The answer to your question would require an entire book. Plus it is still a work in progress.

The top handlers that I know of who are actively experimenting with it are Rachel Sanders with her BC Fable, Stephanie Spyr and her young BC Rage, and Theresa Rector from Canada with her Kelpie.

I re-trained 2o2o to a running contact with my lab, with the help of my wonderful teacher Gail Mahood.   It took about 6 months (and the purchase of an AFrame for the backyard so that we could practice and proof it little and often).  It took me a while to perfect (!) my handling.  There are probably many different methods but mine was

(1) get the striding right - goal was to get my dog to jump the AF apex such that she is now set up to stride onto the contact zone vs. launch into outer space -- This can be done by starting with the AF at about 3 feet in height, or at full height, depending on whether your dog naturally jumps the apex.  Mine did. Lucky me 

(2) Teach dog to run under a hoop -- We used a PVC hoop (home-constructed) that my dog was trained to go under - Hoop shaped like a rectangle and about as wide as the AF.  Height - about 2 inches higher than my dog's head when running.   It stands freely i.e. I built horizontal legs that lie along the ground perpendicular to the plane of the hoop.  First I taught my dog to run under the hoop on the ground on the ground and marked the correct "run under the hoop" behavior with treat and a verbal "yes".     You can also try putting a plate on the ground beyond the hoop 

(3) Use hoop to cause dog to touch the contact.   The hoop was placed 1.5 dog lengths beyond the end of the AF (you can start further away if your dog thinks it might want to jump the hoop).  What you want to do is run beside your dog, parallel to the AF and very close, be slightly ahead when they cross the apex, and then decelerate as the dog takes the hoop... Mark the correct behavior (touching contact zone) with a "yes".  You can place the reward on the ground beyond the hoop or reward from your hand, while you face straight.  Keep your shoulders straight and reward the dog after passing under the hoop by leaning slightly back like a ballet dancer.  Don't lean in

(4) Fade the hoop.   I would alternate runs with and without the hoop.  I also tried using no hoop but instead a low jump a few strides beyond the AF such that my dog would have to collect herself a bit at the bottom of the AF so as to stride correctly to the jump... but I don't know anyone else who tried that approach.    Laser focus your  eyes on the contact so that your dog gets the idea.  

(5) Proof it -- Start to build distance between you and the AF, make the next obstacle not be straight in front of the AF, but to the side.  

Other things that might work to help avoid jumping the contact.... Sylvia Trykman suggested telling your dog what the next obstacle is as they start the descend the AF .  I saw this work for my class-mate's dog.   I believe Sylvia's rrunning contact training method was originally to start her young dog with lowered contact obstacles and raise them up over time.

Another thing that is worth thinking about -- I actually bought an AF with extremely good traction to it -- The board has sandy rough surface between the slats.   I think that this made my dog more confident.  I also found that practicing at slightly below full height (5 foot 2 ish) some of the time instead of 5 foot 6 or over 6 feet if your a USDAA fiend(!), makes a big difference in getting the behavior that you want

Best of luck... Remember too not to overdo it -- 10 repetitions max per session else your big dog might tire.  

One of our students has experimented with her golden to targetting a down on the ground after the frame.

 This is a dog who always ran nicely up on the ascent, but walked carefully (upright) down the ramp and always looked uncomfortable because her center of gravity was too high for her to safely run down.

 Since she has targetted the down (with reinforcement for each rep, cookie or toy) for  a couple months now, this dog has started anticipating the down, and began to lower her body on the descent, and adding speed.  She is now doing more of the border collie creep, where the dogs creep-run (and can do it quite fast) on their down contacts.

In a trial situation, rather than actually give the dog time to GET into her down, she can go ahead and cue the next obstacle and in essence, has created a running contact.  To keep the fast-creep-run, she still reinforces an actual down/hesitation MOST of the time, which is simple body-memory conditioning.

 I was fascinated to observe the dog changing her own manner of descent by anticipating getting into her down position as fast as she can to get that cookie, and I eagerly await to see if other dogs tend toward the same thing, whose handlers choose the lie-down at the base.

To really establish this as an actual running performance, it would be ideal to start with the lowest frame, teach the down at the base first (maybe use a table next to the ramp to let the dog step over on to the contact, through and lie down on the ground at the base, then backchain to the complete low frame to down position, teaching the dog to RUN to the target and down quickly.  Then, gradually increase the height so the dog can feel how to adjust his body with the higher heights. It seems if the dog is really keen to the running-to-position (and that can first be taught on the flat, quite frankly), the entire performance can be shaped with a LOT of speed from the get go, if the handler doesn't overface the dog (as in novice or young dog) by raising heights too quickly.

 If, instead of lowering the center of gravity, the dog would try to leap from the top to the down position, this would be a good time to teach the target behavior by going through/under a wicket, (again, on the flat first so the dog can learn his job) so the dog clearly understands the criteria is about getting as close to the frame as fast as possible, not launching off of it!

Barbara and The Symphony of Hounds

I was really excited to hear this works untill I realize the student you were describing was me

 I am glad you think it is going well as I think I have settled on this four on the floor method although I think I have a long way to go in proofing it. 

Bonny 

I know that some people who never take away that hoop. The hoop is /always/ there, so the dog expects it in competition. Kind of the same way how some obedience trainers will -always- train in a prong; the dog is only in a choke chain during competition.
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Sunrise Sweet Tess TT CGC
English Springer Spaniel