I found some information a while ago while suffering with patellar maltracking which is common in cyclists due to an overly developed lateralis. In order to strengthen the VMO, EMG studies show that unilateral movements recruit more VMO whereas in bilateral movements, the lateralis - larger and stronger - attempts to dominate and usually does - resulting in an imbalance over time.
Whether this imbalance is causing pain or is merely aesthetical, I found using a particular exercise works extremely well.
Split squats in a smith machine done in a particular way. Weight can be kept to a minimum here - the emphasis is on the squeeze. Start with the working leg forward. As you descend, only drop down to 45 degrees of knee flexion where you will hold it for a deliberate 2 second count. Squeeze back up but do NOT lock out at the top, keeping tension on the VMO the entire time. 12-15 deliberate repetitions should really make the VMO start to fire like mad, shaking, possibly cramping up. Signs you're effectively targeting it. You may be tempted to lock out at the top at this point - don't. It's supposed to be uncomfortable. Try 2 sets per side for a couple weeks at the beginning of your leg routine.
Grim
