Person running on sunny dayNot only are we going into our third heatwave of the year, but UK heatwaves are notoriously worse than in other countries, and experts tell HuffPost UK that we can expect many more in the future. All grim stuff. But after sweating my way through a 5k that left me lobster-red recently, I was left with a slightly more self-interested question: how hot is too hot to run? Previously, coaches told us when a chill should keep you indoors (“Runners should carefully consider their training plans for temperatures between 0°C and -10°C,” running coach