I am 77 years old and always walked a lot for excersice. Then I started 10 years ago walking long-trips (from place to place for several weeks pr. year) with a heavy rucksack. For me 'heavy' means 7-8 kilos - being a small and thin woman. This helped!! The osteoporosis-scanning after three years showed several points of still-stand - not worse. But also 2-3 points had improved! I now add the rucksack to most walking-trips!