I am a surgeon and I stretch.
But I have my doubts.
Consider this.
When a knee gets arthritic, it often becomes bowed. This places extra load (stretch) on the outer ligament.
Thus, this ligament is placed under increased load -stretch - at every step. Given that the average person takes 1,000,000 steps per year per knee (at least), we should see massively stretched ligaments in these knees.
But we don’t. You see the occasional slightly stretched lig in disease such as rheumatoid arthritis but not in otherwise normal individuals.
So, the body responds to load, as suggested in previous posts in this thread. Extremely efficiently. See Wolfe’s law for bones - the same applies to ligs.
So, the only way to actively lengthen a ligament would be to overcome the natural body repair and strengthening systems.
Just reducing the load is no good. The body is far more sensitive and subtle than that.
A continual stretch beyond the collagen tensile stresses would be required. And maintained.
Skin? Yes. Tunica? Probably. Susp ligament and deep fascia? I suspect not.
Doesn’t stop me trying but I suspect that this is a self defeating battle.