He actually has a super strange technique. See here: www.reddit.com/r/Sprinting/comments/f3ruq0/shuhei_tada_block_starts/ for a up-close vid and some analysis by a few coaches in the comments. He is very hunched and broken at the waist, toe drags the first two steps, then cycles with high heel recovery immediately. But despite these 'wrong'/unorthodox things he does, his start works for him, he is super quick at the start of the race.
