Learned?

Swimming a sprint set this morning I discovered, rather sadly if it has taken me this long, how significantly to speed up my fly – to kick my legs properly.

I managed for a shortish distance to get significantly more power from the kick. It was nice, and convincing.

I am sure that this is largely a matter first of timing. Body shape etc follows naturally from the additional impetus.
Something for Google, and lots of practice (with fins for part of the time).