Do Babies Move Like Us?

True or False?  Babies move just like us

False! From the musculoskeletal perspective, babies have a lot of development to accomplish before they are walking like an adult. 

In fact, children don’t establish their normal gait pattern until they are 7 years old — which means, don’t freak out if your 5-year-old niece is still tiptoeing around the house.  And by the way, tiptoeing is actually a developmental milestone, and if you see a 5-year-old who is not able to tiptoe, then you should worry.

So what exactly does a baby look like when it emerges from the womb?  The cozy intrauterine environment squishes the fetus into a position called physiological flexion. 

In this position, the fetus’s spine is flexed into a “C” shape, while its legs are bent and turned outwards, and its arms are flexed and turned inwards. This has dramatic implications on the newborn’s posture, and explains why infants will lie and sit with their extremities flexed. 

The infant’s hip flexors and lower abdominals are extremely tight from this posture.  Gravity and muscle use are required to pull the neonate’s hips and knees out of flexion, and allow them to gain control of their heads.  By 11-12 months, infants should be able to walk. 

However, despite their quirky posture, newborns demonstrate a curious reflex, called spontaneous stepping. 

When supported on a surface, the infant will kick its legs, as if stepping.  This reflex disappears by two months of age, but can resurface in children with spinal cord injuries.  

Of course, if the gentle parents were to grip their infant less tightly and try the procedure above, the helpless neonate would begin to crumple to the floor. 

This is because walking independently necessitates strong muscle performance, an upright spine with concave and convex curvatures, and valgus knees (a less dramatic version of knock knees).  This combination, as well as a wider pelvis, is responsible for our uniquely bipedal gait.

In an infant, lumbar lordosis (the concave part of the lower spine) develops first and begins increasing by 4 months of age.  Over time, contraction of the infant’s hamstrings and back extensors, when they lie on their stomach, pulls the lower spine out of the C shape. 

By the time they are 4 years old, their lumbar spine is fully concave (lordotic), and they will walk around (albeit somewhat wobbly) at 11-12 months of age.

With the help of the neck extensors, cervical concavity develops slightly after lumbar lordosis.  This is facilitated by the infant lying on its stomach, and lifting its head up to look around. 

Other activities, such as crawling like a bear and playing with their feet while lying down, also help infants progress out of intrauterine physiological flexion.

The other necessary component to walking normally, genu valgum, develops by age 2.  Initially, infants bear their weight (with help in the beginning!) with their knees bowed out like a cowboy. 

Over the next two years, gravity and the weight from their trunks will straighten their legs.  Oddly, they overcompensate and get knock knees until age 8, when their knees return to normal genu valgum, and they indeed walk like little adults.

If you have any questions about muscles and bones, musculoskeletal issues you’ve had or would like to know more about, or anything under the sun related to physical therapy, send them to Ilka.Felsen@ucsf.edu.