Running does many things to my body. It makes it strong and fit. It has made my lungs more powerful so that I am baffled when people are out of breath having climbed one hill, and I’m not. I loved having my pulse taken and being told it was steady and slow. “That’s an athlete’s pulse.” I wouldn’t call myself an athlete but I won’t stop someone else calling me one. But running has also done and can also do other things: give me blackened and thickened toenails; make me sick; give me the runs. So this Runners World story, oddly headlined “weird science” – there’s nothing weird about it – is illuminating. It explains why I get overtaken by overweight people, with ease; why I need to pee when I’ve already been to the toilet several times; why I felt sick the other night; and why my right knee sometimes sounds like Rice Krispies.