The rear block is a bit of a mystery to the sport of track and field as various camps will cue and direct athletes to either hot lift, or push, or spike down. I am a purist in a sense that I believe that Tom Tellez is right about simply applying force behind you is the reality. How much and what direction is tricky as many sub elite athletes simply can’t use blocks as effectively with the settings they see on TV (WC or OG). Trying to emulate what they see is always path to failure unless the application of force is adjusted so the execution is matched with one’s abilities. One factor that we must look at is not just being a parasite to EMG readings to the set position in the start as fascia is contractile in nature and will not show up on surface or invasive EMG studies. Having the toe curled in slight extension set’s up the fascial connection of the ankle by preloading the triceps suri, creating a complete push. The weight and center of mass is slightly forward, enough to get a mechanical advantage but not too much that the pretension of the glutes and hamstrings are lost. Many athletes complain about a long or hard front leg push when the rear block and hip are not matched correctly. The pretension is mild, meaning you don’t want to loose the elastic rebound from the forces of the quad and posterior chain or be locked up tight.
I am doing my Level III Thesis paper on block starts and hope to be finished by January 1st. Also I am submitting two papers for NSA and Techniques Magazine on similar considerations.