Bodyweight Unloading Effects On Kinematics And Muscle Synergies During Treadmill Training In Cerebral Palsy Individuals

Cerebral Palsy (CP) is a group of brain injury conditions during infancy affecting posture and mobility. Bodyweight support (BWS) treadmill training is an intervention that improves mobility in CP through weight unloading. Gait Deviation Index (GDI) utilizing kinematics and muscle synergies, or groups of muscles recruited and activated as a single unit, have been utilized to discriminate those with and without gait impairments. While assumed, the benefit of unloading and different unloading percentages to improve mobility in CP have not been evaluated. PURPOSE: To examine the effects of two unloading percentages, compared to no unloading, during treadmill walking in age-matched cohorts with CP and typical development (TD) through muscle synergy and GDI analyses. METHODS: Dominant (D) and non-dominant (ND) lower limb kinematics and surface electromyography (EMG) for 8 muscles were recorded in 10 individuals with CP (15+/-3.8 yrs.) and 11 with TD (15+/-3.1 yrs.) at a self-selected speed during 0, 20%, and 40% BWS conditions. EMG data was converted to muscle synergies using non-negative matrix factorization. K-means clustering was used to group synergies across subjects. The number of synergies and GDI were compared across groups and conditions. RESULTS: The CP group had fewer (0%: 5.21+/-0.35; 20%: 4.89+/-0.37; 40%: 4.86+/- 0.23) but not significantly (p = 0.61) mean synergy number than TD (0%: 5.15+/-0.56; 20%: 5.05 +/-0.54; 40%: 4.92 +/- 0.24) with inconsistent change across conditions. With increasing BWS, 21.9% of synergies showed changes in TD and 11.5% in CP with most reflecting reduced activation in Tibialis Anterior and Extensor Hallucis Longus muscles during weight acceptance. GDI showed a triple interaction (p = 0.045) with worsening (reduction) on both limbs from 0 to 20% BWS in TD (D: -3.91+/-7.84, ND: -2.52 +/- 8.1), and improvement in CP on the dominant side (D: +4.81+/-8.36). Improved GDI with BWS correlated with higher synergy numbers in CP. CONCLUSION: The number of synergies deployed during walking was not sensitive enough to differentiate groups or conditions or determine the optimum unloading percentage. BWS had greater effects on muscle synergy changes in the TD group, indicating poorer modulation in the CP group to meet increasing BWS demands. GDI best differentiated group effects with BWS.