Many babies that are born by C-section are what we call 'stuck in flexion'. In other words, they are still slightly curled up in the foetal position (knees to chest) and don't straighten their legs very easily. Traumatic births and position in the womb can also result in muscular or spinal imbalance.
Apart from muscular stiffness, this can contribute to gas build up in the intestinal area and often makes these babies a little harder to burp. A few stretches can make a big difference for babies.
try the brief routine below
they must be relaxed and not cramping, crying, etc
don't force anything!
if they don't seem to like an exercise, move on to the next one and try again later
do them daily to help ease tension and relax your baby