Workout

Warm-up (600)
400 swim
200 kick

Set (600)
2 rounds
4 x 50 RI = 10s  
...1-Fast/Easy 
...2-E/F, 3-F, 4-E
100 build on 1:30

Set (2000)
16 x 50 on RI = 10s...every 4th 50 FAST (flat out!)
...rest 1 min.
12 x 50 on RI = 15s  every 3rd 50 FAST
...rest 2 min. 
8 x 50 on RI = 20s  every 2nd 50 FAST!
...rest 3 min.
4 x 50 on RI = 30s  ALL FAST

Cool-down (200)
200 EZ