Does p90x cause strain to my mcl?

No: P90x is a proprietary exercise progam that emphasizes mixing different types of work outs to confuse muscle memory; with the sessions lasting approximately one hour a day, six days a week for 90 days. Like any other exercise or work out program, you can sprain or strain your mcl or other areas by over doing it. You are not any more likely to injure your mcl with P90X than any other program.

It can: Lateral movements put a strain on the collateral ligaments. P90x has several exercises that can put stress on your collateral ligaments. All exercises are good if done carefully and if you are experiencing pain with certain exercises on p90x then substitute for the ones that bother your knee with one that doesn't.

No more than: Any other exercise activity that has you involved in either twisting motions at the knee or participating in exercises that involve lateral movements.