Training in the heat: how to exercise safely through a Dubai summer

Why heat changes the session

Muscles produce heat when they work, and the body gets rid of it mainly by evaporating sweat. In hot, dry air this works well. In hot, humid air, sweat drips rather than evaporates, and the cooling fails. Coastal Gulf summers combine temperatures above 40 degrees with high humidity, which is the hardest combination there is.

Two consequences follow for training.

• The same pace costs more. Blood is diverted to the skin to shed heat, so the heart beats faster for the same work. Heart rate at a given speed can be ten to twenty beats higher than in winter.
• Dehydration builds quickly. Fluid lost in sweat reduces blood volume, which raises heart rate further and lowers the capacity to cool. Performance declines measurably once the loss passes about 2% of body weight.

Train by heart rate or by effort, not by pace, from May to October. See zone 2 training.

Acclimatisation: ten to fourteen days

The body adapts to heat remarkably well. Within about two weeks of repeated exposure, sweating starts earlier and becomes more abundant, the sweat contains less salt, plasma volume expands and heart rate at a given effort falls. The position stand of the American College of Sports Medicine gives 10 to 14 days of progressive exposure as the time needed.

A sensible progression for someone returning from a cooler country:

1. Days 1 to 4: 20 to 30 minutes of easy outdoor exercise at the coolest hour.
2. Days 5 to 9: 40 to 60 minutes, still easy.
3. Days 10 to 14: normal duration, with intensity reintroduced last.

The adaptation fades in two to three weeks away. After a summer spent in Europe, start again from the beginning.

Measuring your own sweat rate

Advice to "drink plenty" is useless when one person loses 400 millilitres an hour and another loses two litres. The measurement takes two minutes.

1. Weigh yourself, towel-dried and in minimal clothing, before the session.
2. Train for an hour, noting how much you drink.
3. Towel off and weigh yourself again in the same clothing.
4. Subtract the second weight from the first and add the volume drunk. Each kilogram is a litre of sweat.

The calculator above does the arithmetic and tells you whether you passed the 2% threshold. Repeat the test in winter and in summer: the two figures can differ by a factor of two.

What to drink, and how much

• Before. About 5 to 7 millilitres per kilogram of body weight in the four hours before: roughly half a litre for an 80-kilogram adult. Pale urine is the simplest sign that you start hydrated.
• During. Enough to keep the loss under 2% of body weight, and no more. Drinking far beyond your sweat losses dilutes blood sodium, a rare but serious condition seen in long events.
• After. About 1.5 litres for each kilogram lost, spread over the following hours, because part of what you drink is passed straight out.
• Salt. For sessions over an hour in the heat, or if your clothes dry with white marks, a drink containing sodium replaces what water alone does not.

For daily needs outside training, see hydration.

Arranging the day

• Dawn is the only outdoor window in summer. Temperatures are lowest just before sunrise. Evening air stays hot and often more humid.
• Indoor training is not a compromise. An air-conditioned gym, a pool or a shaded indoor track allows quality work that the outdoor heat forbids.
• Shorten and split. Two sessions of thirty minutes are safer than one of sixty.
• Dress for evaporation. Light, loose, pale clothing. A cap, and sunscreen that does not block sweating.
• Cool beforehand. A cold drink or a cool shower before a session delays the rise in core temperature.

Recognising heat illness

Heat exhaustion comes first: heavy sweating, headache, dizziness, nausea, cramps, a fast pulse, unusual tiredness. Stop, move to a cool place, lie down with your feet raised, drink, and cool the skin with water. You should feel better within thirty minutes.

Heatstroke is an emergency. The signs are a very high temperature, hot skin that may have stopped sweating, confusion, loss of coordination or loss of consciousness. Call an ambulance, and cool the person by any means while waiting.

Risk is higher if you are unacclimatised, unfit, unwell, short of sleep, or have recently had a stomach illness or drunk alcohol. See alcohol and training.

A note on Ramadan and travel

Training while fasting from fluids deserves particular care in hot months: keep sessions short and light, and place them shortly before the fast is broken or after it. After a long flight you arrive mildly dehydrated and unacclimatised at once, so the first two days call for easy indoor work. See jet lag and training.

A coach who trains clients in Dubai year-round adjusts the plan to the season as a matter of course. How the Club introduces you to one.