What is the Mary Walker phenomenon?
Fatigue and weakness of the forearm muscles develop in myasthenic patients when the forearm muscles are exercised with a cuff around the upper arm, inflated above systolic pressure to occlude circulation (ischemic exercise).
After the cuff is deflated, myasthenic symptoms in the rest of the body may worsen within minutes in some patients.
This phenomenon is named after Mary Walker, the physiologist who first described it in 1938, and is also present in the myasthenic dog.
Although its mechanism is not clear, it may be due to transient lactic acidosis, because lactic acid binds calcium and reduces available ionized and serum calcium.
Experimentally, lactate infusions increase weakness in patients with Myasthenia Grevis much more than in controls.
