Not sure about the weight loss but I find simple climbing or really any uphill activity (stairs or stadiums could work) with a day pack of moderate weight seems to build strength, endurance and your wind (depending upon pace) better than anything else I've tried. Everybody has their own ideas on what's best and generally speaking, what's best is something you'll actually do/maintain to the degree that it provides the results without injury. A brisk walk up a hill with a moderate amount of resistance, and perhaps just as or more importantly, the negative resistance downhill without lunging or using gravity as an aid, builds the type of strength and endurance that keeps you from getting sore when you are actually on the mountain. To much weight going downhill causes you to lunge rather than "resist" your momentum. Fatigue from weight going downhill and lunging also exposes you to injury because you grab more distance and speed with each step than what is prudent, which can cause a slip or slide. You never want a slip when training because that can contribute to a pulled muscle, tendon or twisted ankle and that can interfere with what your trying to accomplish which is simply enjoying your hunt without hurting and still being able to do what you need to do.
Something to think about... I had heel spurs on both feet. I suppose it came from running, a job that was standing and walking all day long and exploring the mountains when I had some time off. Anyway, I had the spurs removed but the doctor said I needed orthotics/arch support. Several times I stopped wearing them and within several weeks, I developed back pain. Not chicken little back pain. The kind of stuff that felt like a disk was slipping and my spine and the muscles around it were getting wonky. At the time I wasn't doing anything special other than grinding away at work with semi-long hours on my feet yet I was getting screwed up. I put my arch support back in my shoes and in about 3 weeks, I was more or less, fine. I did this a few times because I'm must be a little slow. Moral of the story... what's going on with your feet can definitely affect your back, and your back affects everything. Being fat is hard on your feet. Being fat and throwing on a back pack on top of it all is sort'a heading in the wrong direction. As an outdoorsman, your personal weight will affect your experience outside. I'm not an ultra-lite guy but don't overload yourself. Heck, the last time I went out, my 9 day pack was so heavy, I hyper extended my knee taking a step downhill and it dicked my up for a month or two. Reasonable body weight, reasonable pack weight. Truly... nobody much cares about your story anyway and embellishing it with "hero" details only makes you a hero in your own mind.
So... arch support in your shoes/boots. If you have back pain, don't overlook the soles of your feet. I pretty much always have some type of arch support in the out of doors cause I'm carrying loads that are beyond my normal body weight.
