I generally pack 20 to 25 lbs including 3 qts. of water. The quality of the pack makes a huge difference. 25lbs in a well designed, well fitted pack will wear you less than 15 lbs in a poorer pack. Many can pack 60..80..or 100 lbs., and many of us have to to pack out animals, but I wouldn't recommend doing it if you don't have to. In the long run most will pay for. Muscle strength isn't the problem. Our skeletal structure really isn't designed for it. I wrecked my knees packing heavy loads in steep country.