What is mobility anyway?
Mobility is the ability of a joint to move actively through its full range of motion.
It is recommended for athletes to have at least 15 degrees of ankle dorsiflexion --I like explaining it as: your knee should should be able to move over your toes 4-5" with your heel staying on the ground.
Give this test a try to see where you are:
1) Make a fist plus your thumb - put that against a wall
2) You can sit, kneel, or stand facing the wall - line your toes up with your fist (4" from the wall)
3) Drive your knee to the wall while you keep your heel on the ground
4) If you can touch the wall - You Pass
If you can not touch the wall - You get to work on this
The best part of this "test" is - that it can become the exercise.
If you are not yet able to get your knee to the wall. You can do just that as a practice.
One more thing - you may be wondering, "Why does this really matter?"
As you toe off, your knee does drive in front of your toe.
Get up and try it in slow-motion. See what I mean?
So when the ankle does not bend enough your toe off will be at a less efficient angle.
Ankle mobility can also effect injuries like: shin splints, plantar fasciitis, and even overall ankle stability.
Give it a try and let me know how you do!