Advice: 90 Min OTB Fatigue

You should work out physically more. Maybe try hitting the gym every now and then?

Also, eat well before your match, rest after eating for at least 30 minutes and drink a lot of water.

I generally drink a soda or two when I'm playing at a shorter G60-G90 event at my local chess club. But when I travel to tournaments such as those at Vegas or St. Louis, or play in the Chicago open or supernationals, I also avoid caffeine.

Yes, wafflemaster has some good tips. I have experienced caffeine crashes in tournament chess before so I try to avoid it. You shouldn't overeat as this seems to lessen blood flow to the brain. If you're hungry, eat just a little bit, not too much.

I for one don't hit the gym (although I may walk around, wash my face), but simply have a willingness to play usually. If I know I have to win, I'll be likely to forget about my tiredness and just continue looking for good moves out of habit. I think state of mind counts for a lot. If you are continually amused by all of the thinking that occurs in a chess game, you should have enough will to keep going. You have to understand that when you play these types of games you are in for a long fight; embrace it!

I've gotten away without a good night's sleep, but it does help.

If time controls aren't an issue for you ...I would take more occasional breaks during the game walk around get the blood flowing....

i heard caffeine is bad for your nervous system anyway but that might be a myth

Let me tell you that is not true. Both of the tourneys I've been to had 2 games a day.

I don't have much experience of this sort of thing in chess but I have played many bridge tournaments requiring concentration over the same sort of periods. What I tend to rely on is my bridge autopilot. An autopilot is not so effective in chess but nevertheless I think you can conserve your ability to concentrate by taking things a bit easier some of the time - the earliest moves in the opening, say, or games against players either well below your own standard or well above it. Save intense concentration for the early middle games and tough endgames.

Another tip is to try to have some interest going that is not chess. Play some kitchen bridge between games, or follow the fortunes of your favourite football team or chat up that nice looking waitress in the coffee shop opposite the venue.

Not coffee sleep alot of it and exercise it's like running a marathon if you want to go the distance you need to be in physical shape and have the energy for it otherwise your not going to make it.

Eat lots of fruits and veggies, whole grains with low gi, lots of fish and nuts, eggs protein, beans, fresh garlic, salads it's all good.

When I was in this one tournament, I hadn't slept for three days. Luckily there was a water fountain in the playing hall that kept me awake. Just drink lots of fluids DURING the game.

Well...

Although I had a regular workday, I ate well before the game.  I took ten minutes to put my head down right before the game...

During the game I took a stroll every 10 minutes and drank water and a buddy of mine brought me a five hour energy after reading this thread.

Thanks David!

Thanks to all who posted.  Really great advice.

Is there anywehre on this site I can play 90min tournament games??

I was playing in a tournament in Alabama several years ago and my opponent for some unknown reason disappeared and after awhile he came back to the table soaking wet.  It was pouring down rain outside and he decided to walk around in it for awhile.  Whatever it take I guess.