There are three common ways of tenderizing meat, and they are mechanical (by using one of these tools), slow cooking, and enzymes.
Collagen and connective tissues are responsible for tough meat. At over 160F, this tissue will slowly start to turn into soft gelatin, but if you cook it too quickly, the meat itself will become dry and tough before the tissue has a chance to soften. Slow cooking means you give a chance for that gelatin to soften while not overcooking the meat.
There are molecules out there that will start to break down the meat and naturally tenderize it. There are many options out there to do this, such as salt, fruit, add an acid, or there are even man-made powders created specifically for tenderizing meat.