Many clothing makers use a set of measurements that are average for Americans. And since most Americans are fat now, they have large thighs and large biceps.

So many company's arm and leg warmers don't fit cyclists properly with their muscular but lean thighs and (relatively) skinny arms.

As someone pointed out, Castelli is a bit further ahead on this but they're also expensive and I've had a couple of clothing failures from them. Pads that fell apart and seams that came apart etc.

What I did with some Performance arm warmers would work equally well (or unwell) with leg warmers: I did a single s-fold at the top seam and put a couple of stitches in to hold the fold in. This works perfectly with the arm warmers and would probably work with the leg warmers equally well. The problem is that for me that large size was oversize enough that the fold didn't make it too tight and cut off circulation.

Your mileage could vary.