Last week as part of the warm-up we did the following set:
4 on 45 seconds
8 on 40 seconds
4 on 35 seconds
The first 12 allow you to build to a stronger pace with a challenging finish to the warmup. You should be ready to swim fast after this set!
Adjust the times to suit your pace so you can cruise the first 4, have 3-5 seconds for the next 8 and then have to push it to hit the interval on the final 4.
For example, if you hold 60 seconds for 50′s on longer sets, your intervals might look like:
4 on 70 seconds
8 on 65 seconds
4 on 60 seconds
Try it and assess how it goes. You can adjust the intervals up or down to ensure it is doable but with the need to swim fast to hit the final 4.
Let me know how it goes!