20 Rep Squats and Cardio

I’m 68 and have been lifting for awhile did some powerlifting in the late 80s and 90s had a hip replacement a couple of years ago and used weight lifting and cardio for rehab decided I’d give the 20 rep squats a try my question is what kind of cardio should I do I have been on a Monday Wednesday Friday weights with 40min on the elliptical and abs on Tuesday and Thursday I’ve also done some HIT in the past so think I can handle 20 reps started at 135 hoping for 225 I’ve done that for 4 sets of 8 just not sure how intense or light I should do cardio I want to flush out the lactic acid but don’t want it to affect my squats

Stick with the steady state stuff. Like treadmill at 3.5-3.8 MPH. The squats are going to be muscular system and nervous system taxing. Don’t add on top of that with intervals.