My classes were 60-90 minutes. I usually did 60 mins, longer classes did take too much out of me.
It did not slow my loss but it did not accelerate either. It is really important to add the extra calories for these classes. As mentioned, I did this for over a year prior to IP so I was very accustom to the class, heat, activity level.
Also, my coach supported this exercise on P1.
Began IP 2/13/2013
Reached 154 lbs June 2013-phased off for summer and gained 9 lbs. 10/28/13- reboot 1 (163 lbs) for 4 weeks at 159. 1/6/2014- Reboot 2 10/12/2014 gained weight need to lose it again!