I'm not good with abbreviations, what is MFR?
Warm up is usually started by stretching out the hamstrings, followed by hip adductors then quads. Ten minutes on a treadmill, slight incline at just below a jogging pace. That is followed by using a leg extension machine with low weight (~80 lbs) at 3 sets by 20 reps. I'll then do some plain squats (no weight, just the movement), somewhere around 50 squats, followed by 50 more with the bar (45 lbs).
If I get through that with no knee pain, the rest of the workout is fantastic. Sometimes, the pain will show up and then go away during the warm up, in which case the workout is usually fine. If the pain is there once I'm done with the last set of squats, I'm screwed.
I can't recreate the pain right now (go figure, I'm not doing legs today either), but best I can describe it is under the patella, and the patella ligament itself.
The pain isn't sharp, it's more of a dull pain, but very sudden and powerful. Imaging doing a squat, and some prick comes along and kicks you right under the knee cap.
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Only if I can get the pants in blue, I don't do pink.
I don't think it is a temperature issue, it'll happen if it's 20 degrees out in winter, or 100 degrees in the summer.