In TKD we tend to test students at the higher grades doing jumping and flying destruction techniques. To do these well you need to train specifically for it. As well as a good base fitness level and muscular conditioning, particularly lower body, the method of doing this is through plyometric training incorporating short stretch shortening cycles.
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Plyometrics
Continuing on the theme of power training, essential for Taekwon do jumping and flying kicks but also generally for kicking and explosive hand attacks when sparring. Here's a video to give you some training ideas to improve this part of your armoury: