Yikes, that was a difficult swim workout. I warmed up, drilled, and did a few hard 50s to get the heart going, then I hopped in the SwimEx for my long, continuous swim. Last week I swam 20 minutes; this week I swam 24. And I swear I could tell when 20 minutes had passed, because I felt sooooo tired.
I'm hoping that it's just because I lifted yesterday morning, and my arms are tired from that. Otherwise, I'm going to have to reconsider increasing my volume by 20% every week.