I just recently returned from my first trip to Africa, we hunted in some pretty hilly terrain in Namibia. Being able to compare the physical requirements to other hunts I've taken in the North America, I'll offer this.
Diamondhitch hit it - the better shape you're in, the better off you'll be. You'll be able to hunt longer, harder, and be more in tune with your PH. Mine was a 27 year old that could run like a gazelle. I knew if I could keep up with him, I'd optimize my success and ensure a good hunt. I did just that, because I keep myself in good shape. After day 2 of our hunt, I was glad that I did. Talk with your PH and make sure he understands your limitations if you have any. I'm going back next year, and here's a few things I'll do to better prepare.
1. Plyometrics, or any form of jump training combined with balance. Will tighten your core, and put your feet in tune with the rest of your body. I found that walking, or running, in the rocky terrain placed a premium on being able to trust your legs and balance was key.
2. Hiking, with your boots. Get you a weight vest, and strike out in some hilly terrain. Don't just walk, see number 3.
3. Sprints, in some form of terrain. Practice sprinting, or minimally taking a fast jog, up and down hills for short distances. Walk a mile, then sprint at the end of it. More importantly, practice your breathing when you stop. I shot 7 animals on my trip, and 3 of them came at the end of long stalks where we covered ground quickly to take the shot. Being out of breath is part of it, and it takes some practice to slow your breath and hold a steady shot. The better able you are to quickly regain your breath and relax, the better off you'll be.
Just my thoughts. Hope they help, and good luck on your trip!!