If you're already running 40 miles a week, I wouldn't think P90X would help you lose weight. You may actually gain weight as a result of the resistance training. Since you're running, you know that you have to make sure your caloric intake is high enough to fuel your body for those miles but not so high that you've got a bunch extra.

There are free calorie calculators online that will tell you what your net calories (per day) have to be to reach your goal. I'm using that in conjunction with P90X and it seems to be helping quite a bit. P90X had me at over 3000 calories, which is probably right...but the online tools started me at around 2600 and have decreased as my weight has decreased (down to about 2200/day now) and I'm consistently losing about 1.5-3.5 pounds/week.

If my knees could handle running, I'd do that instead of PlyoX (which I've been subbing in Cardio X anyways) on the Plyo day and maybe add it in on the Stretch/Rest day. Other than that P90X kinda wears me out. YMMV

Oh. Plyo Push-ups. I love those! I don't get airborne (probably), but they're still fun. And...CHOCOLATE MILK! Nom nom nom!

-mini