It’s inserting short, hex head screws into the lugs in the outsole (ie, the bottom) of the shoe For an excellent write up on how to do this, read Matt Carpenter's webpage, "The Screwed Shoe".
Hawk Hundred 100/50/26.2 - 2012
Hawks Ridgeline aid station Heartland100
Coleen's Sweaty Ass Night Run, July 2011, Prairie Center, Olathe.