the way i was taught back kick was , both heels turn toward target , head turns towards target same time , picking up your back leg , chambering to chest , and thrusting backawards motion always looking at the target , the thrusting backwards motion is very similar to side kick motion ,,,, kind of exactly as joe rogan demonstrated ,,btw his technique was almost perfect ,,,,
the other video posted by kyrillo , with all due respects ,, the kicker was not looking at target at all , he was looking at the ground ,,in the opposite direction , which is recipe for a kick in the face and it is harder to finish the kick and land forward ,,,,
some tips i wouldnt mind passing to whoever want them ,,,,ive been working on a sort of plant pivot attacking back kick ,,simliar to mauy thai plant pivot round house kick ,,,,
imagine your lead leg forward ,moving forward foot to the left or right ,planting and then pivoting all the way , kicking the back kick ,,,,also bringing your lead foot back towards your other foot on an angle and then kicking , also shuffling it forward and then kicking ,,,
these types of steps prior to back kick works wonders on in close fighters ,,,, guys who like to jab ,or dance away ,,with those little steps you dont need as much distance to deliver the kick and you are also given the opportunity to lead your opponent ,,,same steps also work good for spinning hook kicks ,,,
ive been modifying these steps for myself as a defense for the better boxers and also the guys who like to rush in ,,,the only guys ive seen use these steps , would be serkan yilmaz - k1 and cyrus washington k-1 im sure there are lots of others but yilmaz is a master at the step back kick ,,,, peace out , hope this helps someone
YouTube - Serkan Yilmaz Taekwondo K1 Highlights Teriyaki Boyz Feat. Pharrell Williams - L.A.R.G.E.