Fast twitch muscles are used in short bursts of anaerobic activity, such as short sprints and the bursts of activity used in sparring. To increase kicking speed and power, you need to develop your fast twitch muscle fibers. Specializing in aerobic training develops mitochondria in muscle fibers. Mitochondria are the oxygen cells that enable you to run extended distances. However, an increase of mitochondria cells deters the development of fast twitch muscles, which reduces the concentration of anaerobic enzymes and decreases muscle mass. Both of which we do not want to do as Taekwondo athletes since this will decrease the speed and power of our kicks. As a general rule, long distance runners have low vertical jumping ability, as kickers we want to be able to jump high.
To win a sparring match, you certainly need some aerobic training so you can maintain your energy output throughout a match, but to be able perform kicks that score, you need a lot of anaerobic training. Therefore, you should perform aerobic training for 20-minutes, 3 to 4 times per week, at approximately 70% of your maximum heart rate (220 minus your age), but then you need some intense anaerobic training.
One way to do this is with resistance training in the form of squats or lunges using high weights and few repetitions. Sparring competitors who want to last through several rounds, need to develop their local muscular endurance (LME). To do this with resistance training, use light weights and perform many repetitions, perhaps 20 to 25, to develop the ability to deliver successive kicks. In addition to resistance training, you can perform short bursts of high intensity effort on the heavy bag, run wind sprints, and, of course, perform plyometrics.