Yesterday's circuit was uneventful and felt considerably less onerous having not done a long Tuesday run nor a Wednesday swim. My morning resting heart rate is reflecting this by being below 45bpm.
This afternoon I took a few hours off work and did a swim routine with warmup, fin sets and then 4x 400m sets before a few cool down lengths. This came to a total of 2100m which is a record. I was in the water or more than an hour so it wasn't rapid. In the first three sets I easily achieved under a minute per length but by the fourth I wasn't able to. I knew I was tiring and my form was failing so I did consciously focus on going a little more steadily whilst trying to keep a leading arm and front quadrant technique. Notably as the pace dropped the strokes per length increased which to me suggests a clear lack of power and 'catch'.
I think one of the most important aspects is that I was moving for just over an hour and coped with waves breaking over me from faster swimmers. Basically over the last few months I've become stronger and more reliable if not especially faster per 100m.