Oct 272015
 
Nutrition for a 100 miler

Salt – do we really need it ?

The ability to measure our sodium losses in sweat during exercise has led some to thinking that we need to replace at least some of what we lose in sweat to ensure our blood sodium levels don’t fall to levels that effect performance or health.

The thinking goes that somewhere between 230-1700mg of sodium can be lost per hour during exercise in hot conditions and we have a typical daily intake of 4g. As a consequence it can take only 2-3 hours before we deplete our sodium stores levels that effect performance. But measuring sweat sodium levels is only part of the picture – our body doesn’t particularly care what our sweat sodium concentration is (and in fact it reduces sweat sodium concentration as it acclimatises to exercising in the heat). What the body very tightly controls is our blood sodium levels and has several mechanisms to keep it within 135-145 mmol/litre range that is required for normal human function.

One thing to understand is its not the actual amount of sodium in our body that is the critical factor, its the concentration of sodium in our blood. If there is less blood then we need less sodium to keep the concentration in normal range.

Deciding we need sodium supplementation based solely on what we sweat out is like basing fat consumption based purely on how much fat we burn during exercise or basing our hydration strategy purely on how much weight we lose or our carb intake on how much energy we burn when we run. What we burn or sweat out doesn’t matter – its whats left in the body that we need to be concerned about. So when we look at fat burnt during exercise we know that we have ample supplies of fat so there is no need to take on additional fat, we know that our carb supplies will eventually run out so we need to take in additional carbs in a race but we know we don’t have to replace the whole amount we burn, we also know that the body can handle a certain level of dehydration with no adverse effects provided we drink to thirst. As far as sodium goes what we should be looking at is what happens to our blood sodium levels during exercise NOT how much sodium we lose in sweat.

Do we need to replace all of our sodium sweat losses, some of them or none of them?

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Apr 242013
 

Photo - Hoka One One Australia Facebook PageCramp. It’s a runner’s worst nightmare. One minute you are running along feeling great, next minute you are clutching your leg trying to find a way to relieve the cramp that has taken hold of  your calf or hamstring. If this happened at the finish line it wouldn’t be such a problem, but when it happens with 30k or more to go it becomes a big problem. I have either been lucky or well trained as it has never affected me in a race. But when I talk to other runners i realise it is a very common problem and there are a lot of different ideas as to the causes and remedies for it. Some of these have  been shown to be scientifically incorrect. There is however one theory which seems to fit the evidence and we can use this, combined with some common findings on who suffers cramp, to outline some prevention strategies and  remedies if cramp strikes. Continue reading »