When you bend one of your baby’s legs towards their belly while they are lying on their back, the baby will respond by extending the other leg. The presence of this reflex indicates the newborn can maintain equilibrium (balance) through the appropriate functioning of the brain’s cerebellum and cerebral cortex. This reflex is associated with the coordination of leg muscles required during walking, through alternate leg muscle contractions.
Testing the Crossed Extensor Reflex
To test this reflex, gently bend one of your baby’s legs towards the belly while they lay on their back and watch as your baby extends the other leg. This occurs in order to maintain balance as one leg compensates for loss of support when the other leg is bent towards the belly. This reflex involves muscles of the hip and abdomen that also contract to shift the body’s center of gravity.
This newborn reflex (primitive reflex) usually remains present until four to six weeks of age.
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