Understanding and Training Hip Flexion?

A recent post on my website forum (www.michaelboyle.biz) made me realize that often a short answer to a complicated question doesn't work. A few of my readers seemed to think that all of the recent talk about a weak psoas muscle or an under-active psoas muscle might just be people being trendy. I for one strongly disagree. I think my increased knowledge of the biomechanics of hip flexion is one of the most valuable things that I have learned in the past five years. The problem with understanding hip flexion in general and the psoas muscle in particular is that we use the term "hip flexor" as a generic term to apply to five muscles, four of which have distinctly different leverage positions from the other one. . . . (to read the remainder of this article, please log in below.)