From about 9-20, I just headed out in basketball shape with little specific training. Just spent some time jogging and doing step-ups with a heavy pack to get used to the straps some. Paid the price with shin splinting (from downhill) and pack strap soreness. Since I lived in the Central Valley, there weren't any convenient hills to climb/descend and no treadmills in those days to simulate uphill.
My primary sports the next decade were weightlifting, cycling, and softball (oh, and beer drinking). Again, no hills to climb. Did train a couple years stair climbing training (with weighted pack) in the 14 story building I worked in in Sacto. That left me in great climbing shape (I could finally out-climb my mtn goat father me age 30 and he 57). But again, plenty of strap soreness, shin splinting, and foot blistering. Stair climbs do not have the slanted foot angle needed to properly prepare the lower legs. And nothing beats hiking for prepping the foot skin.
~33-45 my primary sport was volleyball (beach, indoor, grass) with a bit of cycling. The jumping/darting sports (vball, bball, tennis, et al.) do a great job overall of prepping the ankles, knees, etc. Now in the SF Bay Area, I was able to mix in hill climbs (Mission Peak, Coyote Hills, Pleasanton Ridge) and spend more time doing useful work with the pack on. This eliminated shin soreness and much of the pack strap chafing.
~45-50 my primary sport was inline speedskating (~50km) with some cycling cross-training. Speedskating is awesome cardiovascular work and I learned a lot more about interval training and how to increase aerobic fitness, raise hematocrit, etc. Having good blood levels pre-hike allows me to camp about 1500-2000 feet higher the first night without my AMS symptoms cropping up and offset my small lung capacity.
50+ backpacking has become the primary sport. With the bulk of training coming with some kind of pack on my back hiking up/down some kind of hill, including intervals, I'm able to really be ready for my trips. This combined with better/lighter equipment has allowed me to keep my miles per day about the same over the years despite increased body fat and aging.
Injuries have cropped up, more in the last decade or so. Knee tendonitis; a couple of heel bone shards sticking into my Achilles (living with it, don't want the full year recovery from surgery); knee surgery; etc. But I was able to overcome a pelvis/back problem a decade back upon finally getting advice from a Dr. who know what she was talking about and preventative workouts from my (very) personal trainer. So there is good also. No more jumping or deep squats allowed though.
Since work is not currently in the way, I've added back regular weight training, core fitness, and balance work. Now if I could just get lean like Mav, I could do some real damage!
