while the majority of my training has been in karate, it is my belief that these principles are for the most part universal, as they deal with body mechanics in general as opposed to specific practices or techniques

Tense muscles are strong, but they are also slow and difficult to move. This is a good thing for a finished technique, as it makes it less likely for your strike to bounce off its target, and makes it harder for an opponents block to move.

Loose muscles are fast, and move freely, but they do not have a lot of strength. This works well during the execution of a technique, when the most important thing is getting from the start of it to the end as quickly and efficiently as possible.

An effective technique is one that uses the both types of muscle tension, taking advantage of their strengths, and avoiding their weaknesses. A good punch, for example is like a whip, flowing out loosely, and then snapping tight at the end.

In combinations of more than one technique, this transition between loose and tense gains a new layer to be practiced. When your muscles are already tense (i.e. at the end of a technique), they must be relaxed for the next technique. Simply relaxing the muscles works, but it takes an extra fraction of a second, and all of the energy stored in the muscles is dissapated. Releasing the tension as you begin the technique directs the energy into the movement, and makes it slightly faster.

Proper muscle tension is critical to efficient technique. Tense up too often, and you end up pushing more than striking as you work against your own body. Stay too loose and your techniques, while quick, are unlikely to penetrate. It is this fine line between bashing and slapping your opponent with a wet noodle you must walk.