Postactivation Potentiation or PAP has been a technique that has been researched and thrown around in strength/conditioning circles for quite some time now. In this blog post by Bret Contreras, respected strength coach and co-author of "The strength of evidence podcast" does a very nice job of summing up all the recent evidence and includes additional posts from other respected strength coaches like Charles Poliquin.
So what is PAP before you read the post? Well, I quote:
"The underlying principle surrounding PAP is that prior heavy loading induces a high degree of central nervous system stimulation, resulting in greater motor unit recruitment and force, which can last from five-to-thirty minutes (Chiu, Fry, Weiss, et al., 2003; Rixon, Lamont, & Bemden, 2007)"
For example, one might perform a heavy resistance exercise such as squats, followed up by a vertical jump. It is thought that the vertical jump would be increased due to the increased muscle activation and CNS activity from the heavy squat.
Typically, there are two theories for how PAP works. One theory involves an increase in a phosphate for the synthesis of ATP of myosin regulatory light chains, which are proteins of muscle contraction, during a MVC. Essentially what this does is allows actin and myosin binding to be more active due to calcium irons released, which as we know leads to enhanced force production of muscle. When a max voluntary contraction occurs, there is greater muscle activation which means a greater time calcium ions are in the sarcoplasm and therefore the greater the phosphorylation of myosin light chains. What's this all mean? Faster rates of tension and contraction rates.
The other theory involves the H-Reflex, short for Hoffman Reflex. This reflex is basically the spinal reflex extracted by the group 1a afferent muscle nerves becoming excited. The group 1a afferent muscle nerves are special nerves conducting impulses to muscle. What is believed is that the H-reflex is enhanced with PAP. This means the rate and efficiency of nerve muscles is greater.