"sling" type pack probably won't work well for you.
I'm assuming you'll need to carry non-camera stuff, either inside or attached outside ... food, clothing layers, 1st aid kit etc. Plus at that level of activity the pack will need to be firmly held in place on your body. The "sling" type packs are good for light hiking, bicycling etc. but beyond that I would not recommend them.
Thanks i will look into that one as well. As for amount of
physical activity, when i am skiing i am on the slopes all day
(6+hours) and when blading normaly anywhere from 10 to 60 miles at