I usually work out legs pretty hard on monday and friday. will doing high intensity cardio for 20 minutes on tues and sat hurt recovery. i know that doing light workouts the day after are supposed to help because it gets blood flowing , but when i do the cardio sessions the day after i can really feel the lactic acid. is this allright or should i change something. also, my main purpose of the cardio is recovery, not to keep in shape or anything.
In a word, yes, you are hurting your recovery. If you insist on doing aerobics, try doing a light session right after your weight training, or later the same day. I think that most trainees find 2 hard leg sessions a week to be too much to start with; perhaps you should consider Ian King’s hip/quad dominant set of workouts, or having separate quad and hamstring days.
I personally have my doubts about this "get the the blood flowing"/"remove the waste products" theory of aerobics anyway. The amount of total blood that will flow through your legs in a 24-hour period might be altered by 5% by doing a 20 minute cardio session, and that's probably an overestimation. In the meantime, you are definitely increasing your cortisol output. This sounds like one of the old-timer training myths to me, along the lines of consuming dessicated liver tablets.
To assist recovery, Charles Staley recommends around 20 minutes of moderate intensity cardio on non-lifting days, 3 times per week. He trains atheletes. I also think he warns against putting impact aerobics like the treadmill or the stairmaster the day before or after leg day, and suggests something like an elliptical runner or a stationary bike instead.
As for dessicated liver tablets, some experts still like them, or at least certain brands, Dr. Serrano, for example. Brian