The 3 strides are uprights. We had V poles on them to encourage the horse to make a really good shape and stay straight. The 3 strides have been shortened (more like 14-15 yards) so the horse is not allowed to rush or lengthen the stride or else you are going to send the uprights flying. The canter needs to be a short compressed one and the rider needs to use their upper body to help keep the canter going down the line.
We went down this line a couple of times. What often happens is that the horse often finds the last part of the three fences tough so be mindful when building the grid that its quite a tough gymnastic exercise for them.
After going down the three uprights we then moved onto the double of spreads. These are built on a regular 2 strides Again we had V poles to encourage a good shape and to keep the horse straight. This time the canter needs to be moved on so that you have more power to make the distance easily.
When you have jumped the spread you then mix it up and go from uprights line to spreads. All the time the rider needs to work hard to make sure the canter is correct and the horse is off the leg and listening. Nice and controlled and short for the uprights and then move the canter on so its more forwards and powerful for the uprights.
This is a progressive exercise so can be started smaller and built up.