I'll just echo what these guys said. Since MG gets worse with repetitive (treadmill test) or sustained (holding an object) activity, your legs were simply getting weaker due to repetitive activity.

Don't ever ignore chest pain. It could be costochondritis or other inflammation, narrowing of the arteries, which don't always show up unless you do a nuclear scan, a blood clot, hole in heart, electrolyte imbalance, etc. A LOT of things can cause chest pain. A good doctor can figure that out.

Again, make sure they check your oximetry. They should do it while you are walking around too. In MG, the first thing that happens when our oxygenation goes lower due to weak chest wall muscles is that our heart beats harder to get us more oxygen. So, your pulse will go higher! Then, if you sit down with that oximeter on, your pulse will come down but then so will your O2 saturation! Checking oximetery for an MG is like an art form because we get worse when we DO something.

And, yeah, you could have a thymic tumor. Or thymic hyperplasia, which just means it's bigger than what it should be for your age.

I hope you get solid answers soon. In the meantime, don't overdo or push! Like Teresa said, it's quite dangerous for an MGer to do that.

Annie