Cold-Weather Racing Needs More Fuel, Not Less — Here's Why and How to Adjust

The assumption that gets cold-weather racers into trouble

You trained through summer. You dialled in your gel timing. You know exactly how many carbs per hour your stomach can handle. Then race morning arrives and it's 7°C with a headwind, and you think: at least I won't have to worry about fueling as much.

That instinct is wrong. And it's one of the most common reasons runners bonk in fall and winter races despite having a plan that worked perfectly in warm-weather training.

The logic seems sound on the surface. Cold weather means less sweating. Less sweating means less fluid loss. Less fluid loss means less urgency. But fueling isn't just about fluid. Your muscles run on glycogen, and cold air changes the rate at which they burn through it.

Why your muscles burn more carbs in the cold

When the ambient temperature drops below about 10°C, your body shifts its fuel mix. Research on exercising in cold conditions consistently shows an increase in carbohydrate oxidation — the rate at which your muscles break down glycogen for energy — compared to the same effort in moderate temperatures.

There are three mechanisms at play:

1. Thermoregulation costs energy. Even before you start shivering, your body is working to maintain core temperature. Blood vessels constrict to preserve heat, your metabolic rate rises, and the extra energy comes disproportionately from carbohydrate rather than fat. This means you're dipping into glycogen stores before you've taken your first gel.

2. Shivering burns glycogen directly. If you're under-dressed at the start, or the temperature drops late in the race, shivering draws heavily on muscle glycogen. Even mild, imperceptible shivering during the first few kilometres of a cool morning race can accelerate glycogen depletion. By the time you reach the halfway point, you're further into your reserves than you'd be on a warm day at the same pace.

3. Cold air reduces the efficiency of fat oxidation. Your body's ability to use fat as fuel is partly temperature-dependent. When conditions are cool, the relative contribution of fat drops and carbohydrate contribution rises. For a marathoner running at the same pace, this can mean an increase of 10–20% in total carbohydrate burned over the course of the race.

The net result: you arrive at mile 18 with less glycogen than your training data predicted, even if your pace, effort, and gel timing were identical.

The sweat-rate trap

The other problem with cold-weather fueling is the connection between hydration and fuel delivery.

Most runners calibrate their drinking to their sweat rate. In warm weather, that means drinking frequently — and every time you drink, you also have an opportunity to take in carbs (from a sports drink or alongside a gel). In cold weather, you sweat less, so you drink less. And when you drink less, you also tend to eat less.

This creates a double problem:

• You need more carbohydrate per hour (because of the thermoregulation cost), but
• You're consuming less because your drinking cadence has slowed down.

If your fueling plan is built around "take a gel every time I drink," cold weather quietly dismantles it.

How to adjust your fueling plan for cold races

The good news: the adjustment isn't complicated. It just requires you to separate your hydration schedule from your fueling schedule — something every runner should do anyway, but especially in the cold.

Increase your carb target by 10–15%

If you've been fueling at 60g of carbohydrate per hour in warm conditions, target 65–70g per hour for a race below 10°C. If you're already pushing 80–90g per hour, aim for 90–100g. The exact increase depends on how cold it is, how long the race will take, and your body weight, but 10–15% is a practical starting range.

Decouple fueling from drinking

Don't wait until you're thirsty to take a gel. In cold weather, thirst is an even less reliable signal than usual. Set a timer or use distance markers to trigger fueling regardless of whether you feel like drinking. Every 25–30 minutes for gels, independent of your fluid intake.

Front-load your carbs slightly

Because glycogen depletion is accelerated in the cold, consider taking your first gel 5–10 minutes earlier than you normally would. If you usually start fueling at 35–40 minutes, shift to 25–30 minutes. This builds a small buffer before the thermoregulation tax kicks in fully.

Don't underdress to "warm up as you go"

Starting cold doesn't just make you uncomfortable — it costs glycogen. Wear a throwaway layer for the first few kilometres if needed. The small inconvenience of carrying or discarding a layer is worth it compared to the 100–200 extra kilocalories of glycogen you'll burn shivering through the first 5K.

Carry warm fluid if possible

Cold sports drinks are harder to drink in cold weather, and your GI system processes cold fluid slightly slower. If you're carrying your own bottles, room-temperature or slightly warm fluid is easier to get down and absorb. Race aid stations won't offer this, so plan your own supply for the first half at minimum.

A cold-weather fueling checklist

Use this before any race where the start temperature is below 12°C:

• Carb target: Increase by 10–15% over your warm-weather plan
• First gel: 25–30 minutes in (5–10 minutes earlier than normal)
• Gel cadence: Every 25–30 minutes by timer, not by thirst
• Fluid: Drink on schedule even if you're not thirsty — aim for 400–500ml per hour minimum
• Clothing: Wear a throwaway layer to avoid early-race shivering
• Pre-race meal: Same timing as usual, but increase carb portion by 10–15% (an extra slice of toast with honey, an extra 200ml of sports drink)
• Warm-up: Longer than usual to raise core temperature before the gun

What this means for your race-day plan

The problem with generic fueling advice is that it assumes stable conditions. But race day rarely matches training day — temperature, humidity, wind, and altitude all change the equation. A plan that worked at 22°C in August won't work at 8°C in November unless you adjust it.

This is exactly the problem Sweatr solves. Instead of giving you a single carb-per-hour number and hoping conditions cooperate, Sweatr builds your fueling plan from your actual wearable data — your training load, your sweat rate trends, your race pace, and the conditions on race day. When the forecast changes, your plan changes with it.

You can run the numbers yourself with a calculator and a weather app. Or you can let Sweatr do it automatically using the data your Apple Watch or Garmin is already collecting.

Your muscles don't care whether it's a warm day or a cold one. They care about glycogen. Make sure your fueling plan accounts for that.