Monday 2 June 2008

Weight loss test

I did my last long run on Saturday (I'll blog about that tomorrow with the usual stats) and decided to use it as my weight loss test for the WHWR. The temperature was >20C and very humid. You could feel the water literally rising from the ground from the last week or so of pretty sodden, but warm, weather.

I ran 19.2 miles with ~1400' of ascent and descent at an average pace of 9:17 mins / mile and knew from the start it would be a very sweaty affair, probably more sweaty than the WHWR will be by far. The run took me 02:57:33 to complete.

Starting weight = 64.6 kg
Inputs = 1.2 kg (1l water + 1 clif bar + 1 go gel + 1 high 5 gel)
Starting weight + inputs = 65.8 kg

Finishing weight = 62.7 kg
Total weight loss = 3.1kg
As a % of starting weight = 4.8%

Quite amazing to have lost 3.1 kg in just under 3 hours, and something that shows how much can be sweated out in hot, humid conditions.

I lost more than the +/- 4% of body weight recommended by the WHWR Director and Doctor but I am not concerned. In the race I will definitely take on more water than 1l over 3 hours in these kinds of conditions, and it is unlikely to be as consistently hot or humid. But at least the run has given me some data to use as a baseline.
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4 comments:

Phil Robertson said...

Hi Brian

I took so much stick from friends and family after carrying out this test! Important though.

I've carried the test out in cold conditions, warm conditions, hilly runs, flat runs etc and my sweat loss rate nearly always seems to be 1 liter/hour (very similar to yours).

You're right, it's an amazing amount of weight to lose.

Cheers for the 'tag' I'll look again at it and respond. Not sure who I'll tag though - does it have to be a WHWer??

Phil

2 June 2008 at 21:01
Thomas said...

Brian,
you are raising an important point. Your little (self-)study does show that it does not require a large effort to simulate conditions for a considerable weight loss. If you add other causes of weight loss eg emptying your bowels and bladder, change of gear etc you can expect an even higher loss. You also have to add perfectly normal weight loss caused by carbohydrate depletion in particular of the upper leg muscels which can be as much as 2kg and more. But still be in a perfectly healthy state. However looking at the medical advise of the WHWRace officials you might be put aside and wait for further medical checks. I do find this quite concerning.

2 June 2008 at 23:13
Brian Mc said...

Hi Thomas - I contacted the race doctor directly to ask whether I should be concerned. Given that the race temp and humidity will almost certainly be lower, that I will be running more slowly, that I will be drinking more than 1l over 3 hrs (probably around 500mls per hr), that my body coped with the 4.8% weight loss and that I have now run 9 ultras and never suffered from dehydration or overhydration, he confirmed I shouldn't be particularly concerned. He will be following my weight changes (as with all runners) and I will clearly need to monitor my fluid intake but I am not worried.

3 June 2008 at 08:29
Thomas said...

Hi Brian, if you are not worried then I should not be worried too.
It's just pre-race panic which starts to grab me. I usually gain weight rather than loosing so I'll be fine.

3 June 2008 at 16:50

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