On long trails, carbs and fluid decide it: aim for around 90 g/h from 3 hours, drink to thirst with salt, train your gut and feed your recovery.
On long trail runs, carbohydrates and fluid decide your performance — and your gut has to learn to tolerate both. The honest rule of thumb: from three hours of effort you aim for around 90 g of carbs per hour; for beginners 30–50 g/h is enough; well-trained, up to 120 g/h is possible and even limits your muscle damage. You drink to thirst, with salt — not ahead, because over-hydration is a real risk. The biggest problem is rarely the head, it's the stomach: 65 to 82 % of ultra trail runners battle gastrointestinal issues. The good news: tolerance is trainable. In this guide you build a fueling and recovery strategy that you test in training before it counts in a race.
It depends on duration. Up to about two hours, 30–50 g/h is enough. From three hours the need rises to about 90 g/h, ideally in a 2:1 glucose-to-fructose ratio, because your body absorbs two sugar types in parallel. Those who've trained their gut tolerate up to 120 g/h in competition — and that even measurably protects against muscle fatigue. Ramp up slowly from the bottom rather than jumping straight to the maximum.
With gut training and a few rules. Practice your race fueling over weeks on long runs so your gut adapts — tolerance is trainable, not just a matter of dose. Keep drinks under about 8 % concentration, vary flavors against flavor fatigue and drink enough (roughly 0.4–0.8 L/h aids absorption). Fast pace, heat and dehydration clearly worsen symptoms.
To thirst, not ahead. Plan roughly 450–750 ml per hour and add sodium — around 500–700 mg per liter, more in heat. Too much fluid without salt dilutes your blood and can trigger a dangerous hyponatremia that affects up to half of ultra finishers. Your thirst and a rough weight check before and after long runs are your best compass.
In the first one to two hours after a hard run, carbs plus some protein are most effective for rebuilding glycogen and muscle. Drink to replace losses and salt your food a little more freely. After very long runs your muscle is objectively weakened and needs building blocks — recovery begins at the buffet, not in bed.
Besides refueling, sleep, moderate movement and patience count. After hard downhill or ultra runs, muscle damage markers are elevated for 48–72 hours and strength is really reduced. Plan easy days afterward, eat enough protein spread across the day, and don't expect peak form right away. Feed your recovery and you're ready sooner for the next hard stimulus.
Over-hydration can become life-threatening: drink to thirst and replace sodium in prolonged heat instead of forcing water into yourself. Test every new fuel in training first — a race is the wrong place for experiments. And respect recovery: the strength loss after hard runs is measurably real; going full-gas again too soon risks overuse and injury.
On long runs, run a simple "fuel timer": set a discreet alarm on your watch every 20–30 minutes to remind you to eat and drink. Under fatigue almost everyone forgets to refuel, and an empty tank hits back abruptly an hour later (practice, backed by). Regular small amounts beat rare big portions — for both the stomach and performance.
From three hours of effort, around 90 g/h, ideally in a 2:1 glucose-to-fructose ratio; for beginners 30–50 g/h is enough. Well-trained, up to 120 g/h is possible, and this high intake even measurably limits your muscle fatigue. Ramp up slowly and practice it in training.
With gut training: practice your fueling over weeks so the gut adapts — tolerance is trainable. Keep drinks under about 8 % concentration, vary flavors and drink enough. Pace, heat and dehydration worsen symptoms, which 65–82 % of ultra runners know.
To thirst, around 450–750 ml per hour, with about 500–700 mg of sodium per liter, more in heat. Don't drink ahead: too much fluid without salt can trigger a dangerous hyponatremia that affects up to half of ultra finishers. Thirst and weight checks are your compass.
Refuel with carbs plus some protein in the first one to two hours, replace fluid and salt, and plan easy days. Muscle damage markers stay elevated for 48–72 hours and strength is really reduced. Sleep, enough protein and patience bring you back fastest.
Trailrunning: Strategy and Tactics