It’s heatwave season and soaring temperatures are adding an extra challenge to our workouts. How can you mitigate the effects, stay cool and keep exercising?
To be able to perform well in the heat, you need to be efficient at shedding heat and replacing lost water – but how exactly?
What happens in the body when you exercise in the heat?
The fatigue and loss of power you experience during very warm weather workouts is caused by two main factors: a rise in core body temperature and changes in your metabolism. Both the exercise itself and the air temperature and humidity can increase your core body temperature, putting stress on your cardiovascular system.
To help cool itself, your body sends more blood to the skin. This leaves less blood available for your muscles, and your heart has to work harder. Losing fluid in the form of sweat through the skin means blood volume decreases and your heart’s stroke volume decreases.
The most effective method of getting rid of excess heat during exercise is sweating, whereby the moisture on the surface of your skin cools you down as it evaporates. Staying on top of your hydration is crucial when exercising in the heat.
Hot conditions plus dehydration can lead to a drop in performance and, at worst, a dangerous rise in your core body temperature. If your body’s temperature exceeds 39ºC, you’ re at risk of developing heat-related illness – heat stress, heat exhaustion and heatstroke – stated in ascending order of severity.
Generally, performance starts to decrease when you lose 2% of your body weight as fluid through sweating. You may see anywhere between zero and 20% drop in performance.
- Reduce the duration and intensity of your workout.
- Exercise early in the day or later in the evening to avoid the worst of the heat – avoid exercising in the hottest part of the day
- If you’re exercising outdoors, seek the shade as much as possible.
- Sip an ice-cold drink or ice slushy (crushed ice + water) just before you exercise – this will pre-cool your body
- Pour or spray water over your skin to aid heat evaporation
- Put ice cubes inside your helmet, socks or jersey.
Make sure you’re hydrated
Dehydration is a key factor in heat-related illness. Staying hydrated helps your body sweat so will help lower your core temperature. Ideally, you should drink enough so that you keep your fluid loss below 2% body weight. That’s equivalent to a weight loss of 1.4kg for a 70kg person.
If you’re doing exercise that lasts less than two hours, where sweat losses are relatively small, you should only drink when thirsty. Over-hydrating can be as problematic as dehydration, causing a potentially dangerous imbalance in the body’s salt levels.
But if you’re sweating heavily or exercising longer than 2 hours you may need to be more proactive in your drinking strategy to avoid becoming dehydrated.
Can electrolytes help performance?
Although you lose electrolytes in sweat, you don’t need to replace them during workouts of less than two hours. You have enough sodium in your body to replenish sweat losses. By taking extra sodium in tablets, you could be pushing your overall salt intake too high. Only athletes sustaining heavy sweat losses, for example during workouts or races of longer than two hours are likely to see any benefit. But even then, the benefit is on longer-term sodium balance, not performance in any single event. It is a good idea to replace sodium after exercise, though most of us have plentiful salt in our regular daily diet to cover these needs.
Riders who suffer from cramps during long, hot rides, sportives or races often blame poor hydration or lack of electrolytes. However, recent studies have indicated that this isn’t always the case, and the exact reason for cramping is still unknown.
Heat adaptation training
If you know you’ll be racing in hot, humid conditions, doing heat adaptation training a few weeks beforehand will help you perform better.
If you can’t travel to a hot country before your race, the alternative is to simulate the conditions by wearing extra clothing while training or immersing yourself in a hot bath (40ºC) for 45 minutes.
You’ll need to raise your core temperature by 1.5ºC for at least 60 minutes daily for 10 – 15 days until a few days before your target race.
How do you know whether you know whether you are heat adapted? Your resting and exercise heart rate will be lower for the same power output, and you’ll start sweating earlier in your session or at a lower ambient temperature.
This is an abridged version of my feature in Cycling Weekly https://www.cyclingweekly.com/fitness/how-to-beat-the-heat-cooling-strategies-explained
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