10m warmup, building the stroke  from arms only, steadily increasing rate and pressure.
 
4x6m on, 2:15 off
1st: 2m, 2m, 2m, starting at 22spm & 5K+6, up two each change
2nd: 2m, 2m, 2m, starting at 24 spm & 5k+4, up two each change
3rd & 4th:  1:30, 1:30, 3m, starting at 24 spm & 5K+4, up two each change