It’s not a typo and yes it is a lot. The original poster, cabahagirl, mentioned OsteoStrong. You may want to check out their website—lots of useful info. There isn’t an OsteoStrong within 2 hrs of my home so I’m not able to sign up for their program but I think they are definitely on to something. I have visited ann OsteoStrong and, basically, they use 4 pieces of osteogenic loading equipment. Based on the goals OsteStrong sets for members my takeaway was that the weight needed for your upper body to build bone is different from the weight needed for you lower body to build bone. When you are using their leg equipment (similar to gym leg press equipment but there are no moving weights, you just apply the force) they try to get you to hit a higher number than when you are using the equipment that you push with you hands (hope that makes sense). Also with that 4.2 times your body weight remember that when you are standing your body is carrying 1 x your body weight and different activities can increase that amount without the need to actually add more weight. For instance, jumping creates more force on your bones and can help stimulate bone growth. Also some sports are “better” than others at building bone. Swimming will not help your bones directly. As far as bone health is concerned running is better than swimming or biking for increasing one density. Additionally, studies show that socccer players have greater bone density than runners—the thought is that running is super-repetitive so it doesn’t challenge your muscles/bones enough, whereas with soccer there are lots of short brisk movements and sharp turns and stops that cause muscles to “tug” on your bones more and thus, stimulate bone growth. You might find this link very interesting and helpful https://americanbonehealth.org/exercise/bonesense-on-osteogenic-loading/