The ProLog has been used in competition on a number of occasions. I saw it in action at Red Hills HT, Hugh Lochore actually employed them primarily to reduce stifle injuries on the entry into the water. For the 3* class it was a bounce and the 2* a one stride. In both cases the ProLog was employed for both A & B elements.
Interestingly, for the first element it was built conventionally, supported only on the ends. For B element for both classes the pole was supported in the centre also, Hugh’s reason being it was a low fence from memory only 80cm high. At that height it is not recommended to be frangible (for the frangible pin a fence needs to be normally at least 95cm high to use the pins, source USEA Cross-Country Obstacle Design Standards & Frangible Pin Handbook). Hugh saw real potential in reducing the number of stifle injuries by using a log that would absorb some impact.
Given the number of impacts on the logs at the end of the day, we could see that this application certainly has some merit. Here are some pics of them, one log was broken in the two star class. The feedback was that it broke due to the high number of impacts (most horses gave it some sort of rub) rather than any single impact.
On the other hand, they were used for the first time at the Rolex 3DE 4 Star event. The log was used on the entry into the “Head of the Lake”. It was only broken once, by Capt. Geoff Curran and The Jump Jet the ProLog snapped clean in half meaning that they stayed up top and safe. There was a video on youtube of it but for some reason it has been pulled. Here is a photo on the Chronicle of the Horse website. This second pic is amazing.
If anyone has a copy of the video, I would love to see it again.