I think that everyone has different physical capacities and that any form of exercise will benefit you backpacking. For me i like working out at our crossfit gym, we do all our own programming and I personally like power and oly lifting. One thing I do like about these are that they dont turn us into body builders but just make you super strong so you can move a large load long distances more easily. I do like to also enjoy a trail run or bike ride but now that school has fired up i find less time for that.