THE WALL OF PAIN!: It happens to most distance runners and cyclists at some point. You’ve been running or cycling hard, pushing yourself to your limits, when suddenly things take a sharp turn for the worse. Your body feels like it is moving through treacle. Each leg weighs two tonnes. You might even start to hallucinate. Quickly and very unpleasantly, everything seems to be shutting down. You’ve just hit the wall. You may even have experienced or witnessed it at Ironman Wales.

When we run, we burn fat and glucose. The human body has an almost limitless supply of fat cells. But glucose - which the body breaks down from carbohydrates - is different. Our muscles rip through these supplies fairly quickly, generally ‘running out’ after around an hour and a half or two. That is why marathoners and long-distance cyclists “‘arb load’ - to make sure that storage is at capacity - and why they then take mid-race carbohydrate supplements in solid, liquid or gel form.

What happens if you don’t? For some, the system just collapses. Either muscle glucose plummets, leaving the brain yelling at the legs to move. Or blood glucose tanks and the brain becomes a foggy mess. This is the wall. In cycling, the same effect is called bonking. You might still get over that finish line, somehow, but it’s not going to be pleasant.