I am heading to Nepal for ABC trek in March/April 2015. I am fat, never really exercised and lazy person. But for the trek, I have been practicing on getting fitter. I have been walking 10 kms everyday for past 3 weeks, losing kilos and gaining stamina. How fit one need to be? And what should one do?
The route to ABC is very steep at some places. It can take a toll on your knees. So, I suggest you to take some knee protection with you. If you are walking 10km everyday, then you should be fine. Even if you get exhausted, you can find lodges along in the way where you can always take rest. Enjoy- ABC is very scenic and beautiful especially Ghandruk.
I've heard that you should be able to hike for at least five hours a day. If you can do that, you should be okay. Good luck!