Well, Opinionated Alchy, everyone skimmed right by Jim--except you. As it happens--you're both right. It IS baking SODA--I should know. I worked with a superior chef from Taiwan for several years, and to this day haven't found a restaurant that could touch his food. As you point out, OA, it can be a combination of things--it all depends on what you are making, and how tough the cut of meat is. But if you do nothing else, baking soda will break meat down the fastest. Soy sauce also works well, but takes a bit longer. (Not too much--if you leave steak chunks overnight in a marinade of it, you will see what I mean.)
It's amazing how the guy most ignored (Jim) and the Alton-ish alchemist turn out to be right...while the whole band played on in just the wrong key. Folks need to learn to listen to those they are inclined to ignore a lot more often. They just MIGHT learn a thing or three.
Just sayin'. ;-)