I never have and never will carry my backpack for "conditioning". I do my day walks without a pack - much more enjoyable. I am saving my old knees and joints for REAL BACKPACKING! I would hate to think that I wasted my knees for a conditioning hike. I do very little "conditioning" at all! I bike or walk a few hours about 3 times a week. That's all. I do a few shorter 2-5 day trips early season. They are not "conditioning" hikes - but trips I really want to do, new places to see. Life is too short to waste energy on suffering through conditioning hikes!