During exercise your body produces hormones that reduce the need to pee (part of the old ‘fight or flight’ response). You’re also likely to be sweating a lot, which again reduces the need to urinate to conserve body fluid. So if you end up peeing a lot during a half or full Ironman, you’re likely drinking too much and might benefit from backing off the fluid intake a touch.
In terms of what constitutes peeing ‘a lot’, I usually tell athletes it’s not a bad thing to pee once on the bike in a half-distance event, possibly twice in an Ironman. This tends to show that you’re drinking a reasonable amount but not massively overdoing it. Much more than that and I’d say it’s a sign of either taking in too much fluid, or insufficient sodium within that fluid to retain it in your body.
Sodium is crucial for maintaining fluid balance,and also plays an important role in the absorption of nutrients in the gut, maintaining cognitive function, nerve impulse transmission and in muscle contraction.
If you don’t pee at all that’s not always a big problem, but it could also show that you’re becoming more dehydrated than is optimal for a good performance, so consider slightly increasing fluid intake.
Whatever you do be careful how and when you pee during a race – while many do pee while riding the bike it’s actually against race rules, and can result in a yellow card or stop-and-go penalty if seen by a race referee.
Andy Blow has a few top 10 Ironman and 70.3 finishes and an Xterra World Age Group title to his name. He founded Precision Hydration to help athletes solve their hydration issues. He has a degree in Sport and Exercise Science and was once the Team Sports Scientist for Benetton and Renault F1 teams.