From the December 2012 issue of Runner’s World

It’s not just water that pours from your pores. Knowing precisely what you lose, and how to replace it, is key to recovery and performance

By Wesley Doyle

As with many things in running, sweating is deeply personal. The amount that runs out on the run varies widely from runner to runner. It also depends on intensity and conditions. In one of the highest documented sweat rates in sport, for example, Alberto Salazar lost an average of 3.7 litres an hour during the 1984 Olympic Marathon.

Along with lost liquid go minerals, known as electrolytes, essential for bodily function. “You lose about 20 different electrolytes when you sweat,” says Dr Raj Jutley, chief medical officer at Precision Hydration UK, a team of experts in performance hydration who conduct precision personal sweat profiling. “Some are trace quantities you needn’t worry about; others you need to replace quickly as your body doesn’t have a store.”

The major four are sodium, potassium, magnesium and calcium. Like your volume of sweat, the amount of electrolytes lost per litre differs from person to person – in some cases up to nine-fold. That means one-size-fits-all electrolyte sports drinks only cater for average perspiration. So if you find yourself overly fatigued, dizzy or cramping you may not be replacing what you’re losing. Use our guide to see exactly what you’re leaking, and how to replace it to aid recovery and performance.

1 Potassium
Like Sting in stalker mode, potassium is there every move you make, every step you you take. “It’s important for nerve conduction and energy generation,” says Jutley. “A deficiency is known as hypocalcaemia and can result in nausea, muscle fatigue and weakness.” But if you’re well stocked, you’d have to sweat about 16 litres before your stores run out. Make sure your diet includes sweet potatoes, tuna, squash, bananas, leafy green vegetables and yoghurt, which the Institute for Optimum Nutrition, UK, cites as the foods richest in potassium.

2 Calcium
Essential for exercise performance, calcium “is involved in muscle contraction and relaxation, as well as nerve conduction – things that keep you moving”, says Jutley. “Low levels can result in stiffness and cramping and it would only take about five litres of sweat to lose enough to cause a deficiency.” Your body does have a vast supply of calcium stored in your bones, but with a typical loss of 28mg per litre through sweat, runners should ensure they get plenty of calcium-rich dairy in their diets.

Just as importantly, look to improve your body’s absorption of the mineral, which is aided by vitamin D. As we’re supposed to get the ‘sunshine vitamin’ with the help of sunshine, unless you can winter in the Seychelles it’s best to make sure your diet is high in D-rich oily fish and eggs, or take a supplement.

3 Magnesium
Like potassium, “this is vital for muscle contraction and energy production, and a deficiency can lead to dizziness, fatigue and depression,” says Jutley. “You’d have to sweat a lot before your stocks ran low – about 15 litres.” Ensure your recovery menu replenishes your stores with pine nuts, brown rice and – yes, someone up there loves us after all – dark chocolate.

4 Sodium
“Sodium – or salt – is the key active electrolyte lost in sweat,” says Jutley. And its prime function in your life isn’t to taste good on your chips. “Salt plays a crucial role in muscle and nerve function, and is essential for maintaining your fluid levels,” he explains. “Deficiency can result in weakness, nausea, muscle fatigue and cramping.” It can also hinder rehydration, in extreme cases causing seizures and even death. Typical sodium loss ranges between 230-1700mg per litre of sweat, depending on activity intensity. “The best way to maintain performance and aid recovery is to replace like-for-like,” says Eliot Challifour, director at Precision Hydration. “But most rehydration products are pitched at average sweaters, so people who lose very high amounts of sodium – ‘salty sweaters’ – would have to drink a lot of them, which would mean taking on too much fluid.”

Precision Hydration has developed a test that pinpoints precisely how much salt you lose; our test (below) won’t give you a figure, but will tell you if you’re a salty sweater. If you are, look for high-sodium products such as Endura Magnesium Rehydration Formula (A$39.95; NZ$47.95 endura.com.au; endura.co.nz)

And the rest…
Other bodily essentials lost in sweat are zinc, copper, iron, chromium, nickel and lead. They’re lost in such small quantities that you don’t need to panic about actively replacing them on the run – but topping up on zinc, found in all meat, shellfish and dairy, around intense blocks of training will keep your immune system ticking over.

SWEAT TEST
How much do you sweat?
“There’s a simple way of calculating your sweat rate,” says Mayur Ranchordas, head of nutrition at Sheffield Hallam University, UK. And no, it’s not counting how many treadmills are free around you. “Weigh yourself before a 60-minute run, drink nothing on the run, finish, towel off any excess sweat, then weigh yourself again. Each gram you lose equates to a millilitre of fluid, giving you your hourly sweat rate.”

Are you a ‘salty sweater’?
Finding out your sweat makeup is a little more complicated. “You can get a good idea as to whether you’re a ‘salty sweater’ by looking at your gear after a run,” says Challifour. “White marks are a sign that you’re losing above-average levels of sodium. On the run, stinging when sweat runs into your eyes and cramping also indicate high salt loss.”

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