From Julie Moss in 1982 to Jodie Swallow in 2013 via Chris Legh in 1997, the history of Ironman World Championships is littered with triathletes succumbing to dehydration in their quest for the sport’s ultimate accolade.
And it’s not just the athletes at the pinnacle of tri that are wilting in their 226km Hawaii journey, with the 1,000 competitors at Nottingham’s Outlaw being subjected to 30°C conditions in 2013.
So whether you’re racing eight or 17 hours at Hawaii or Holme Pierrepont this year, you’ll need a finely-tuned nutrition strategy to achieve your long-distance goals. Given the countless variables that influence performance – including how much you sweat and its composition, the conditions, type of course, body weight, athletic efficiency and experience – no one-size-fits-all approach can be applied. But there are key factors that you can analyse to prevent Mother Nature ruining your best-laid plans come the big day.
While sweat rate and composition is situation- and person-specific, recent research by the American College of Sport Medicine highlights that sweat rates double between winter and summer, with other factors including clothing, exercise intensity/duration, humidity and body weight all having an additional effect.
Aside from sweat, fluid is also lost as we breathe and when we go to the toilet, with an average fluid loss for men of 1.1ltrs/hr during exercise in the heat. But the body also partially hydrates itself by releasing water as we burn carbohydrate for energy, meaning that body weight loss might not be completely analogous with body water loss.
It’s often quoted that a 2% loss in body weight will reduce performance, yet studies show Ironman athletes can lose 3–6% of their body weight during an event without any clinical signs of dehydration.
This is because cognitive and performance reductions as a result of dehydration are also linked to a rise in core temperature. So the common advice to avoid 2% losses in bodyweight are appropriate when exercising indoors, but such losses can be safely tolerated outdoors (where the wind can help us to keep cool), assuming athletes begin their exercise hydrated.
A word of caution for female triathletes, however, as a recent study showed that performance declined during exercise in the heat (over 30°C) between days 14 and 28 of the menstrual cycle, as a result of a higher resting core temperature. Drinking ice-cold drinks may combat this, as they’ve been shown to have a cooling effect.
There’s a small selection of research that suggests adding small amounts of whey protein to sports drinks can improve your heat tolerance. But until there’s more literature available, for the majority of us it’s recommended to stick to the basics (drinking and keeping cool) that provide the vast majority of the performance benefits when racing in the heat. So try to include 140–750mg of sodium per litre during strenuous heat-affected exercise and consider protein only if you’re a top-level Ironman athlete looking for marginal gains.
Much has been made of not over-drinking, with the message ‘drink to thirst’ becoming popular. But triathletes should remember that dehydration isn’t ideal either. One 2012 study showed that balance and foot placement were significantly affected when athletes were exercising while dehydrated in the heat. This will have obvious negative performance connotations and increase the risk of injury, in addition to the dizziness, headache and sickness that may also be experienced.
How much to drink is a hotly-debated topic. Yet, by comparing studies, we can see that our bodies can’t process much over 200mls/20mins in the heat, while in cold conditions even around 300mls/hr shouldn’t cause any negative health issues. Therefore, stay hydrated from the start of exercise, drink 300–800mls/hr depending on the conditions, and add sodium to aid the utilisation of fluid. You can use thirst to dictate where you are in this range, but don’t rely on it alone.
You can also prepare for strenuous exercise in the heat over the days before, by drinking slightly more, adding small amounts of salt to your fluid or foods and monitoring your morning urine colour. Your first pee of the day gives the most accurate indication of your hydration status and should be pale to straw-like in colour.
Whether nutrition strategies should change when racing in the heat is still a contested issue. Consuming carbohydrate during exercise in the heat hasn’t been found to increase core temperature, so the best advice is to follow normal fuelling recommendations, but increasingly emphasise hydration the longer you predict your race time to be.
As we said in the introduction, long-distance nutrition is person-specific and depends on many factors, but athletes should look to drip-feed energy in evenly from the end of the swim at a rate of 30–60g of carbohydrate per hour. What form this takes is up to you, but the more processed higher-GI carbs found in energy gels and bars tend to be the triathlete’s fuel of choice.
While British researchers have also highlighted that you can adapt to heat stress to some degree, sweat rates don’t decrease as heat acclimatisation occurs. In fact, they may actually increase as the body learns to cool itself more effectively. Therefore hydration strategies still need to be maintained at higher rates than when exercising in cooler climates.
Acclimatisation, suitable clothing and a regular intake of cool drinks containing added sodium will all help us to battle the heat more effectively. But remember: the longer you’re out there, the more it becomes paramount to maintain a good rehydration strategy.
For lots more long-distance advice, head to our Training section