Ummm... No offense or anything, but that is extremely counter-productive to power, that which helps martial artists bust through bricks and strength which simply cannot be trained well with such a low strength exercise in the first place. Not only that, it doesn't work out your entire upper body, although it would get quite a bit I suppose. And sit-ups, if you haven't read it already, are not great for anything.
Spencer:)......
I will agree that the info about the exercise zayn provided is more than likely not the best way to build the essential power to punch through brick, but I wouldn't go as far as to say coutner-productive!
I'm sorry, but I would. And again, no disrespect or anything even though I know I sound like a D-bag. Anyways... Power is work over time. High power output is achieved with more work, less time, or both.
Not getting into the math, the more strength it requires you to do and the faster you do it, the more power you have, which is what you're looking for something like breaking a board.
Spencer.. No.

First off, you still didn't even mention why that would ever be counter-productive, which would imply that somehow it's training that actually magically reduces your strength, which is obviously not the case at all, and if you wanted to keep claiming that it is, then you really need to explain the "magically reduces" part with an actual mechanism, rather than 'not going into the math'.
Doing slower movements where the muscle fibers are fully recruited for prolonged contractions is actually quite effective at training muscle fibers, increase challenge, stimulate muscle growth and even helps hormonal and neurological adaptations (particularly recruitment of more fibers and coordinated unison contraction of them, giving you access to larger amounts of strength) that also improve strength.
If you can do an iron cross for a small fraction of a second or hold it for 20 seconds, those are quite different effort levels and training stimulations, and the longer one is actually more effective even for strength, "power" etc.
While plyometric is good and all, it's not the only type of exercise in the world that can help strength, power etc.
In fact beginners often have the problem that they launch the weights around so their muscles are actually minimally challenged and get to rest at the start and end of each fast contraction rather than getting good negatives, and the only thing that ends up getting trained is good old inertial motion...

In addition, the example of breaking a board does not necessarily require "power" or "strength", it requires training in a bunch of other unrelated areas which include proper form and trajectory, strengthening of bones through microfractures etc. And yes, explosiveness can certainly help, but you can pick-up a lot of speed with proper form and circular motions for example, and having increased mass and being able to continue to push through at impact rather than bouncing back helps too.