Effect of Surface EMG Biofeedback on Quadriceps Inhibition Release During Postoperative Knee Rehabilitation

Arthrogenic muscle inhibition (AMI) is a reflexive neurological response commonly observed after knee surgery. It results from altered afferent input originating from the injured joint, leading to reduced voluntary activation of the quadriceps muscle. AMI contributes to muscle weakness, impaired knee extension, gait abnormalities, and delayed functional recovery. Persistent inhibition may negatively affect long-term rehabilitation outcomes.

Surface electromyography (sEMG) biofeedback provides real-time visual information about muscle activation, enabling patients to voluntarily adjust their contractions during rehabilitation exercises. Previous studies suggest that EMG biofeedback may improve neuromuscular activation and motor learning, although evidence remains limited.

The BIOQUAD study is a prospective, within-subject Single-Case Experimental Design (SCED) conducted in adult patients undergoing rehabilitation after knee surgery who present AMI. This design was selected because of the high inter-individual variability in neuromuscular recovery and the exploratory nature of the study. Each participant acts as his or her own control through repeated measurements under two experimental conditions.

Each participant will complete eight standardized rehabilitation sessions over approximately three weeks:

• Four sessions with visual sEMG biofeedback.
• Four sessions without visual feedback while EMG signals are still recorded.
• The order of conditions will be randomized using a predefined balanced sequence to reduce learning and order effects.

At the beginning of each session, maximal quadriceps activation (EMGmax) will be calibrated using three maximal voluntary contractions. Participants will then perform six standardized contractions targeting 80% of EMGmax, each maintained for five seconds and separated by fifteen seconds of rest.

The primary endpoint is contraction accuracy, defined as the percentage deviation from the target muscle activation level. Secondary outcomes include:

time spent within the target activation zone (±5%);

• motor latency;
• maximal EMG activity (EMGmax);
• motor engagement score;
• perceived exertion (Borg scale);
• pain intensity (Numeric Rating Scale). Data will be analyzed using SCED methodology with visual and descriptive analyses focusing on level, trend, variability, and overlap between experimental conditions. Results will primarily be interpreted at the individual participant level before descriptive synthesis across participants.

Inclusion criteria

• AMI following knee surgery, as classified by the Santi classification system
• Aged 18 or older
• Enrolled in or covered by a social security program
• Able to understand instructions and participate in standardized rehabilitation sessions

Exclusion criteria

• Acute pain.
• Neurological condition.
• Skin lesion at the electrode site.
• Allergy to the electrode.
• Under legal protective measures such as guardianship or court-ordered protection