Effect Of Supraspinal Input On Muscle Activation During Assisted Leg Cycling After Complete Spinal Cord Injury

Following a motor complete spinal cord injury (SCI), the loss of descending pathways in the central nervous system directly affects voluntary motor control below the level of injury. Previous studies have shown supraspinal centers are important for postural control and step initiation during locomotion. PURPOSE: The purpose of this study was to determine the relationship between supraspinal input conditions (intentional and non-intentional) on muscle activation in individuals with motor complete SCI. METHODS: Eight individuals with chronic, motor complete SCI participated in the study. Using a leg cycling model to limit postural demands, the participants sat in their wheelchair with their feet secured to the pedals of a cycle ergometer while two experimenters rotated the cranks. Participants first intentionally focused on activating their muscles (Intent; No Math) for approximately 10 revolutions, and then answered simple math problems (No Intent; Math) for 10 revolutions. Surface electromyographic (EMG) was recorded bilaterally from the Vastus Medialis and Vastus Lateralis (VAS, N = 32), Rectus Femoris (RF, N = 16), Biceps Femoris (HAM, N = 16), Gastrocnemius Medialis and Gastrocnemius Lateralis (GAS, N = 32), Soleus (SOL, N = 16), and Tibialis Anterior (TA, N = 16). A chi-square test of independence was performed using categorical variables with the EMG activity that coincided with pedaling frequency (EMG Entrainment) for each muscle on both sides of the body during Math and No Math conditions. RESULTS: EMG entrainment during leg cycling was observed in VAS (N = 13/32), RF (RF N = 4/16), HAM (N = 7/16), TA (N = 2/16), SOL (N = 4/16), and GAS (N = 10/32) during the Math condition. During the No Math condition, EMG entrainment was observed in VAS (N = 11/32), RF (N = 3/16), HAM (N = 10/16), TA (N = 3/16), SOL (N = 7/16), and GAS (N = 13/32). When comparing each side of the body there was a significant relationship in EMG entertainment for the intent (No Math) condition at the right Soleus muscle only, (N = 5), p < .05, but not the left, (N = 2), p = .59. CONCLUSIONS: Supraspinal intent was more likely to be associated with muscle activation entrainment, compared to no supraspinal intent, in the right soleus. Further investigation is warranted to determine if any supraspinal input on muscle activation remains after motor complete SCI.