the quadriceps, which is characterised by a deficit in voluntary muscle activation in the affected leg. This can hinder rehabilitation processes, lead to impaired knee function, and negatively impact the patients' quality of life. The primary objective of this study is to assess whether voluntary quadriceps activation on the injured side is facilitated by the concomitant application of neuromuscular electrical stimulation (NMES) on the contralateral quadriceps.

The primary objective of this study is to assess whether injured-side voluntary quadriceps activation before and after ACL surgery is facilitated by the concomitant application of NMES on the contralateral quadriceps (uninjured side), in comparison to a control (CTRL) condition that does not involve any contralateral activity (passive rest) and to a voluntary (VOL) condition that involves a maximal voluntary contraction of the contralateral quadriceps.

Inclusion Criteria:

• Patients undergoing ACL surgery with semitendinosus tendon autograft in the Schulthess Clinic
• Unilateral and primary ACL injury (with/without diagnoses of additional meniscus injury)

Exclusion Criteria:

• Previous surgery/ligament rupture in injured or uninjured knee or hip
• Severe pain in the uninjured-side quadriceps or knee joint
• Ongoing pregnancy
• BMI >30 kg/m²
• Neuromuscular disease
• Open wounds or tissue injuries on the anterior aspect of the thigh
• Additional rupture of other knee ligaments (posterior cruciate ligament, medial collateral ligament, lateral collateral ligament)
• Implanted metallic/electronic devices (cardiac pacemakers, defibrillators)
• Patients getting a femoralis block (peripheral nerve block) after surgery will be excluded for the post-surgical appointment
• Insufficient language comprehension