I am being monitored while on the treadmill, so it is interesting to have so many data points for my oxygen levels besides the usual blood pressure heart rate. Sitting around at night I have high 90s, sitting immediately after exercise I have 94, but at a certain exercise intensity, my oxygen drops below 88. They have a good oximeter that tells them when they are getting a good reading. I have tried usual good breathing technique but that does not bring it up. So they lower intensity. It has happened twice now, so next time I will slow speed and increase grade to see what happens. But I didn't feel any differently at the time. And I don't plan on doing any heavy work ever!