pregnancy tummy and calendar

Everyone seems to have a story about a friend who had a baby then suddenly started running PBs. But is getting faster after pregnancy really the norm?

I was running with a friend the other day when he turned to me, looking a little awkward, and began to ask, ‘Is it true that runners who’ve had babies…’

‘I know what you’re about to ask,’ I butted in. ‘And the answer is, I don’t know.’

Whether women get fitter after having a baby is a question everyone seems to be asking at the moment. From Julia Radcliffe’s post-baby marathons, to Serena Williams winning the Australian Open while eight weeks’ pregnant, we can all point to someone for whom pregnancy was like some kind of miracle baby juice. Almost ‘free’ fitness.

Maybe it’s to do with red blood cells. Maybe it’s heart size, hormones or an expanded rib cage. Maybe it’s the sheer relief of no longer being pregnant… there are lots of theories why some women seem to get faster after pregnancy.

And, not surprisingly, they’re mostly still just that: theories.

As Dr James Pivarnik, professor of kinesiology and epidemiology at Michigan State University, told Runner’s World in 2016, it would be tricky to get funding for definitive research.

But here are a few of the main ideas about how having a baby might make you faster. Have a read before you jump off the pill.

Pregnancy and red blood cells

During pregnancy, blood volume increases by up to 50 per cent. Red blood cells increase too (although anyone who’s had pregnancy-related anaemia will know they don’t always increase fast enough). Compared with non-exercising mothers, women who exercise during pregnancy have even more blood and even more red blood cells, one study has found.

Some people have suggested this helps women run faster after having a baby. After all, the aim of altitude training is to increase red blood cells, right?

Maybe. But as the study’s author Dr James Pivarnik has told Pregnancy & Baby, any boost is probably short-lived. “Most of the women I’ve worked with are relatively back to normal within 16 weeks,” he said.

Pregnancy and heart size

From about week five of pregnancy, your heart changes. Its capacity increases, allowing it to pump out more blood with each stroke. It also pumps faster. The intent is a happy fetus with all the oxygen it needs.

But could it also help new mummies run faster once baby is born?

This makes logical sense: more oxygen-rich blood to your muscles is of course good for performance. The catch is, no one can say when changes disappear. According to one study of 30 women, they gradually return to normal and are still partly there a year after birth (which is when the study ended).

Pregnancy and VO2 max

If you’re a training geek, you’re probably wondering what these mean for your VO2 max.

VO2 max is, essentially, the maximum amount of oxygen your body can take from the air and deliver to your muscles via your lungs. A higher VO2 max is a sign of higher aerobic fitness.

Again, there are a couple of studies on pregnancy and VO2 max.

One 1991 paper published by Medicine & Science in Sports and Exercise measured the VO2 max of 40 women, 20 of whom subsequently became pregnant and continued training at a reduced level. Around nine months after the babies were born, the researchers measured a small but significant increase in VO2 max among the women who’d had a baby. This suggests your aerobic fitness might get a boost if you feel able to keep up some training during pregnancy.

But then, fewer than a third of recreational runners do run in the last trimester. So then what? A study published by the same journal 14 years later tested the VO2 max of 63 women before and after pregnancy. This time, their training levels weren’t specified. Six weeks after delivery their VO2 max was on average lower – possibly due to reduced training – and was still lower months later.

Biomechanical and muscle changes

It’s been speculated that carrying around extra pregnancy weight may also boost women’s performance once that weight is gone. Makes sense – although many of us know it doesn’t always go away again! And a statement in The British Journal of Sports Medicine on exercise in pregnancy in 2017 stated that not enough is known about this factor.

Brain theories

Many news stories about why some new mums get faster end up on ‘increased pain tolerance’, ‘more focused training’, ‘being happier’ or ‘the relief of being away from your kids’. This blog post is no different!

While it makes sense that pregnancy could have some lasting changes – including making you faster – they’re far from proven.

On the other hand, lots of things about having children aren’t good for your running: eg pelvic pain, pelvic floor dysfunction and diastasis recti. These are things that don’t make headlines.

So if my friend was to ask me again, I’d say sure, it’s possible that pregnancy gives you a fitness boost.

Just don’t call it free.

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