This type of stretching is very similar to the active static stretch except that dynamic stretching, the joint is going through a range of motion. By this I mean that you are actually moving the joint at the same time while sensing a little bit of a stretch on the muscle. It’s a good, simple stretch to do as a warm-up prior to your event. Be cautious with this particular type of stretching because you can actually strain the muscle if you go too quickly. This is actually a common stretch that’s often done incorrectly.
If you ever watch athletes doing some of their warm-up activities, quite often we will see them bending forward to stretch out the back of the legs and at the end range of motion are bouncing up and down reaching for the ground or toes. Now, this might be OK the well conditioned athlete and an acceptable thing for them to do, but for the vast majority of individuals bouncing at the end range of motion can only lead to an injury. The better way of doing this would be to start from an upright standing posture position and bend forward to the floor backup then return to the upright position again. Gradually you get a little further each time. Bouncing at the end range of motion can only lead to an injury.
My suggestion is to go through a small range of motion first (video above). Gradually increase the range as a muscle starts to feel more warm up. This might take 10 to 20 seconds to gradually increase that range of motion. For instance, stand up straight then bend forward a little bit and return to upright. Go slightly further each time until you can bend forward as far as you can comfortable (see diagrams above). It’s a gradual increase in the range, so don’t overdo the pull.