Muscle activity during different stepping modes in decerebrate cat

The basement of the vertebrate motor system is flexor reflex whilst the extensor thrust supposed to be an optional factor for the stepping. But different forms of stepping (in opposite directions) could be differently depending upon it, since the sensory input is crucial for the stepping. The most investigated is forward stepping (FW) being the most “learned” in both phylogeny and ontogeny. In opposite, the backward (BW) stepping is associated with mostly the specific forms of behavioral activity. We compared an EMG activity of several hindlimb muscles moved the hip (iliopsoas, IP, sartorius (SR), adductor magnus (AM), biceps femoris posterior (BFP)), knee (rectus femoris (RF), vastus medialis (VM)), and ankle (tibialis anterior (TA), gastrocnemius medialis (GM), soleus (SL)) joints, in decerebrate cats stepped under epidural electrical stimulation. For most cats, an activity of hip flexors (IP, SR) was lower, hip extensors (AM, BFP) – higher, knee extensors (RF and VM) – lower, ankle flexor (TA) – lower, ankle extensor (GM) – higher for BW stepping than for FW stepping. For all muscles but SR (with minimal sample size) differences were statistically significant (Wilcoxon test). Only in SL, no clear predominance for any stepping mode was obtained. These data point out to different balance in flexion and extension during stepping in opposite directions.