Infant legs upward may be a physiological phenomenon, but also may be pathological, mainly based on the age to identify. In general, 4-8 months old infants legs upward is a normal phenomenon, because this age body in the second flexion period, leg strength is generally greater, will occur leg upward phenomenon. If there are other abnormal movements, parents do not have to worry too much, these are signs of increased muscle tone. As the age increases, the phenomenon of leg cocking will gradually decrease and disappear. If after 10 months of age there is still always leg up, consider whether it is a pathological phenomenon, such as cerebral hypoxia, soft tissue injury, hip dislocation, etc. There are many pathological reasons that can cause legs to buckle, all of which can affect the normal development of the infant, so it is important to seek treatment at the hospital when abnormalities are found.