Let’s not over-complicate this one. Don’t dally over the warm-up. Main set is good, strong & steady aerobic hundreds followed by one fast effort. Rinse and repeat, keeping your pacing steady and teaching your body to handle the stress & lactate.
20 x 50:
4 x swim
4 x kick
4 x drill
4 x IM order (25 drill + 25 swim)
4 x build each 50 to fast
30 x 100 as:
3 x (9 x 100 @ 10 secs rest; 1 min rest; 1 x 100 fast; 1 min rest)
Swim down: 100 strong + 100 medium + 100 easy + + 100 pull + 100 slow and relaxed*
Total: 4,500 meters
* warm downs should start pretty soon after the hard effort has finished and should descend from fast pace to slow pace. It helps recovery much better than swimming easy for short distances.