As an aside to the strain on joints, in my 2nd year of training (still fairly clueless) I was doing punch outs drills with 5 lb weights, trying to build strength and speed. What I mostly gained, was a hurt lower back from the strain that took the better part of another 2 years to recover from. Even today I still find myself more susceptible to lower back injuries.

There aren't too many short cuts to speed and power. I've learned it is a process of developing the body, and all of it, not just a few specified areas with a few specified drills. Trying to work something like this drill, without a properly built up core, strong legs and upper body ready for the stress it may apply, is nothing short of a recipe for disaster.