Called the "gifted"ones, this type is genetically predisposed to great musculature gains. Usually very athletic looking, they have a good posture and are symmetric. For a bodybuilder or fitness enthusiast, this is good news! Mesomorphs are said to build muscle mass faster then most people can and to be able to loose fat rapidly when on the right diet!
This particular body type is generally predisposed to higher body fat % accumulation. Known to have a "soft look", it is harder for them to trim and tone through exercises and diet. The good news is that Endomorph bone structure is wide and strong. This can be a bonus for your bodybuilding endeavor
Hard gainers in other words! Long leg/arms, low body fat %, and small muscles. While some women wouldn't find it to be a problem to have some of the characteristics of this body type, men will probably see it in a different way!