Improving swimming is all about sustainable changes ! I see so many athletes going to swim clinics and getting advice from coaches to change 5 to 6 things, to do impossible drills and only getting confused. They look great for 50m but it's not a sustainable change they can hold for the length of their races so it's pretty much useless. After this session, I asked the athlete, the very next day to do, 40 x 50m with 10s rest using same stroke and she did ALL 50's in 56-58s (easy effort), a REAL 24s/100m improvement ! That's what I call sustainable change!