I should probably be asking a doctor on this, but . . .
Yesterday's sprint triathlon went about like every one I've done: get out of the water in the middle of the pack, blow past most of my wave on the bike, and then watch them all pass me on the run. Mostly as I'm walking for decent stints because the pain in my knees is so bad I'm going to cry (probably because I weigh 230, and never do any real run training, because the pain in my knees is so bad I'm going to cry). And my ankles hurt, too. No past or known present injuries; I'm just a big guy who doesn't like to -- and thus never -- runs.
Is this something where, if I suck it up and run some miles over a few weeks, I'll build up some tolerance? 'Cause I'm sick of making it two-thirds of the way through the race in good shape and a good place, and then falling apart when I still have plenty of cardiovascular capacity but my leg joints feel like they've been hit with a hammer. If pushing through the pain in training will make it go away for further training and events, I'll do it. Otherwise, I'll stick with bike racing.