Basically: When an MG patient uses one set of muscles it leads to weakness of other/remote muscles.
This is even more so if ischemic conditions are created during the exercise (such as by putting a blood pressure tourniquet on the arm).
Mary Walker thought it was an important diagnostic sign (probably like the SFEMG is seen today).

She was asked by a colleague-we tried the arm constriction method you showed us on a patient suspected to have MG and got no results. Could this be considered a negative test for MG?

http://annals.org/article.aspx?articleid=689226

http://neurologyminutiae.blogspot.co...is-pearls.html

http://www.ncbi.nlm.nih.gov/pmc/arti...01551-0056.pdf

http://content.karger.com/produktedb...E2005053001051