I was planning to swim 4000m today. I did 100m warmup because the Masters workout was 2400m and I figured I'd do 3 X 500m after the workout. As it turns out, the workout included a good bit of speed work that toasted me pretty well. After completing just 1 X 500m I decided it would be better for me to call it a day rather than just swimming a slow, weak and sloppy 2 X 500.