Why Tummy Time?

A young baby I’m acquainted with has been sleeping on his back (the supine position), as recommended, for the last two months. His parents have been busy with a list of things you can well imagine, and had not been doing any “tummy time” with him. Now he has a little flattening of the back of his head, and his pediatrician has started to urge “tummy time”--- putting him in the prone position (on tummy, not back) while he’s awake and ready to play a bit.

What’s the purpose of this? Is it all about keeping a nice round head?

It’s true that people in industrialized countries (as well as many others) don’t like a person’s head to be flattened in back. Some cultures have liked skull shapes that we would think strange, and put babies on cradleboards or bound their heads in other ways so they would grow into high-fashion shapes. Babies’ skulls are not yet completely hardened and bony, nor are the skull bones fused into a solid dome—that’s why there’s still a “soft spot” on top of the head. Because the individual bones are still somewhat soft, and because not all the skull plates are connected, it’s easy for continuing pressure on one spot to change the shape of the skull. Lying in one position all the time may deform the skull, and it’s a lot easier to prevent this deformation than to cure it.

But---  there’s a lot more to the issue than having a nice head. Babies’ muscular, bone, and motor development is affected by the movements they get to make. This seems surprising, I know, because we usually think of the baby’s development as just unfolding bit by bit, physical growth and movement control emerging according to a genetic timetable as long as the baby is well fed and cared for.

Young babies (let’s say, birth to three months) can make some movements when lying on their backs. They can kick, wave their hands, and so on--  although for the first month or so they’re “prisoners” of their own reflexes, and their movement of one arm forces the other arm and the head to go into new positions. They can’t lift their heads, though. The head is very heavy compared to the rest of the baby, and even adults find that to lift the head in the supine position (back-lying) is much harder than to lift it when prone. Remember, too, that young babies are likely to lie with the legs somewhat drawn up rather than extended, and this makes it even harder for the weight of the body to counterbalance that big head.

When in tummy position, babies can work toward a lot of new skills that are too difficult in the supine position. Even a newborn can usually lift the head enough when in prone to be able to turn the head from side to side, which is difficult for the back-lying baby. Lifting and moving the head in that way fosters the development of the neck muscles and helps steady the head in all sorts of positions--  which, by the way, helps the baby move the head to look at interesting things and get more involved with the world around him.

Once the head is being lifted a bit, it’s easier for the hands to come forward and provide a steadying base for the baby in tummy position. This works the arm and shoulder muscles, and enables the baby to move toward pushing on the supporting surface and bit by bit getting not only the head but the chest up--  essential steps toward crawling, but also important for getting a good look at the world. Incidentally, while pushing up, the baby works on opening up and flattening out the hands that were clenched fists most of the time in earlier weeks. The increased arm and shoulder strength, and the development of the chest muscles, also contribute to being able to sit on someone’s lap with a little support of the hips, and to join in the social whirl. Sitting up makes it easier to reach, also to see people’s faces and learn about them--  and so on and on.

Would it be a big problem if the baby didn’t get tummy time? The possible flattening of the head is certainly undesirable, but everything else would probably develop after a while. Even a back-lying baby eventually learns to turn over into the prone position and goes on from there, but with motor skills emerging later or in a different order than what you might think.

Here’s one of the issues to keep in mind: most “baby books” and lists of motor milestones tell you what babies did many years ago. Until perhaps ten years ago, parents in the United States had been advised for decades to keep their babies on their tummies. As a result, the babies developed head and chest control and other abilities earlier than back-lying babies do. “What the book says” may be somewhat different from what today’s back-lying baby does. “Tummy time” is designed to give the babies the health and safety advantages claimed for back-lying as well as the types of motor development the prone position encourages, and the cognitive development that goes along with them.

A baby who has been lying on his back for a couple of months will probably not be best pleased when placed in the prone position. Lifting that big head may be frustrating and difficult, and he’s not used to it. The most helpful thing a parent can do is to put is to put his or her face where the prone baby can see it with a little effort. The social support of a smiling, attentive face helps the baby organize this new activity. If the baby is on the floor, it may be hard to put your face in the right place without dislocating your neck, so try a tabletop with a blanket on it, and sit right beside it. (Naturally, you’re not going to step away for even a minute and leave the baby there!) If you have an old-fashioned crib whose side lets down, that makes an even better arrangement.

One other hint: if you place a hand lightly on the baby’s bottom, you help him counterbalance the heavy head so it’s easier to lift. When he succeeds, it’s so exciting that he’s likely to work even harder and can soon manage without your help.

There’s no real need to rush development along, and I don’t mean to suggest that your child is in some kind of race or won’t get into Harvard if you haven’t done plenty of tummy time. But as motor and cognitive skills move along, babies and parents have more to do together and have more fun, and that always helps when young families are navigating this complicated part of life.