Lactate threshold training has become rather fashionable in recent years due to, in part, the success of several Norwegians across running and triathlon. Athletes, including Jakob Ingebritsen and Gustav Iden, have achieved success from intensity control using lactate measurements in training. Lactate is a commonly misunderstood substance in the body. Conventional wisdom dictates that lactate is bad — something that ‘builds up’ when you go hard — so ‘fitter’ athletes produce less and, therefore, can go at some given intensity for longer. But this is an oversimplified interpretation of what’s happening. Lactate isn’t the waste product, as once believed.