The day we performed this set, we had only 2 swimmers per lane, which allowed us to have very individualized intervals. We did this set in a SCM pool (our normal training location) using our SCY best times. Most of our swimmers were able to make their goal by 7-8 seconds and were able to push themselves pretty hard on short rest. This set could be used for freestyle or butterfly as well, we were just looking for some back and breast work.