Is it impossible to increase skeletal bone mass, as opposed to just bone density?
If you search for
 - bone growth training
 - bone hypertrophy athletics,
 - bone diameter increase,
 - bone strengh hunter gatherer,
on google, you will find more articles than I could possibly summarise:

stimulation of longitudinal bone growth and widening of the joint space (cartilage hypertrophy) occur. The possibility of bony hypertrophy as a result of athletic training, especially with regard to increases in of bone density and bone diameter, should lead to incorporation of sports medical considerations into the prophylaxis and therapy of osteoporosis.

https://www.ncbi.nlm.nih.gov/pubmed/7856798

https://www.ncbi.nlm.nih.gov/pubmed/7478507

I have slender bones and it was the gain of muscle which helped me to balance my physique.