I posted some of my shoot with Elena on Facebook recently and had a bunch of folks ask how I did the blur effect. Back in the day, this was accomplished by using the zoom ring on your lens while shooting really slow, or some other pain in the butt method. Today much easier and the results are much more predictable.
I shot these with the sun in a particular position in the image, and ended up with some really cluttered backgrounds. I tried to edit out the power lines and other junk, but it was taking forever. I decided to try this, and it worked quite well.
I used the Radial Blur filter in Photoshop, the reworked the image using layers and the layer mask.
You can place the filter over the image for best effect, and then work it to suit your taste.
The bottom photo didn't need background work, but I thought the effect really fit the jumping image.