Slate has an amazing article on how the brain development of young babies is linked to the amount of playtime they spend on their tummies.
This in itself is quite a startling fact, but it turns out that the campaign to cut cot death – which involved persuading parents to put babies to sleep on their back – has led to a unintentional but general decline in waking ‘tummy time’ and a slowing in movement and nerve development for some babies.
It turns out that this can have surprisingly long-term effects:
How do we know that the babies who miss out on tummy time are at a lasting as opposed to temporary disadvantage? Looking at data from thousands of people born in 1966 in Northern Finland, a research group led by Charlotte Ridgway at the Institute of Metabolic Sciences, Cambridge, has shown that a one-month delay in infant motor development had the same detrimental effect on how a 14-year-old performs in physical education class as a one-unit increase in the same child’s body-mass index. Using the same Northern Finland cohort, Ridgway and her co-authors also mapped a one-to-one link between the age at which infants stand unaided in their first year—another critical prewalking milestone—and their muscle strength and endurance, as well as cardiovascular fitness, at age 31.
It’s a very well researched piece with all the relevant evidence carefully linked in the article, discussing a surprising but important link between brain development and early movement possibilities.
UPDATE: Time has a cautious response to to this article, noting that although the idea is plausible, the data is largely correlational making it difficult to be confident about a lack of tummy time causing developmental delay. Recommended.
Link to ‘Tummy Time: Why babies need more of it than they’re getting’.
Mind Hacks 
This article actually jumps to too many conclusions. Sure, there’s a connection between “tummy time” and motor development, but then the article makes the false connection between tummy time and basically all the other research they cited.
What those studies were really saying was that motor development milestones were found to be important in predicting later physical and cognitive fitness (although the effect sizes were tiny in the cognitive studies). They were *not* studying the effect “tummy time” in any way. In fact, they cannot even show that the variation in motor development milestones was responsible for the adult variation they observed; only that the two were correlated. A common genetic cause of the two could very well be at play.
There are plenty of factors that can affect the timing of motor skill development, both environmental and genetic. I think it’s irresponsible to make the alarmist connection that specifically tummy time-linked motor development variation will *cause* the same sorts of adult outcomes observed in the (wholly unconnected) research that was cited.
Surely the results need to be presented the other way around; spending too much time in laid back positions is not optimal for babies development.
Babies aren’t born physiologically ‘expecting’ to be laid down so much in cots, prams, car seats etc. They’re pretty much an intervention in what would happen naturally.
I’m not at all suggesting that we shouldn’t make use of the advances we’ve made over the years – but it’s the wrong way to look at child development to assume that use of these is the norm and we should measure against them. Shouldn’t we be looking at how a child would develop without them and then trying to find out what constitutes appropriate use of the things that have been invented in relatively recent history and what level becomes over-use and damages development?
Children require shoulder stability to develop control of arms and hands to enable them to skillfully manipulate objects, facilitating exploration of their environment. Spending time on their tummies strengthens shoulders and arms and lengthens muscles used in the hand. It also provides a child with proprioceptive feedback which reinforces their body scheme. It is not surprising that absence or infrequency of time spent lying on their tummy could theoretically have long term consequences.