Over the last 5 days I've swum 3 times to do the week 5 tasks. That's been quite hard work especially with 2 short running days and some late nights on the computer doing work. By today's swim I was physically tired and it showed.
Today's plan session was easy/medium/hard blocks but these have lengthened to 100m. All in all I swam 2300m (2nd record this week) which might also explain why my pace was slower then 2 weeks ago for each interval. I also notes quite a drop off in pace between the 4 sets, another indicator of fatigue.
I really am in a position now where I can use my arms aerobically as this week's sessions have all been around 1 hour with a set of up to 13 minutes.