Column 36, January 2010

Taking on the heat this summer

We’ve certainly been blessed with beautiful weather this summer, but if you’re out running in the heat, or racing in it - as we experienced at the Tauranga Half Ironman earlier this month – there’s a few important tips that will help you avoid disasters.

Overheating and dehydration can at best negatively affect your performance, and at worst cause heatstroke and even death.

Whilst the temperatures in this country are mild compared to those closer to the equator, the combination of humidity and high air temperature – giving the ‘apparent’ or ‘feels like’ temperature - can be enough to create problems for runners. For example, an air temperature of 27 C with a relative humidity of 90% feels like 30.7%, a temperature likely to cause heat cramps or heat exhaustion with exercise.

When the body heats up internally, more blood is sent to the skin to create sweat, which helps cool the body. However, while running, the muscles demand oxygen, meaning less blood flows to the skin, causing overheating.

A dilemma occurs within the body when we try to continue to run at high intensity. Either the blood (carrying oxygen) goes to your muscles to keep up the pace and you start to overheat due to less blood going to the skin for cooling – OR – the blood goes to the skin for cooling, and less goes to your working muscles, causing you to slow down, and dehydrate more quickly.

Precautions for running in the heat

Dress light and loose – Light coloured clothing reflects the suns rays better, while the latter takes advantage of any breeze to help cool the body. Sports-specific synthetics are better than cotton at wicking away moisture too.

Start the run hydrated. This means minimising diuretics such as caffeine and alcohol, as well as antihistamines, antidepressants and anti-inflammatories if possible. Guzzle 500ml+ of water 1hr before your run to optimise hydration.

Allow time to acclimate. For the first few weeks of hot weather it is best to start by walking or doing shorter runs (30 minutes) in the heat of the day, and saving longer runs and speed sessions to early mornings or evenings.
If you’re in air-conditioning all day you’re not going to acclimatize either. However, exposing yourself to hot weather for as little as 30 mins a day is enough to induce changes that make the body more tolerant of heat stress.

Maintain hydration during runs. Don’t wait till you’re thirsty to drink, as you will already be dehydrated. Increased sweating means loss of fluid AND electrolytes, so every 15-20 mins plan to consume an easy tolerated amount – ~250mls - of either sports drink for long runs (>90mins), or electrolyte water (eg Nuun) during shorter runs (30-90mins), rather than straight water. The flavour in these drinks makes them easier to consume, and the sodium/carbohydrate content increases water absorption, whilst preventing fluid over-load (hyponatremia).

You will need to plan your run around drink stations (this even includes some friendly pubs on my run route!), or consider taking a camelback. During races make the most of drink stations.

Choose running socks carefully. Heat, means sweaty feet and an increased chance of blistering. Thin, synthetic blends are best, such as Thorlo lite running, Nike DriMax, Adidas Climacool, and Wright sock – a double layered sock which allows movement between the layers, reducing friction and blister formation.

Measure your particular fluid losses. Weighing before and after running in the heat will give you a better idea of your individual sweat/fluid losses. To ensure rehydration, aim to consume 125-150% of your fluid deficit over the next 2-6 hours. For example, if you lost 1kg during your run you will need to drink 1250-1500mls to replace. Ideally, however, aim to increase your fluid consumption by 1 litre during a similar run, to prevent dehydration.

Screen UV’s with protective lotions, clothing and accessories. A fairly recent study found more abnormal moles and lesions in marathoners than non marathoners, and reported that only 56 of runners use sunscreen regularly. A sweat proof sunscreen with a broad spectrum SPF of 30 should be applied 20mins before runs.

Also look for new run garments with a high SPF rating, as some fabrics provide only the protection of an SPF 7. These garments are light enough that full length sleeved tops remain cool whilst preventing damage from harmful UV rays. White caps made from synthetic functional material and mesh will screen rays from your noggin without holding heat, whilst sunglasses defend our eyes from forming cataracts, and prevent headaches brought about from squinting and exposure to bright light.

Lower your speed and expectations. In training and races realise that you won’t be able to run as fast on hot days as cool days. Start slower, and gradually increase the pace at the half way mark to avoid pushing your body over into the danger zone.

9. Heed the signs of heat illness;

Headache or intense heat build-up in the head
Confusion or lack of concentration
Loss of muscular control
Over-sweating followed by cessation of sweating
Hot and cold flashes
Upset stomach, muscle cramps, vomiting, dizziness

   10. End with a cold dunk. There’s no greater feeling
           than a cold watery dip after running on a
           scorching day. Plan to start a few of your weekly
           runs from a pool, stream, beach, and enjoy the recovery benefits of a long, cold plunge.

Well I’m off for my run/dunk… stay cool out there!

Marnie Oberer

Marnie Oberer as an Expert columnist.

Taking on the heat this summer

Precautions for running in the heat