"Kegel exercises strengthen the pubococcygeus (PC) muscle. You are using this muscle when you stop the flow of urine mid-stream - sort of a clenching that also tightens the anus. When you clench the PC muscle while you have an erection, you can make the penis jump up and down. When this muscle gets fully tightened it leads to ejaculation. A strong uncontrolled PC is often the cause of premature ejaculation.
For edgers, we want the opposite. There is no reason for edgers to ever do Kegel exercises. We want to relax the PC muscle and prolong the erection. Reverse Kegels involve gently pushing down on the pelvic floor, sort of like you're trying to push out a turd. You can also engage this by forcefully pushing out your urine stream (the opposite of clenching above). Once you get good at this, you can open and 'purse' your anus like lips puckered for a kiss. When your anus is this relaxed, you should be able to slide something small, like a pencil, into the rectum without any reaction from the anus, no tightening, etc. (Using something larger, like a dildo, will be too tight and create a reaction.) If you can stay this relaxed, you should be able keep an erection for a long time."
From this thread:
http://www.lpsg.com/294275-advanced-edging-techniques-from-a.html