Well after my competitive days were over, I tried the bicarbonate ingestion as an experiment. I swallowed the stuff, waited a couple of minutes, and got on an elevator (I was staying in a hotel) to go out for some hard running.
When I reached the lobby, I hesitated to start the run because I felt an odd queasiness in the lower abdomen. I decided to go back to the hotel room, just to make sure there would not be digestion problems to contend with during my experimental run.
No sooner did I make it to my room than an overwhelming need to hit the bathroom swept through me like tidal wave. It was diarhea like I never had before or since in my life.
It was scary. I lost so much fluid in my body that I was thirsty for a week. For me, at least, bicarbonate would seem to be an utter disaster.