My first attempt at a CSS (critical swim sped) set wasn't very successful. I couldn't keep with a 48 second length time even over 100m. I rest the timer to 50s (equivalent to 5:00 minute 200m) in a 33m pool and couldn't match that either. I think a combination of factors were at play. First, I was probably still tired from Wednesday's circuit; my abdominal muscles certainly were. Second, I felt as though I was rushing my stroke to stay on time and this was very likely making me inefficient.
I think I'll start with 50 seconds per length next week as I know that pace is attainable over short sets.