Women with patellofemoral pain show altered motor coordination during lateral step down

Patients with patellofemoral pain (PFP) present altered activation of the hip and knee muscles. Electromyography (EMG) analyses in PFP patients are usually performed individually for each muscle. However, several studies suggest that the central nervous system may modulate neural commands directed to groups of co-activated muscles, called muscle synergies. Investigating the synergistic organization in PFP will advance our knowledge of the influence of pain on muscle coordination. This study aimed to compare the motor coordination between women with and without PFP during the lateral step down (LSD). 15 women with PFP and 14 asymptomatic women underwent three-dimensional kinematics and EMG assessment during LSD. The Movement Deviation Profile (MDP) was calculated from kinematic data. Muscle synergies were extracted from EMG data of eight lower limb muscles using a non-negative factorization algorithm. Results revealed differences in MDP and an altered synergistic control between women with PFP and asymptomatic while performing the same motor gesture. Particularly, the variability accounted for (VAF) when using 3 synergies to reconstruct EMGs of the PFP group was higher than in the control group, suggesting reduced complexity of motor control in PFP. Detailed synergy analyses highlighted specific differences between groups in vastii and rectus femoris, which are muscles with a crucial role during the squat phase and the transition to rise phase of the LSD. This study shows the ability of muscle synergies analysis to reveal impaired motor coordination in PFP patients, and has the potential to be explored as a complementary tool to current clinical assessment techniques.