Firm muscles This finding has been described in Arthrogryposis, distal, type 5 and Glycogen storage disease II. HP:0003725 A state of increased firmness (i.e., a reduced tendency to yield to pressure) of skeletal muscle tissue. This finding is ascertained by palpation and is to be distinguished from increased muscle tone (abnormal elevation in the resting tension of a muscle, leading to stiffness and resistance to movement). UMLS:C1850656 Abnormal skeletal muscle morphology