| Theoretically it doesn't matter so long as your muscles are topped off with glycogen - aka carbo-loaded. An athlete with topped off stores can exercise 1.5-3 hours without any additional fuel. Past that point is the dreaded “bonk”.
In exercise, the intensity dictates where your body pulls energy from. In your Sprint you'll likely burn 1500 calories or more at an anaerobic pace. Only a tiny fraction of this will come from fat stores. By far and away most will come from muscle glycogen. Eating a GU 15 minutes before race start won’t help. It takes days to completely fill your muscles to capacity.
As far as eating during the event, your kidneys can only process and return 200-300 calories/hr back to your system. Eating during extreme exercise is mostly futile as blood is diverted away from your “non-essential” organs, like your stomach, to the muscles that are requiring it. The harder you exercise, the more trouble you’ll have digesting and processing what you put in possibly leading to gastro intestinal distress.
So what about longer races IE 70.3 and 140.6 (Half Iron and Iron respectively)? You must fuel during these events but again, the intensity of exercise dictates where your body pulls its fuel from. In a typical 70.3 the calorie burn is 5000+ calories and of course in an Ironman about 10000+ calories. This cannot be pulled solely from muscle glycogen although glycogen is required to break down fat stores. At aerobic paces (sub 80% Max Heart Rate), your body prefers its energy from fat. Even the thinnest athlete has 10s of thousands of calories in fat stored in their system. At lower rates of exertion, the stomach can do its job and process fuel although not optimally hence the need for a nutrition plan in these events.
So, what to eat the night before a Sprint? You really should start two nights before. Of course rice and pasta are good choices but any low fat high carbohydrate fuel finds its way to the muscles (and too much, to the belly and hips!). I also recommend sipping on sports drink during the entire day before the race (2x28oz Gatorade on my desk now for my 20 mile run tomorrow). This assures hydration and carbo-loading.
The morning of, eat light and early. Remember, once the gun goes off, the stomach shuts down. You don’t want that happening if it’s full of difficult to digest material. For this reason, I prefer Cream of Wheat made with water (not milk) with a little sugar for taste.
Good luck in your race and let us know how you do!
__________________ Scott < is |