Dr Armstrong: Salt and the athlete

Dr Stuart Armstrong, RoadCycling.co.nz's newest Kiwi coach, begins his regular series by discussing information and mis-information about salt.

There is a lot of mis-information about salt out there. Namely what it is and isn't responsible for.  As athletes we worry about low salt (hyponatraemia), the non-athletic population worry about high salt.

Today I am just going to talk about low salt and how it affects us as athletes.

By now everyone should be familiar with the dangers of drinking pure water during endurance events and the risks of hyponatraemia. Despite this, some athletes still get this wrong.

13% of competitors in the 2005 Boston marathon were found to be hyponatraemic due to drinking too much water.

Basically it comes down to sweat and how this loss should be replaced.

Replacing sweat fluids

We sweat in order to cool the body down. Sweat does this by evaporating off the skin. It contains many elements, but primarily it is high in salt (sodium chloride.)

If you are sweating a lot and replace this with pure water then it is logical you will become acutely salt deficient. This rapid onset hyponatraemia can lead to swelling of your ankles and feet, confusion, nausea, vomiting, headache and weakness. (Remember Craig Barrett?). If it is not recognised and treated it can progress to coma, fits and ultimately death. Not something to be taken lightly!

This is why you are frequently weighed before and after an endurance race. If your weight goes down then you are dehydrated – as to be expected. If on the other hand your weight increases by more than a couple of kilos there is a good chance that you have taken too much pure water and are hyponatraemic.

In general never replace sweat loss with pure water. Commercial drinks have varying amounts of salt added and are a good alternative. 1/2 teaspoon (2.5grams) of salt contains 1g of sodium and 1.5 grams of chloride. Sweat contains 0.25-1.5g of sodium per liter. Commercial fluid replacement drinks usually contain 0.4-0.6 grams of sodium per liter. A higher concentration of salt is often unpalatable.

Pre-race preparation

It is also important to increase your salt intake in the few days leading up to a race. This can easily be done by using table salt or commercially available salt tablets.

Your average sweat rate during moderate exertion in temperate climates is around 1L per hour. Obviously this will be higher with exercise in heat or high intensity exercise. It is important to replace both your fluid and sweat loss on any training ride >1 hour.

Salt myths

There are a few myths surrounding the effects of salt loss on athletes.

Everyone knows that if you cramp during a race it is either due to acute salt deficit or dehydration. Stopping, taking a salt tablet and some fluids will sort the problem out right.... Wrong!

There have been many studies looking at exercise associated muscle cramps in ultra distance events (primarily by Schwellnus) and they have conclusively proven the cramps are due to neither salt depletion or dehydration. If you are cramping from salt deficit then you have muscle cramps everywhere – legs, arms, face, back.... Not just the muscles you are using (or overusing!)

Personally I think you cramp because you have pushed your muscles beyond what they are capable of, it is purely a sign of fatigue. If you ease off when you first notice the muscle tightening or "twitching" then you will likely avoid having to stop because of full blown cramp.

Let's now look at chronic (long term) salt deficiency. This is a condition that is not widely known or written about.

It is a common myth that with time and exposure to exercise in the heat your body/sweat glands adapt and you produce sweat with less sodium. This is not true. You sweat out less salt because with time your body becomes deficient in salt. So if you think you don't need to salt supplement because your sweat isn't salty you have it all the wrong way round and you should be the one taking salt tablets not your buddy with salt crusts on his race suit.

I have treated an athlete with symptoms of chronic salt depletion – muscle cramps in his arms and legs and pelvis at night and dizziness on standing due to low blood pressure. He has responded very well to salt loading with 1-2 teaspoons salt twice a day and education correct fluid and salt intake during training.

Summary

In Summary salt is important to all athletes.

Acute deficit can be a very serious condition and can be easily prevented. Exercise associated muscle cramps are not due to salt deficiency. Your sweat glands will not adapt to exercise over time, as a result you can develop chronic salt deficiency. This commonly goes unrecognized and while not serious can cause its own problems as outlined above.

Any and all information obtained on roadcycling.co.nz should not be taken as a recommendation for treatment of any particular person or patient. Should you think that you, or any other individual, might require treatment for one of the conditions described here, please seek the advice of a qualified physician or doctor. Please be advised that using the information provided here in no way means that a doctor-patient relationship has been established between you and the author of the information provided on this website.

April, 2010

Other articles by Dr Armstrong

• Winter ills

About Dr Stuart Armstrong.......
Dr Armstrong qualified from Glasgow Medical School in 2002. He moved to NZ in 2003 and has spent the last 7 years working as an Acute Medical Registrar in numerous hospitals around NZ. He has recently passed his Sports Medicine Fellowship exams.

Dr Armstrong is an avid triathlete. He has completed 5 Ironman distance races to date, as well as representing NZ at the World Long Course Championships in 2009.

He is also the founder and owner of Elite Race Rentals which rents the latest Zipp race wheels and Powertap training wheels. Be prepared to rip up the road like the pros. Just think of those minutes melting off your bike time.

You can find out more at www.eliteracerentals.co.nz or email him at:  This e-mail address is being protected from spambots. You need JavaScript enabled to view it