I think the appropriate question is "how do I maintain cognitive function over long periods of stress?" Few shooters are actually stressing their metabolic systems so much that they are physically exhausted by the end of a 12-hour match day. But as they become psychologically tired, the body responds as it is in the habit of doing.
A decent base level of physical fitness will help but everyone knows an exception to this rule. I'd train balance, core strength, and cardiovascular system in addition to dry-firing, etc. Training for those long days so you are not surprised by a decline in performance will also help. How? Do more long days. And train in the temperature and humidity that you will compete in (if at all possible). Go early to the big match so you get over the jetlag and get used to the temps - expect three days or so to achieve some temperature adaptation. Longer if you are going from sea level to the Mile High area.
But I agree with Brian, hydration, diet, rest and recovery. Those guys aren't wearing and using hydration bladders (CamelBak) because they look cool. Drink water at the rate you are losing it - it's simple. Constant intake of small amounts is the rule. On hot days you can put ice in the bladder, test results (US Olympic cycling team 1996) show improved physical performance from the cooling effect of the cold bag on the spine (some important pulse points there). Gatorade? Stay away from supermarket drinks that contain sucrose as the sugar component. Sports hydration drinks with glucose polymers (maltodextrin) as the "sugar" component are better tolerated by the stomach, especially when it is quite hot, and the long-chain sugars burn slowly, which helps prevent the blood glucose spike (sugar rush) and certain crash that follows. Most sucrose-based drinks have a strong flavor (which is why one poster mentioned adding water to it). It's easy to get sick of that flavor and to limit intake because of it - a sure way to get dehydrated.
Eat for what you are doing. Eat for preparation, eat for movement, eat for recovery. Sears' book is a fine starting point if you want to familiarize yourself with a 40-30-30 diet. Not the best diet for hardcore physical activity but quite useful for shooting sports (based on my own experience). Eat a little, often. This robs less blood from other systems (circulation, respiration) for the digestive process, and you'll feel lighter ...
Besides diet there are some useful supplements available. Caffiene is ok especially if you do not over-respond to it. Useful for mobilizing fat as an energy source too. The "Goo" BE is talking about has the equivalent of 1/4 of a cup of coffee (who's coffee?) for each 100 calories. And it is true, if "eaten" with the appropriate amount of water to create a 4 to 8% glucose solution it will empty from the stomach in minutes (less than ten) and shoot across the intestinal wall, ready to be used. That's not true though if you ate a cheeseburger just before you Goo-ed up.
Rest and recovery, not just a good night's sleep. If you are not shooting you should be recovering from shooting and preparing to shoot again, which means resting your brain. Why spend energy on how the other guy is doing? You are effectively giving that energy to him, depriving yourself of same. Do only what is necessary. Make picking up brass your meditation. Pretend your range bag is massaging your shoulder instead of driving you into the dirt, and carry less in the bag. Wear a hat. Seek shade. Sit. Close your eyes. Relax. No one can stay "up" all day without some consequence.
Ok, time to rest and recover.
Smooth is fast,
WFMFT
(Edited by wfmft at 8:45 pm on Mar. 5, 2003)
(Edited by wfmft at 8:50 pm on Mar. 5, 2003)