A couple of the most common chronic pain areas or poor functions are the knees and ankles. Poor dorsiflexion makes for a shallow, compromised squat pattern, which eventually affects knee health.
I like kneel-to-squats because they impose severe dorsiflexion, which trains the knee to move forward over the toe under zero external load (trust me, you won't need any additional weight) and builds ankle mobility and knee strength. The foot also gets a great plantar flexion to strengthen its intrinsic muscles.
If you're worried about how bad this would hurt since you've hardly ever squatted below parallel in your life, I've got you covered.
Simply shorten the range of motion. See how I'm kneeling to one mat in the video? Stack up 3 or 4 mats, so your point of contact is shallower. As you get stronger, work your way down. Do sets of 15 reps.
One more thing I like about this is the constant tension. You're staying tight while kneeling to prepare for the "up" phase, but you're also remaining in a half-squat on each rep – you never get to stand until the set's over. This hits the quads hard, translating to stronger and healthier knees.