Most dojos you find will have at least one heavy bag, either dangling from a chain from the celing, or wrapped around a pillar, or weighted to the floor, something like that. I've never seen anywhere with layers of sponge though, has anyone been fortunate enough to find something like that? I've kicked under water before, that's about the only thing you can get for enhanced resistance I think, since filling a swimming pool with gelatin or whatever for these purposes would be just too expensive. Sponge makes sense though, since they fill pits with that when they practise flips for gymnastics and stuff.As far as strength is concerned, the specific strength for a kicker is the strength that lets one pack a wallop in a kick, not to hold up a leg! Specific strength for kicking is developed by kicking a heavy bag, kicking into layers of sponge, kicking with bungee cords attached to legs and doing other dynamic exercises similar to kicking.
Bungee cords would be tough since you need to mount them correctly on the foot and hip (or further up?) to make sure it mirrored the force properly and didn't injure you anywhere. You see that stuff more often for boxing where they wear a backpack with cords coming out of it with handles you grasp onto, but grasping isn't an option for the feet. Is there anything progressive that can be trusted for this?
Even when training with resistance like stretch cords, speed is a variable, so in any case, it would be nice to have a machine (either computer or human controlled) that could measure the velocity, with and without resitance (or with various levels) to measure progress in that way.
Even though training with dynamic is most important, I think static-active is a good thing to train (so long as it doesn't injure, you need strong back muscles as he says) since it builds force production in extreme ranges of muscle shortening which tend to become weak due to over-active insufficiency. Training like that, maybe it overcomes that, or recruits muscles we don't use as much which are not as short so they can generate power. Who knows...
But anyway, one thing I thought about for static-active, along the lines of a partner applying resistance that they take away for "pink panther" or whatever... what about doing it standing on your toes?
Basically, you do the active stretch, and then while maintaining it, slowly rise up onto the toes (ball of the foot) of the base leg. Then, quickly, you drop it down. The first thing to drop would be the leg and the hips, and then the raised leg after that... but what if it did not drop as much? It would already be 'up there' or something, so maybe it'd stay, just a little bit. It's sort of like how you can pull your leg up further using your hands, and then slowly remove assistance from the hands, and tell your leg to keep itself up there longer, or at least slow the descent with control, like an eccentric or something.
