We realise that to run a marathon in 3 hours (or 2 or 4 for that matter) will cost us a certain amount of carbohydrate stored in glycogen and a certain amount stored in fats. We top this up with carbohydrates during the run and we have more or less success (in a nutritional sense)depending on how good we are at getting the right quantity into our system at the right time. But the complicating factor is that we sweat. On a hot day we sweat a lot, on a cool day we sweat a little and on a cold day we only sweat icecubes. But our carbohydrate intake is often linked directly to our re-hydration schedule. This is because for many of us we rely on carbohydrate drinks of various forms to provide our water, salts and carbohydrates in fixed quantities. We use the same formulas for a deadly hot day when our highest priority (and most impossible task) is to replace our salts and water, as we do for a freezing cold day ,when all we really need is carbohydrates (because we’ve lost little due to sweating).
So here is a marketing angle for any aspiring sports nutrition producer. How about supplying a pre-mixed drink that comes in various temperature formulas. Ranging from highly concentrated carbohydrates for cold running to highly diluted (but still high in salts) formulas for hot runs. Maybe call one “High Sweat”, another “Medium Sweat” and the most concentrated carbohydrate model “No Sweat”.
Maybe we should just be more creative with the products we have at our disposal already, by using combinations of gels, drinks, solid fuel, and dare I say it WATER to make up the perfect solution. Of course this is just one more complication that we can probably do without, but it may be that for optimal performance we can’t stick to one fueling strategy for all conditions.
We have to remember:
The hotter it gets the more we sweat, but our carbohydrate demand doesn’t change so drastically
The colder it gets the less hydration we need but again our carbohydrate demand doesn’t change drastically.
So really all we have to do is work out a formula which tells us how many calories we need to top up per klm at a given speed and we can keep that level constant regardless of the environment. Then work out our sweat co-efficient (how much we expect to loose in attempting to cool ourselves) for a variety of temperatures and then drink accordingly throughout the race or session.