We have probably all grabbed a wall or a friend and done the basic quad stretch: grab your foot, pull it to your butt until your feel the front of your leg burn…
It works OK. However, if you choose a split squat instead, actively lengthening the quad while shortening the antagonist glute/hamstring muscles and then reversing the action, it not only mobilizes our walking, running, skipping pattern but also strengthens the hips and legs.
Additionally, you can load the split squat and really challenge your system. I always suggest high rep ranges: 8 reps or more/side.
If you add load to your trunk (goblet style, double racked kettlebell or a barbell) your trunk will need to go into lock down mode.
If you put the load below the waist (straight arms holding dumbbells or kettlebells), I suggest putting the weight down when you switch legs as you might need both hands to push off your front leg to stand up!