The image posted is a Letter to the Editor submitted to USDF Connection in response to Dr. Clayton's article in Oct issue: "Unique Seminar Focuses on Measuring Rein Tension" (http://connection.epubxp.com/i/386281/0 article p. 26 - 31). The Letter to the Editor supports on-going research by a variety of experts in the usefulness of the "new" rein tension measuring device as a diagnostic tool for equine lameness, joint dysfunction and restrictions in the spine, pelvis, neck, and jaw, and training tool for horse-rider interaction. The Letter calls attention to the results of a particular questionnaire that supports the science of PRI and attempts to briefly and "all-inclusively" explain how the L AIC and R AIC muscle chains affect horse-rider interaction and performance. (Obviously all 8 muscle chains are involved, but I thought a simple explanation would be appreciated by the readership.)
I encourage you to read the article itself, not only because it is interesting but also because it raises PRI questions about horses.