New rodeo is out; check it out. Lots of fun stuff.
I think we got the Pro MMA Radio link fixed. Go over to the banner on the right and click on it to listen to the show while you read my post! It's my absolute favorite source for MMA information, both entertaining and informative.
I was reading a book the other day (Bone Crossed by Patricia Briggs). It's an urban fantasy novel, not a martial arts based book. The main character happens to train in karate (again, not a major theme of the book) and is taking a class. The instructor has the class warm up, spar, and finish up by doing 300 side kicks out of horse stance - per leg. 300. The character (the book is a first person narrative) thinks that for the better, more focused students, the 300th kick looks just like the first one, but that she's too tired to manage that.
You know what it means if you can do 300 kicks in a row and have the 300th kick look like first one? It menas your kicks suck. Sorry to break it to you, but it's true.
A really great kick is very fast, very sharp, and very snappy. Why? Because kicks are meant to damage your opponent. A slow kick, even if your weight is behind it, might push your opponent away (which might be your intent sometimes), but won't do as much damage as a faster kick, even if the faster kick has less weight behind it. Think of this analogy - would you rather be hit by a train going 1 mph or a baseball going 100 mph? The train has more momentum and more kinetic energy, but I think we all know all the train would do is knock you back a step, while the baseball might kill you. The greater the difference in speeds at collision the greater the energy transfer will be.
So you want your kicks to be snappy. That means you want to use fast twitch muscle fibers, and a lot of them. Fast twitch fibers are the ones that produce the most force in the shortest time. They're also quick to fatigue.
If you can do 300 kicks at the same pace you're not using most of your fast twitch fibers to do the first kick. If you were, they'd be exhausted early in the session and your kicks would be slowing down considerably. So to maintain a near constant pace you have to either have trained your legs to be mostly slow twitch fiber or you are only utilizing a small percentage of the fibers for any one kick, giving the majority of fibers time to recover as you cycle through them.
Which means that your kicks suck. Or at least they suck compared to what you would be capable of if you trained properly.
If you train to throw 300 straight kicks your body will adapt - it will change your leg fibers to slow twitch fibers and your nervous system will "learn" not to use too much muscle at once or move too fast. You'll get good at doing long sessions of kicking. But your first kick won't get faster or stronger - it will get slower and weaker because your body is learning to conserve energy.
How do we get kicks (or any technique) that don't suck? When you practice anything practice it at absolute maximum speed and power. Then stop before you get too tired. Convince your body that it needs to be quicker and stronger, not last longer. Do 10 kicks per leg, or 20, taking nice deep breaths and resting as much as you want between kicks or legs. Ideally, throw a few kicks per leg, over a few different kicks, all at full power, and repeat this several times each day. Never, or rarely, kick when tired or slow.
How do you get in shape, then, if your kicking (and punching) sessions are too brief to challenge your cardiovascular capacity? I'm glad you asked. By all means do some high intensity interval training, but do it at the end of your workout and use non-karate movements. Do burpees, power snatches, sprints, squat thrusts, or swings for your conditioning. That way you'll develop mitochondrial capacity in your leg muscles and the heart and lung adaptions you need without messing up your skills.
I practice kicks and punches daily in my office, throwing 4-12 punches and 8-20 kicks at a time (which probably takes a minute or less). A couple of times a week I head to the gym and do a bunch of kata (which I can't do in my office) and finish the workout with burpees. That's how you stay fast (or, for me, relatively fast - I'm still slow, just faster than I used to be) and keep in shape enough that you don't fade during long classes, sparring sessions, or promotions.