This was the crowd-pleaser of the week for the Masters team that Barbara coaches. The set, which is a "take it to failure" set, can be swum as all freestyle, but it also lends itself to variation.
Swim at least 5 rounds of the following, tightening the sendoff on the 100s until you can no longer make the sendoff. You can do any stroke or combination of strokes on the 50s, so long as you stick to a sendoff that gives 8 to 10 seconds rest. The 100s are freestyle (except that we had a couple of swimmers who did IM on the first 100 and freestyle on the second 100 of each round).
2 X 50 on a sendoff that gives 8 to 10 seconds rest. This sendoff will not change.
2 X 100, start on a sendoff that gives approximately 20 seconds rest, then drop this sendoff by :05 each round until you can no longer make the sendoff. Ideally, you’ll make at least 5 rounds (maybe 6 or 7).
An example of the set might be: Swim the 50s as freestyle on a 50-second sendoff; start the 100s on a 1:50 sendoff, then tighten the sendoff to 1:45… 1:40… 1:35… 1:30… and possibly 1:25.