A long ride on the trainer.

After the warm up, the workout called for four 30 minute sessions stair stepping from 159 watts 195 watts.

The first three sessions went well. I could ride at the requested effort easily. The same is not true for the fourth session. As soon as I started it, I knew I was in trouble. After ten minutes, I had to take a break, so I stood which means I can only peddle with one leg at a time (because of the power cranks). After the short break, I could not maintain the required effort. After five minutes, I realize that the cause was lost and I got off of the bike.