I have trained using the uphill athlete program for around 3 years and I am also a BJJ Brown belt and train BJJ 3-4 times per week.
BJJ is a great workout but it’s defiantly on the higher intensity, muscular endurance side of training. Scott is correct that it does not translate well to performing well in the mountains but I have found that training for the mountains and expanding aerobic capacity greatly benefits BJJ. The times when I’m in my best uphill shape I can roll for hours without getting tired.
The key for me has been to not let BJJ workouts take the place of any of my aerobic workouts, it’s just something you have to add in extra. It depends on what my current training objectives are, if I have a big climb I’m training for I’ll do less BJJ and more aerobic training and if I don’t have anything planned for the mountains I’ll focus more on BJJ. It also makes it nice to be able to switch things up.
Hope this helps!