Please see the following links for expert tips on training, biomechanics, saddle fitting, and more:
The following video provides excellent information on the mechanics of the horse's back. Our special thanks to Equitopia for allowing us to share it. The research done at UC Davis Veterinary School is particularly significant.
Please see the The Physics of Flexion, and The Physics of Collection & the ESM 2012 abstract for more information on the subject (Related Articles link).