Have you ever tried Scott Abel’s quad blast?
If not, I suggest you try it sometime
Quad blast goes as follows:
25 deep speed squats
12 alternating lunges/leg (24 total)
12 alternating jumping lunges/leg (24 total)
15 jump squats
Max. 30 seconds rest between exercises, if you are hardcore try to complete the circuit three times
Note: keep your hands on the back of your head if possible