There are several reasons why bone is heavy, mainly as follows: 1. In a physiological situation, the weight of bone is relatively heavy compared to other tissues, mainly because of the higher density of bone compared to other tissues. 1/3 of the interior of the bone is organic matter, mainly collagen-like, and the other 2/3 is inorganic matter, mainly calcium phosphate, calcium carbonate, calcium chloride, etc. Organic matter will make the bone tough and flexible, while inorganic matter will make the bone hard and brittle, and will be more sunken and denser.2. In pathological cases, it may be due to local osteophytes, bone tumors, infections, inflammation and a series of other factors, resulting in large and excessive deposits of calcium salts inside the bone, which will cause the density of the bone to be higher compared to normal bone. Of course this increased density is not a good thing, and along with the increased density, the brittleness of the bone is greatly increased, thus making it susceptible to pathological fractures.