For any effort longer than about 90 minutes, how full your glycogen tank is at the start is one of the biggest predictors of how you'll finish. In the days before a big event, endurance athletes progressively raise their daily carbohydrate — often into the range of 7–12 g per kilogram of body weight per day — to load the muscles and liver.

Closer in, the pre-effort meal does the fine-tuning. In the 1 to 4 hours before a long session, eat roughly 1–4 g of carbohydrate per kilogram of body weight, keeping it lower in fat and fibre so it digests cleanly and doesn't sit heavy. A glucose–fructose blend is ideal — it tops up liver glycogen, the reserve that keeps your blood sugar steady early on. And start hydrated: fluid and a little sodium on board beats trying to catch up once you're already behind.

There's a moment in every long effort where the tank runs low and the legs go heavy — the wall. Feed your body a steady stream of carbohydrate and you push that moment back, often out of the picture. How much you need scales with how long you're out there:

Under an hour: stored glycogen is usually enough — water and electrolytes will carry you.
One to two-and-a-half hours: aim for 30–60 g of carbohydrate per hour.
Beyond ~90 minutes and into the long stuff: climb toward 60–90 g per hour.

At the higher end, one detail changes everything. Your gut absorbs glucose through a single transporter that saturates near 60 g per hour — pile on more glucose alone and it just sits there. Add fructose, which crosses the gut wall by a different route, and you unlock more usable fuel: a roughly 2:1 glucose-to-fructose blend can lift the carbohydrate your body actually burns by about 50% versus glucose alone. That's why the best fuels are a deliberate blend, not pure sugar.

In practice, 60–90 g/hour is about two to three energy gels an hour, or one gel plus a bottle of Sport Drink Mix. Two habits make it stick: little and often — small amounts every 20 to 45 minutes rather than one big hit — and train your gut by practising race-day fuelling in training, so the volume feels normal when it counts. Keep sodium and fluid coming too; both leave steadily in sweat.

Crossing the line feels like the end; physiologically it's a beginning — the window where your body rebuilds and comes back stronger. Recovery comes down to three jobs.

Refuel. Your glycogen tanks are drained and refill fastest right after you stop. In the first four hours, moderate-to-high-GI carbohydrate at about 1.0–1.2 g per kilogram per hour restocks them most efficiently — and delaying by a couple of hours can cut that rate roughly in half.

Repair. Hard efforts micro-damage muscle. Around 20–40 g of protein (roughly 0.3 g/kg) within about two hours provides the building blocks, with muscle protein synthesis peaking in the first few hours.

Rehydrate. You finish lighter than you started — that's fluid. Replace about 150% of what you lost, with sodium to help you hold it. Glycogen is stored with water, so refuelling and rehydrating work hand in hand.

Everything above, in one place. Use body weight to turn the per-kilogram figures into your own numbers.

A note on caffeine: some Krono gels and bars are caffeinated (citrus and Maple & Coffee gels, Chocolate & Espresso bars) — great for a pre-race or late-effort lift, but choose caffeine-free options if you're sensitive, and limit caffeine during pregnancy or for young athletes. These are general guidelines; your ideal numbers depend on your body, your sport and your gut, so test your plan in training first.