..this is an e-mail I received from Dr. Clayton concerning some questions I had about DAP:
Dear Bruce:
DAP (Diagonal Advanced Placement) describes the order in which the diagonal limb pairs contact the ground in gaits like trot,
passage and piaffe. Before the days of slow motion photography, it was assumed that the diagonal limbs hit the ground synchronously,
but we now know that this is not the case.
In gait analysis, we measure the time between fore and hind limb contacts in milliseconds. We assign a positive value if the hind
hoof hits first and a negative value if the front hoof hits first. Synchronous contact is zero.
In the 1980s, Mikael Holmstrom did a research study in which he compared the scores awarded for the gaits by experienced judges with
the things he measured using slow motion video. He observed that horses with positive DAP (those in which the hind hoof hits before
the front hoof) received higher trot scores from the judges.
In my own research, I've found that the hind hoof hits the ground first in horses that have their withers and shoulders elevated
relative to the haunches. In these horses, when the hind hoof contacts the ground the forehand is so elevated that the front hoof
does not reach the ground. It's only after the joint so the hind limb compress somewhat that the front hoof contacts the ground.
When you watch these horses move, they have an uphill way of going and the contact of the diagonal pair look like an airplance
coming in to land. Horses that make contact with the front hoof first appear less elevated through the withers.
DAP doesn't imply that there's a phase when the front limb is the only one in contact with the ground.
In passage, the hind hoof always contacts the ground before the diagonal front hoof.
In piaffe, the order of contact for the diagonal pair is very variable between horses. In general, horses with a better piaffe are
more likely to have the hind hoof hit before the front hoof though. I analysed this in horses at the Barcelona Olympics - the horses
that won the individual medals were also those that had the greatest positive DAP.
I hope these thoughts are helpful to you.
Best wishes,
Hilary
