Why does running make me need the toilet?

At the start of every long-distance endurance race the queue for the portaloos stretches round the corner. Any remotely sheltered part of the track is full with participants doing their business in as quick and as dignified a way as they can manage.

Why does it happen?

  • Fluids: not only does the increased volume of fluids drunk before and during an event obviously bring on that call to nature but dehydration through exertion also causes intestinal complaints.
  • Blood flow: as you exercise blood gets diverted to your active muscles and away from your gastro-intestinal tract which can irritate it and cause it to try to flush out irritating substances.
  • Nerves: nerves send us to the toilet at the best of times and the anxiety of knowing that you might need to use the toilet can create a self-fulfilling prophecy, especially when hundreds of people are relieving themselves around you.
  • "Runner's trots": about a third of people experience more severe symptoms believed to be down to the diversion of blood flow and the bouncing up and down motion – it happens less often to cyclists and swimmers.

What can I do about it?

  • Diet: dairy and fatty foods are commonly thought to be culprits, as some runners reduce their fibre intake in the days before an event.
  • Routine: synchronise your training (and pooing) schedule with the timings of your event so your body clock is used to not eating in the two hours before the start and – as our mothers warned us – go to the toilet before it starts. Having a settled routine will also help those nerves. 
  • Other methods: some people find that using an anti-diarrhoea treatment like Loperamide works. Others warn against mixing sports drinks and gels and stick to just one.

If you've got to go, you've got to go

If you're really going the distance, at some point you're just not going to be able to avoid taking a constitutional. The only thing that will help is preparation: mapping potential pit stops along the way and having some toilet paper on you.

You're not alone – it happens to the best of us:

  1. Paula Radcliffe famously won the 2005 London Marathon despite a televised toilet break blamed on grilled salmon.
  2. Ultra-marathon legend Bruce Fordyce keeps a secret weapon in his shorts.
  3. Nadezhda Ilyina's 1997 Los Angeles Marathon win was cruelly disqualified because her gas station toilet break cut 30 metres off the track.