The Limited Range of Motion of the Knee Does Not Fully Explain the Altered Neural Control of Plantar Flexors During Gait in Non-Neurological Knee Flexion Contracture

Knee flexion contracture (KFC) may occur in the late stages of arthropathies, including osteoarthritis and haemophilic arthropathy. The impact of KFC on neuromuscular control remains unclear, particularly for the affected ankle plantar flexors. Surface electromyography (EMG) is widely used to assess muscle activation patterns, whereas intermuscular (EMG-EMG) coherence provides insight into common neural input. In this study we compared the neural control of ankle plantar flexors during gait between individuals with haemophilia and KFC (chronic; n = 8), and healthy individuals without (control; n = 15) and with an artificial constraint (artificial; n = 15). Bipolar EMG from plantar flexors was recorded during 30-m overground walking (1 m/s). Intermuscular coherence was estimated at 8-60 Hz during the stance phase and significance was determined using a permutation method. The chronic group showed greater knee flexion than controls (24-29 deg vs 2-20 deg), higher EMG amplitude at foot contact, and increased intermuscular coherence in the alpha (8-12 Hz) and beta (12-30 Hz) bands at mid-stance. Despite comparable sagittal knee kinematics between constrained conditions (chronic: 24-29 deg; artificial: 20-32 deg), early-stance EMG amplitude and mid-stance beta-band intermuscular coherence were higher in the chronic group across plantar-flexor pairs. Increased plantar-flexor activation in the chronic group suggests higher neural drive, while higher intermuscular coherence reflects greater common input to the plantar flexors. These findings indicate that limited ROM alone does not explain the altered neural control of plantar flexors, suggesting neural adaptations associated with non-neurological chronic KFC.