How many grams of carbohydrate you take in per hour. Over middle and long distance 60–90 g is the target — from a single sugar source only about 60 g is usable.
Once a race runs for several hours it's the rate that decides, not the total. The mechanism explains the 60-gram ceiling: your gut can only process a single carbohydrate source such as pure glucose up to roughly 60 grams an hour. Mix glucose and fructose and two separate absorption routes run at once — two checkouts instead of one — and the rate rises noticeably. The classic mistake is waiting for hunger: start within the first 15 to 20 minutes on the bike — a deficit an hour in is almost impossible to claw back. And never test a new gel on race day; gastrointestinal trouble is the most common complaint in triathlon, and in one study 59 percent of long-distance athletes reported it. What gets missed: carbohydrate alone isn't enough. Every litre of sweat costs you 400 to 1,500 milligrams of sodium — drink only water for hours and you risk dilutional hyponatraemia.