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Cycling In Hot Weather

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Cycling in the heat always seems preferable to cycling in the cold, but it’s potentially far more dangerous.

Why?

Simplistically put, it’s because you’re adding heat to heat, making it harder to maintain your 37°C core temperature.

This article tells you how to stay safe when riding in hot weather.

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Why Riding In The Heat Can Be Dangerous

When cycling in hot weather, your heart rate goes up as it increases blood flow to the skin. It does this to dissipate heat and moderate core temperature, but it’s easy to overwhelm this system as muscle and skin compete for blood flow.

Your core temperature only needs to go up by a few degrees centigrade to put your health and even your life in danger.

This danger manifests itself in two stages: heat exhaustion and heat stroke. They are two sides of the same perilous coin, though not everyone experiences or notices heat exhaustion before getting heat stroke.

Heat Exhaustion – 38-39°C

Heat exhaustion is always a precursor to heat stroke, even if some people skip this stage. It occurs when your core body temperature reaches 38°C or 39°C.

If you experience any of the following symptoms when riding in extreme heat, you should stop immediately, preferably in shade, and allow yourself to cool down:

  • Dizziness and feeling faint
  • Excessive sweating
  • Cool, pale and clammy skin
  • Nausea or vomiting
  • Muscle cramps
  • Poor coordination
  • Weak pulse
  • Headache

These symptoms will usually pass within 20-30 minutes, but you may feel weak and disoriented afterwards and should be wary of cycling in heavy traffic.

Although elite athletes tend to be more resistant to hot weather, even they can suffer its effects. Scottish runner Callum Hawkins collapsed from heat exhaustion while competing in the 2018 Commonwealth Games.

Video: Signs Of Heat Exhaustion

Heat Stroke – 40°C and over

If you push on through heat exhaustion, or even if you don’t experience it, heat stroke may occur. This can lead to a coma, brain damage or death, so it’s not trivial.

The symptoms of heat stroke are not the same as heat exhaustion:

  • No sweating (body stops sweating at this point)
  • Hot, dry skin
  • Bad headache
  • Rapid, strong pulse
  • Nausea or vomiting
  • Seizures
  • Loss of consciousness

A heat stroke is a medical emergency, so if you think you or a riding companion has gone past the point of heat exhaustion, call an ambulance.

Even top cyclists can get heat stroke. Young Belgian rider Enzo Wouters collapsed with heat stroke in the U23 World Championships road race in 2016.

Typically, the cyclists you see on TV undergo a meticulous hydration regime at the hands of their team nutritionists. And drinks are in constant supply during a race from team cars and roadside soigneurs.

Nevertheless, they still get dehydrated.

Video: What Happens When You Get Heat Stroke?

Heat Stress & The Body’s Response

We’ve described what can happen to you if you start overheating, but what’s going on in the body leading up to that point?

Heart Beats Faster

Cycling on a hot day, your heart rate is likely to increase by 10 to 20 bpm above the norm—your norm—within a short space of time.

Since this increase in heart rate is closely related to sweat rate and dehydration, you can try countering it by riding less intensely and drinking enough to replace lost fluids. You shouldn’t gain weight during a ride.

Blood Flow

When you begin to exercise, your “cardiac output” increases. This is your heart rate x stroke volume (the amount of blood being ejected with each beat).

At about 40-60% of maximum intensity, the stroke volume in most people plateaus and cardiac output increases by heart rate only.

During hyperthermia, stroke volume reduces slightly despite significant increases in heart rate and skin blood flow. A reduction in stroke volume and cardiac output theoretically leads to fatigue through a drop in oxygen delivery.

Oxygen delivery = cardiac output x arterial oxygen content.

Skin blood flow sharply curtails once core temperature reaches around 38°C. Thus, one of the body’s heat-stress defenses stalls, even if you’re still getting hotter.

5 Tips To Stay Cool & Safe When Riding Your Bike On Hot Days

Heat exhaustion or heat stroke are difficult to defend against if factors conspire against you. But you can do things to reduce the risk.

1. Stay On Top Of Hydration

If you want to avoid heat exhaustion or heat stroke, you should be careful to stay hydrated off the bike as well as on. Most adults require between 2 and 3 liters per day for good hydration. Don’t separate this need from bike rides.

The body becomes very efficient at sweating as you become fitter, which in turn cools you down by evaporation. But the fluids you lose during this process must be replaced to retain bodily function and maintain cycling performance.

Adequate fluid replacement during exercise helps to counteract increases in heart rate during hot weather, too.

Read more: Our guide to bike water bottles

Video: Hydration Tips Every Athlete Needs To Know

2. Eat Sodium

You lose far more sodium than any other electrolyte through sweat, and low blood sodium levels (hyponatremia) can induce headaches, cramps, nausea and confusion.

Not all electrolyte drinks contain enough sodium to reverse these symptoms. This is something you can look at if you have a high concentration of sodium in your sweat, indicated by salt crystals left on your skin or clothing after exercise.

As well as paying attention to salt content in drinks, you can eat salty snacks during or after a ride (e.g. pretzels, crackers, peanut butter.) This helps keep the brain sharp and the body reactive.

Video: Why Sodium Is Important For Athletes

3. Wear A Heart Rate Monitor

Many people don’t like wearing a heart-rate monitor because they link it with taking cycling too seriously and not enjoying their ride. However …

Cyclists who routinely ride fairly intensively, as many amateurs do, can find their heart rate pushed to “threshold” levels in extreme heat as they try maintaining their usual speed and performance. By definition, that’s sustainable for one hour.

If you see that your heart rate is at an unsustainable level in hot weather, you can bring it back down by curbing intensity and regularly hydrating.

Heart-rate monitors aren’t only for interval training. They’re good for safeguarding your health.

Video: Increased Heart Rate In The Heat

4. Go Out Earlier

It’s an obvious one, this, but an early-morning bike ride is always cooler than riding in the mid-afternoon. Riding habits are hard to break, so you may have to adjust your sleep times, breakfast time and clothing to get out early on your bike.

If you need extra motivation for this, on top of avoiding heat exhaustion, a scientific study by the University of Bath suggests there are significant health benefits to riding before breakfast.

Periodic pre-breakfast bike rides can lower risk of cardiovascular disease and type-2 diabetes. Fasted rides such as this are generally low intensity for 60-90 minutes.

Video: Early Morning Bike Ride

5. Acclimate And Get Fitter

Improving your aerobic fitness level helps your body to adapt quicker to high temperatures. Even with this fitness, you still need to acclimate to hot weather if you’re unused to it. Don’t ride fast in crazy heat if you’re unfit.

Cycling regularly for up to two weeks in high temperatures will help you to acclimate. Keep intensity low and duration relatively short during this time. Passive acclimation like sitting in a sauna or sunbathing doesn’t work as well.

You also need to maintain your hydration regime while acclimating. Deliberate dehydration is not useful in this process and is potentially harmful.

Video: Heat Acclimation Cycling Tips

The Heat Is….Off

The info above should help you offset the dangers of cycling in hot weather. Remember to hydrate on and off the bike, listen to your body and take it easy.

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Bike Push - Mark W
Mark W
I’m a cycling enthusiast, and the founder and chief editor of Bike Push. If I’m not working on this website, then I’m out on the bike clocking up the miles. I want to help others get the most out of cycling.

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