Originally Posted by spingineer
This is a dumb question ... but doesn't caffeine dehydrate you? Also, coffee makes me go to the bathroom, and makes me go pee almost immediately after starting the ride.
Coffee is really not that much of a diuretic as people think. Do a test where you drink 2-3 cups of water within an hour and sit around and see what kind of peeing you get. It's the excess liquid you're taking in that causes the peeing, and to a lesser extent, the caffeine itself.
However, when you're exercising and your water-intake requirements goes up, the water from energy-drinks or coffee is used to replace that which you sweat away and the kidneys never extract that water as excess. So if you start riding right after the coffee, you won't have any additional need for pitstops.
But the actual glycogen-sparing effect really isn't that big a deal really. I'll bonk in about 3-hours or 50-60 miles without eating. With caffeine, I might make it an additional 10-miles, not that significant. Regular ingestion of energy-drinks and food will extend your endurance much, much further than caffeine. However, if you're doing an event where you're limited in the amount of food you can eat, or if eating upsets your stomach (like running a marathon), then yes, that little extra bit of distance might be covered by the caffeine.
Another effect I've notice that wasn't discussed is pain-tolerance. Being a stimulant, it increases levels of adrenaline and epinephrine in the body. These lessens the sensations of pain in the brain. This will help stamina as you won't be feeling as much hurt for the same efforts, such as riding at LT in a TT. When doing sprints & intervals, I find that the pain-masking actually helps me push for that extra couple of seconds before quitting.