How to Avoid Getting Ill When Winter Training: A Triathlon Coach's Guide

This article is general guidance, not medical advice. If you're unwell or have a health condition, speak to your GP.

Every January I get the same message from at least three athletes: "Coach, I'm full of cold. What do I do with this week?" One lost week isn't the problem. The problem is the pattern. Ill in November, again over Christmas, again in February, and the base you were meant to be building for spring is full of holes.

You can't make yourself bulletproof. But most of the winter illness I see across our athletes comes down to a handful of things you control.

Why endurance athletes get ill more in winter

It isn't the cold air. Respiratory viruses circulate more in winter, we spend more time indoors together, and short days mean our vitamin D drops. Stack a heavy training block on top of a full-time job, broken sleep and the Christmas social calendar, and your immune system is juggling a lot. Very long or very hard sessions add to that load. The real risk is total stress with not enough recovery.

1. Treat sleep like a key session

Sleep is the biggest lever you have. In one well-known study, people sleeping under six hours a night were roughly four times more likely to catch a cold when exposed to the virus than those getting over seven. Aim for seven to nine hours. If a 5:30am swim means you're running on six, the swim isn't worth it. Move it.

2. Don't train on an empty tank

Under-fuelling is an immune problem, not just a performance one. Take carbohydrate on board during long and hard sessions, and eat properly afterwards. Winter is not the time for aggressive weight loss. Build meals around protein, wholegrains and plenty of colourful fruit and veg (more on that in what triathletes eat in a day).

3. Take vitamin D from October to March

The NHS advises everyone in the UK to consider a daily 10 microgram (400 IU) vitamin D supplement through autumn and winter, because there isn't enough sunlight to make our own. It's cheap and simple. Check with your GP before taking higher doses.

4. Manage total load, not just training load

Your body doesn't care whether stress comes from VO2 intervals or a brutal week at work. When life spikes, training has to flex. I'd much rather drop one session than lose a fortnight. Watch for the early warnings: resting heart rate creeping up, HRV trending down, heavy legs that don't clear, a scratchy throat. Flag them to your coach.

5. Be boring about hygiene

Unglamorous, but it works. Wash your hands after the gym, the pool changing room and the train. Keep your hands away from your eyes and nose. Don't share bottles. Speak to your GP or pharmacist about the flu jab, especially if you're heading into a big spring race.

6. Get warm and dry, fast

Sitting in wet kit after a three-hour winter ride leaves you chilled and drained. Change straight away, get a warm drink in, and eat within the hour. On the grimmest days, the turbo is a perfectly good option (see our guide to training for triathlon through the winter).

If you do get ill: the neck check

Symptoms above the neck only, like a runny nose or mild sore throat? Easy, short sessions are usually fine. Anything below the neck, such as chest symptoms, fever, aches or an upset stomach, means rest. Never train with a fever. We've covered this in more detail in Should You Train With a Cold or Flu?

Consistency beats heroics

The athletes who have the best springs are rarely the ones who trained hardest in winter. They're the ones who trained most consistently. If you want a plan that flexes around real life and a coach watching for the warning signs, book a free consultation call or read more about our 1-2-1 triathlon coaching, marathon coaching and full coaching plans and pricing.

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