Q&A with Lyle McDonald, author of The Protein Book
Some coaches tell their sprinters not to each too much carbs the night before a race, as the theory is 1 gram of carbohydrates requires 2 grams of water to store as glycogen. The end result may make the athlete feel “bloated”. On the contrary, for an endurance athlete, carbs are a great fuel source and the stored water is an extra bonus. What are your thoughts on this for sprinters?
A: Lyle McDonald:
I think the coaches are mostly right in this case, certainly in the case of sprinting. Glycogen levels shouldn’t ever be limiting for a sprinter, the glycogen depletion just isn’t there. Even a 400m guy who has to run heats shouldn’t run into problems unless he’s on a zero carb diet the entire week before. Basal glycogen levels should be plenty to get through any competition I can think of and the stiffness and extra weight gain that occurs with carb-loading is as likely to hurt performance as anything else.
However, for endurance athletes it can be a bit more complicated depending on the sport, the specifics of the event and the distance involved. All of this goes into determining whether any benefit from hyper-hydration and carb loading outweighs the potential negatives of carrying extra weight. Some of the considerations work looking at appear below:
For something like cycling and things of that ilk where body weight is supported, gains in body weight are probably cancelled out by not bonking and going into it more hydrated should help. This might not hold for events where there is a lot of climbing involved (where even small gains in weight make a huge difference in energy cost); as well cyclists usually don’t have major problems eating during their event so in that situation (a race with a lot of vertical ascent), coming in a bit lighter but maintaining glycogen stores by proper on-bike feeding might be the superior strategy compared to carb-loading and having to carry several extra pounds up the mountain. Fluids can be consumed easily on-bike as well. For a flatter race or longer time-trial, where hills aren’t an issue and eating might be more problematic (since there isn’t any time to rest and refuel), glycogen loading might be superior. Again, it also depends on the length of the event. A 10 km time trial is over long-before carbs become limiting, a 40 km time trial is right about an hour.
For running where the entire body is being propelled against gravity, the extra weight gain might be a hindrance. This has to be weighed against the length of the event. Normal glycogen stores can get an endurance athlete through a good 60 minutes of competition even up to maybe 90 minutes, especially if they can consume even small amounts of carbs and fluids during training. When you get to events like the marathon, that’s where things become problematic. The best marathon time is about 2 hours and that’s beyond normal glycogen stores can support. Compared to cycling (where eating on the bike is usually easily accomplished) eating and drinking during a run can be more difficult, some runners get stomach upset from food/liquid jostling in their gut and a contrary researcher named Tim Noakes has argued that better runners drink less, allowing them to compensate for fatigue during the event with a reduced body weight towards the end; clearly this should be tested in training if it’s even considered as a viable strategy. For slower runners, glycogen loading should probably be mandatory although, I’d note, their slower pace should make it easier for them to eat and drink.
I imagine other sports have similar issues to consider, I don’t honestly know enough about cross-country skiing to comment competently on it but most swimming events are short enough that I doubt glycogen loading would help; but since body weight is supported, I don’t know how much a slight weight gain would hurt (unless it hurts aquadynamics).