Running in hot weather

This page provides general guidance on running safely in warm weather, whether you are training or taking part in an event. Some advice — such as allowing your body to adapt gradually — applies to training and cannot be rushed in the final days before a race.

On event day we have our own medical team on site throughout. If you feel unwell at any point, your first port of call is the nearest member of the event team — a volunteer, marshal, security steward or medic — who will get help to you. Always follow the instructions given by the event team, which take priority over anything on this page.

Running in hot or humid weather places additional strain on your body. The risk can be particularly high when temperatures rise suddenly and you have not had time to become accustomed to the heat.

Check the weather forecast before training or travelling to an event. If conditions are unusually hot, be prepared to slow down, change your plans or stop altogether.

Before running

• Avoid hard training during the hottest part of the day, normally between 11am and 3pm.

• If possible, run early in the morning or later in the evening and choose a shaded route.

• Allow your body time to adapt gradually to warmer conditions. Do not begin with a long or intense session.

• Start your run normally hydrated. Your urine should generally be a pale-yellow colour.

• Do not run if you have a fever, vomiting, diarrhoea or otherwise feel unwell.

• Some health conditions and medicines can affect how your body responds to heat. Seek medical advice if you are unsure whether it is safe for you to exercise.
  

Dress for the conditions

Wear lightweight, loose-fitting and breathable running clothing. Avoid unnecessary layers or costumes that may prevent heat escaping. Wear a cap or visor if helpful, together with suitable sunglasses. Protect exposed skin with a broad-spectrum sunscreen and follow its application instructions.

Slow down
Hot weather is not the time to chase a personal best.

Reduce your pace from the start and use how you feel — rather than your usual target pace — to judge your effort. Walking, taking a break or stopping completely is always acceptable.

Drink according to your needs

Start well hydrated and drink according to your thirst and the conditions. Individual requirements vary according to the weather, your pace, your size and how much you sweat. Water is suitable for many runners. A sports drink containing carbohydrate and electrolytes may be useful during longer sessions, particularly if you sweat heavily, but it is not necessary to replace every drink with a sports drink. Do not force yourself to drink large amounts. Drinking more fluid than your body needs can cause hyponatraemia, when the sodium level in the blood becomes dangerously low. This can lead to confusion, seizures and, in severe cases, death. Avoid salt tablets unless they have specifically been recommended by a qualified healthcare professional.

Cooling yourself

Running in shade, reducing your pace, wetting your skin and moving to a cooler place can all help your body lose heat. Tipping water over your head and body is an effective way to cool down.

At an organised event, use any cooling facilities as directed. Where only drinking water is provided, follow any guidance you are given on whether it may also be used for cooling.

Signs of heat exhaustion

Heat exhaustion can include:

• unusual tiredness or weakness

• dizziness or headache

• nausea or vomiting

• heavy sweating

• pale or clammy skin

• feeling very thirsty

• cramps in the arms, legs or stomach

• irritability

• a raised temperature

If you experience these symptoms, stop running immediately and tell the nearest member of the event team — a volunteer, marshal, security steward or medic. Move to a cool or shaded place, remove unnecessary clothing and begin cooling down.

Drink water or an isotonic drink if you are fully alert and able to swallow.

Do not continue running simply because you begin to feel slightly better.

Heatstroke is a medical emergency

Warning signs of heatstroke include:

• confusion, unusual behaviour or severe agitation, loss of coordination, staggering or repeatedly stumbling, a very high temperature, rapid breathing or a rapid heartbeat, collapse or loss of consciousness, a seizure. Someone with heatstroke may be sweating heavily or may have hot skin without sweating. Do not wait for sweating to stop before seeking help.

If you notice these symptoms in yourself or another person, get help immediately from the nearest member of the event team — a volunteer, marshal, security steward or medic. Our own medical team is on site throughout the event and will arrange urgent help. The person should be moved into shade and cooled urgently while help is on its way.

Do not give food or drink to anyone who is confused, having a seizure, unconscious or unable to swallow safely.

Event medical personnel may stop a participant from continuing if they believe doing so would put the participant’s health at risk.

After finishing

Keep walking gently if you are able, rather than stopping suddenly. Move out of direct sun, cool down and change out of wet clothing when practical. Drink gradually according to your thirst and eat normally. Do not consume a large quantity of fluid immediately after finishing.

If you feel dizzy, confused, unusually weak or unwell, tell the nearest member of the event team straight away — a volunteer, marshal, security steward or medic.

Who may be at greater risk?

Heat-related illness can affect anyone, including experienced and well-trained runners. Risk may be higher for people who:

• are not accustomed to exercising in warm conditions are unwell, dehydrated or recovering from illness have previously experienced heat-related illness have certain medical conditions take medicines that affect hydration, sweating or temperature regulation wear heavy clothing, costumes or equipment begin too quickly or exercise harder than the conditions allow.
  
  If you have previously experienced heatstroke or have concerns about a medical condition, seek advice from your GP or another qualified healthcare professional before running in hot weather.

Further information: NHS guidance on heat exhaustion and heatstroke.

This information provides general safety guidance and is not a substitute for individual medical advice. If you are taking part in an organised event, always follow instructions issued by the event team and medical professionals.