Board Thread:Theories and Speculation/@comment-4688597-20150531233756/@comment-5936871-20150601011742

The Uzumaki come from the Senju who come from Asura. Therefore, they all have very powerful bodies. The Uzumaki were specifically stated to have powerful life-forces and large chakra reserves, and the Senju were stated to be prodigious in all forms of jutsu. However, it can be easily assumed that the Senju possess the same abilities as the Uzumaki since the Uzumaki come from them. I also believe it was stated somewhere (although I forgot) that Senju inherited strong physical energy and the Uchiha inherited strong spiritual energy. Yang relates to physical energy and Yin relates to spiritual energy, so since their bodies are stronger I think that makes them more suitable for Sage Mode and being Jinchuriki.