I have been swimming with a Masters swimming program for a couple of years. The workouts often include sets at various efforts. For example a set could be 1x50 easy (EZ), followed by 1x50 medium (MD), followed by 1x50 hard (HD). A more precise definition would be to use intervals or send-offs. For example 4x100 in 2:00 on 2:30, would mean to swim each 100 in 2 minutes, take 30 seconds rest and repeat. Another more precise definition would be target heart rate for a set.
When working with different coaches, swimmers would often be broken up into groups, with the strongest swimmers possibly going on 1:30 for a set, while the slower swimmers would go at 2:30.
My workout today included 150 yard repeats going 50 EZ, 50 MD, 50 HD followed by 50 HD, 50 EZ, 50 MD, followed by 50 MD, 50 HD, 50 EZ. I did 9x150 rotating through the sequences three times. Going EZ-MD-HD gave me a real opportunity to try to step it up and effectively do a descending set. It will be interesting to review my splits. The HD-EZ-MD was the most challenging as I had a hard pace in mind, but had to swim another 100 yards after that. I felt really winded for the middle 50 but proved to myself that I could recover. The MD-HD-EZ was not too bad. I could step up for the middle 50 and then get my breath back on the last 50.
I am a big fan of electronic gadgets and have been considering a Finis Aqua Pulse heart rate monitor. The device records heart rate from the ear lobe and transmits the reading via bone conduction (similar to the SwiMP3). I have held off because I have been discouraged by the true benefit I have received from the Finis Swimsense and Finis Hydro Tracker. These are fun toys that work well, but are hard to quantify the impact on my swimming. I still tend to use the pace clock and count laps in my head. In the open water, I still swim based on the land to land measurements. The Aqua Pulse could help me learn paces, but that could just as easily be done based on Relative Perceived Exertion (RPE).