Performance Articles — 09 March 2012
Sweat Testing! How paying attention to fluid loss could help YOU!

After becoming an over heated mess at the Busselton Ironman in December 2011, I decided to really delve into the ‘why’s’ of what happened in great detail.

I have been fortunate enough to work with Rebecca Hay, who works in Sydney as a Sports Nutritionist in Sydney, who is very experienced in working with high level athletes and has done several Ironman triathlons herself. Rebecca and I have been working together as part of the 220 MAGAZINE TRIATHLON TEAM, who are following me for 6 months in the lead up to Port Macquarie Ironman. Rebecca is the nutritionist for the team.

During the race in Busso, with the hot weather and winds, it was very obvious I became dehydrated early in the bike. This then lead to a reduction in sweat rates, which obviously then lead to an increase of core body temperature. When this happens, the show is pretty much over, as it is very difficult to absorb any calories and even more difficult to replace the fluids that have been lost.

I know that I have been susceptible to this in the past and after I had the melt down in Busso, it prompted Rebecca and I to do some more investigation.

Firstly we did a very detailed fluid balance chart. This involves recording:

  • Pre training weight
  • Fluid add food taken in while training
  • Post training weight

Along with temperature and humidity.

I found this an invaluable exercise, as it taught me a huge amount about my sweat rates and what is required during different conditions. I now have a template of my sweat rates in different conditions, which I can then refer to just prior to a race in order to accurately determine what fluid I need to maintain. As a general rule, you want to maintain no more than a 1-2% loss, as higher than this will cause a reduction in muscle contractibility/power and further than this can cause cramps, rising of body temperature and many other race ending symptoms!  Many people think that their slowing down is due to a lack of fitness, when often, it is being caused by a lack of nutrition or fluid.

The next process with finding out information about my sweat testing was a sweat analysis test. This involved doing an hour of hard training on an indoor trainer, in a lab situation. During this I had several patches attached to my arms which absorbed the sweat. These patches were then put into test tubes and sent to the AIS where they have high tech analysis machines which analyse the amount of sweat per hour and the electrolyte content of the sweat.

This was very interesting and found several things out;

  • I have a sweat rate which is on the upper edge of the normal range ~ 1L/hour of sweat
  • Very importantly I have a higher than normal sodium content of my sweat – 1.5g/hour. This value is quite high and means that I need to pay close attention to this prior to and during races, trying to replace as much as possible to avoid cramping, reduced GI function and dehydration. This means supplementing my intake during a race with extra sodium, no sports drinks have that high amount of sodium. It will also mean supplementing during the run with salt tablets in long races.

With the great help of Rebecca, I have been able to use the unfortunate race in Busselton to really learn from the experience. I now have a much better understanding of my sweat rates and sodium loss in different conditions. This is a vital element of racing well over long distances, especially in hot conditions.

How YOU can use this information:

A key for people doing any length of triathlon, especially as the time gets longer that you are out there, is to pay attention to fluid intakes. A great way to keep track and give you good and accurate information with regards to your sweat rates is:

  • Weigh yourself prior to a training session – ideally not wearing many/any clothes (ideally after going to the toilet)
  • Weigh yourself straight after training – in the same attire as before
  • Take into account
  • How much ate and drank and any toilet stops
  • Then work out your sweat rates per hour

(Difference in weight pre/post training + amount drunk/food ate) ÷ hours of exercise = Sweat rate per hour

This will then give you 2 very valuable pieces of information:

  • How much you sweat per hour (approx.)
  • How good you were in that session at replacing your fluid

You can then use this information to work out how many bottles of fluid per hour – most bottles are 700ml, that you will require in a training session and in a race.

Why should YOU pay attention to this?

  • A loss of over 2% will cause a big deterioration in performance – which is about 1.5kg for a 75kg athlete or 1kg for a 55kg athlete.
  • Many people think they are just getting tired towards the end of a longer or hot session and often notice an increase of heart rate. This can very often be attributed to inadequate fueling, rather than actual fitness. It is VITAL on race day as well as in training sessions.
  • Come race day you will be much more aware of what it takes to maintain you fluid levels in different climates and perhaps it may be the missing link to really achieving those PB’s!




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