Robert Lee said:If you are kicking air with non power kicking But speed and controled kicks where you do not over flex the knee Yes you may not injure it. But power kicks in the air over extend it and make it weaker and weaker over time. I dont know of any past instructors From years past that did not develop knees problems. As back when I started training that was 34 years ago. Most schools punched and kicked hard in the open air. It was not smart. I have known several that had problems later with both knees. It took me about 7 years to have to have surgury on my knee. And since then have trained much smarter no more full power kicks in the air. And do not instruct useing any power kicking other then shield and bag work. AND have had less knee problems and NO students with knee injurys from kicking.
I agree with your statement. Repetitive kicking for strength training is not power kicking. We do those on the bags or shields too. Our instructor does make black belts demonstrate kicks in the air for testing so therefore they have to practice it that way. Not good. I stopped doing those too a long time ago. Too risky to do a jump 360 spin heel, round, side, etc. in the air over and over. After ten of those, it is risking another joint dislocation. TW