Asthenia: Weakness. Lack of energy and strength. Loss of strength. Myasthenia refers to a loss of muscle strength, as in myasthenia gravis. Asthenia is from the Greek asthenes, from a- (without) + sthenos (strength). From Brain and Nervous System Resources Relieve Spasticity IssuesAdvice for Living With Myasthenia GravisUnpredictable Days With Myasthenia Gravis Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19