trs96813,
When performing PR sessions, it's best to keep to 30 minute intervals. During the first three 30 minute intervals ... you take a short break of 5 minutes between intervals.
After 90 minutes however, you lengthen your break between the 30 minute intervals to 15 minutes.
So ..
Session one - 30 min with 5 min break.
Session two - 30 min with 5 min break.
Session three - 30 min with 5 min break.
Session Four - 30 min with 15 min break
Session Five - 30 min with 15 min break.
etc... etc ...
It was found that PR'ing or learning in this fashion was optimal.
Again, read your body signals ... if your body say's 'hey I need a break' ... listen and do it. You won't tire as easily.
Our mind and bodies are connected to form a complicated 'machine' ... too much work and you could be heading for a breakdown, so to say .. so break every so often to allow the 'machine' to recouperate.
Michael Saikali