This deep range mobility and strength drill challenges ankle stability, glute strength and the oblique sling. Each human body has a anterior and posterior oblique sling that double helix from the bottom of the foot around the back of the leg to the pelvis. In positions such as a sprint or in this case skating or sliding, end range strength with proper position of the spine results in higher performance. We are contracting our leg muscles while in a end range ankle position. Do not do this for high volume unless it is bodyweight or light. For weighted, I recommend 2-3 sets of 3-4 reps.