Quenton Conant

I'm a little confused by something said a few posts ago.

so, we all know that impact sports, certain weight bearing exercises, etc can have a positive effect on bone density. But what is the minimum needed to achieve this?

I've always been under the impression, maybe mistakenly, that especially with weight bearing exercises i.e. weight lifting specifically, that in order for it to have an effect on your bone density there is a minimum amount of weight that needs to be lifted each repetition as opposed to cumulatively.

For Example, doing 30 arm curls with 2.5lb dumbbells is a weight bearing exercise, but not necessarily enough to stimulate that change. whereas lifting a 15lb dumbell for the same total accumulated load would. Please keep in mind that this is only to illustrate the point I'm trying to get at, and not a statement of fact.

What I'm getting at is why would bench pressing a weight for 15 reps have an effect while doing a pushup would not?

why would doing squats do this and climbing a hill on your bike not?

What mechanisms, or physical differences in forces are at play?

Are there minimum percentages of body weight required, or a specific force to be lifted against gravity required?

I realize some of it is in relation to conditioning, but I'm curious to know more.

I spent most of my childhood, teens, etc. skateboarding, doing martial arts, and other activities where there was alot of falling, hitting, impact, weight lifting etc so this issue really hasn't been an issue I've paid much attention to until the last few years.

Any professionals out there able to distill my ramblings and answer the question I'm trying to ask?