I read this workout on The Holistic Triathlete and I think I’m going to add it to my training plan once I’m ready to add another tough swim.
Obviously I still don’t understand all the warm up terminology, but the main set is quite simple:
20 x 100 threshold pace*. This should be a pace that is hard to hold over the course of the 20 x 100.
Swim off a fixed interval, giving you 10-15 seconds rest, e.g.:
If you hold 1:10s per 100, your interval should be 1:20/25
If you hold 2:00 per 100, your interval should be 2:10/15
I’m at the 2:00 end of the spectrum for 100m (actually probably about 1:45 for this exercise, which makes it even easier – 20 x 100 at 1:45, setting off every 2 minutes). It feels like a monster, but it’s these kind of sets that will allow me to go quicker over 10 miles…
1000kmstowindermere 
When I was training for my 1/2 Ironman, I did many swim sessions like this. I even did some 30 x 100. It really helped alot. The hardest part for me was wrapping my head around doing 20-30 sets. To me that was very overwhelming.
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