Here’s A Thought . . .

babywalkingI was just thinking: You know how you are sometimes falling asleep–or are asleep–when your limbs suddenly jerk autonomically (by themselves)? At least, I experience that sometimes, and I assume that you do, too (if you’re attentive).

That limb jerk might have a purpose. Here’s what occurred to me:

When babies are in the womb, they often “kick,” though sometimes the kicks might actually be “punches.” In any event, they move their limbs in a jerky manner that causes their mothers some discomfort (while simultaneously providing delight to the mother, who can feel the child within her, and to others who place their hands on her stomach).

The reason that babies jerk their limbs in this way seems to be that they need to do it: It plays a useful role in their development. By moving their limbs around, the babies are ensuring that their joints work. Our joints–particularly at our shoulders, elbows, hips, and knees–are ball joints that could lock up if the bones grew in the wrong ways. Motion keeps the bones from growing in this way, and if the babies didn’t move in the womb then their bones might grow in ways that would cause their joints to lock up. But by moving them, they make sure that their joints remain fluid and flexible, so that when they emerge from the womb, they can move their arms and legs properly.

So here was my thought: Maybe the limb jerk that we experience when asleep or falling asleep is a survial of the prenatal limb jerk we all have. Maybe it’s a remnant of the reflex that causes our bones to grow right.

If any readers are doctors or others who have info on this, lemme know.

Author: Jimmy Akin

Jimmy was born in Texas, grew up nominally Protestant, but at age 20 experienced a profound conversion to Christ. Planning on becoming a Protestant seminary professor, he started an intensive study of the Bible. But the more he immersed himself in Scripture the more he found to support the Catholic faith, and in 1992 he entered the Catholic Church. His conversion story, "A Triumph and a Tragedy," is published in Surprised by Truth. Besides being an author, Jimmy is the Senior Apologist at Catholic Answers, a contributing editor to Catholic Answers Magazine, and a weekly guest on "Catholic Answers Live."

8 thoughts on “Here’s A Thought . . .”

  1. I’m not a doctor, but I am the mother of five, so I can speak with some authority in this matter 🙂
    You may be right to some extent – a lot of those kicks are little jerky ones. But plenty others have (shall we say) a deliberate feel about them. My second son (now 19) spent the second half of the pregnancy practicing field goals. His older brother was so quiet and still before birth that I began to wonder if he was OK, and I’d thump on my stomach just to get his attention. (He would respond with a short, sharp kick which I took to mean, “Hey, lemme alone!”) The others fell somewhere between on the activity scale, but they all rolled. And rolled. Imagine someone curled up asleep in a bed, who heaves himself over to the other side with a great thump and settles down to sleep again.
    I think even before birth they’re trying out their limbs and seeing what they can do.

  2. As a mom of 2, I can tell you those kicks, while they do delight, are at times are quite painful! I was always under the impression that when we “jerk” at night it was from our muscles relaxing. I have no idea where I may have heard this or if it’s right, but it would be interesting to know for sure what causes it.

  3. As a mom of 2, I can tell you those kicks, while they do delight, are at times are quite painful! I was always under the impression that when we “jerk” at night it was from our muscles relaxing. I have no idea where I may have heard this or if it’s right, but it would be interesting to know for sure what causes it.

  4. Carl Sagan suggests that it may be a leftover instinct from a time when our ancestors had to sleep up in the trees branches. Any limb that begins to throw the sleeping body off balance had to be jerked back quickly (and instinctively), otherwise the Sagan’s ancestor will fall off.
    Ref: Shadows of Forgotten Ancestors

  5. Sleep is in stages. In the deeper stage, the body’s muscles “paralyze” so it won’t be able to act out the dreams. So, the kick is really the result of the body’s switching gears as the muslces begin to be immobilized for preparation for deeper sleep.

  6. The kicks and punches (and especially the headbutts that are so uncomfortable for Mommy) also serve to strengthen those baby muscles, helping to protect life once outside the womb. My baby son was constantly headbutting, hard; and when he was born, he was already able to lift his head. Babies are also born pretty much able to scoot up to their food source. The scooting and head lifting take muscle strength that developed before birth, and help to ensure baby’s survival after birth.

  7. No. 1 Daughter would not so much kick as stretch her legs. I would feel her brace her shoulders down low on the right hand side, then she would extend her legs into the upper left side slowly, rather like someone doing leg-press exercises. Sure enough, after she was born, I could hold her resting against my shoulder with her feet on the palm of my hand and she would continue to do those leg-press exercises. No. 2 Daughter gave short sharp kicks whilst in utero, and lot of ’em, rather than leg presses, and we couldn’t get her to do the same leg-press trick after birth that her older sister did. But she was Queen of the Temper Tantrums, involving a lot of thowing herself on the floor and kicking. I think people’s basic personalities are set long before birth.

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