The big ones after taking a flight of stairs or a brief period of exertion are often called "transitional
PVCs." They get this name because your heart and body are transitioning from a state of relative rest to one of activity and exertion. I almost always get a
PVC about two steps after I get to the top of a flight of stairs. These transitional
PVCs are as benign as any other.
If you think about what's going on inside you, it makes sense - about halfway up the stairs your body realizes - yikes! She's putting her body into gear - let's let loose some adrenaline so we can keep up. The adrenaline flows, excites some already excited heart cells, and bzzt! A skip.
The ones you have 10 minutes in sound like about the same thing. Try this once - if your normal warmup to full exertion is 5 minutes, allow yourself 10 minutes next time. A nice, slow ramp-up. It might make a difference, but it might not. Sometimes it does for me.
When I had my month-long event monitor on I was spending nearly every night on the treadmill, trying to force my heart into doing those bad things I told all the nice doctors were happening. Just about every time, when I got in the 130-140
bpm range, which was 15-20 minutes in, I'd get a few
PVCs (3 or 4). At first I was hesitant to even record the
PVCs, because I knew what they were and wasn't concerned about them (I've had ten years practice - that helps). But my cardiologist told me to not try to be the judge of what's important and what isn't - she told me to record everything and let her sort it out. So I did. And there was nothing in any of my rhythm strips that she was concerned about.
Hope that helps.
Jeff