There are many references in books relative to the physics of Aikido. "Aiki Secrets: Six Precepts and the Dynamic COB" is an interesting read. There is also good stuff in an e-book entitled "Injury and Skeletal Biomechanics". The 3rd chapter is titled "Using the Knowledge of Biomechanics in Teaching Aikido". You can find the e-book and chapter at
http://www.intechopen.com/books/inju...eaching-aikido.
There are numerous others that are not on the top of my head at the moment, but I'll add to this post after the drugs wear off...