Just did a scouting trip in 346 this weekend and man, there's nothing quite like hitting the mountains with a heavy pack to remind you that you have a LONG ways to go to still be in "elk shape"....man I'm sore.
It's not just the cardio and the stamina, it's the joints....ankles, knees, back. Going UP and DOWN those mountains with a load is killer, especially on the knees for me. Plus you start feeling the aches and pains of muscles used when actually HIKING hard, that you don't alway replicate in the gym.
No training quite for elk hunting like actually getting up in the mountains and DOING it.