OK so today was supposed to be a swimming day but it worked better schedule-wise to swim yesterday so I biked today instead.
Except yesterday after swimming laps I stayed for "Aquacycle" class, and essentially biked for an hour yesterday in the water (really, really fun). And then tomorrow is a bike/run brick.
It's not the pedaling that is a problem. It's the time spent on a bike seat. My butt still has not built up a lot of endurance for biking. Even with the new gel seat, I get sore.