Structural and molecular study of the supraspinatus muscle of modern humans (Homo sapiens) and common chimpanzees (Pan troglodytes)

Objectives To analyze the muscle architecture and the expression pattern of the myosin heavy chain (MyHC) isoforms in the supraspinatus of Pan troglodytes and Homo sapiens in order to identify differences related to their different types of locomotion. Materials and methods We have analyzed nine supraspinatus muscles of Pan troglodytes and ten of Homo sapiens. For each sample, we have recorded the muscle fascicle length (MFL), the pennation angle, and the physiological cross‐sectional area (PCSA). In the same samples, by real‐time quantitative polymerase chain reaction, we have assessed the percentages of expression of the MyHC‐I, MyHC‐IIa, and MyHC‐IIx isoforms. Results The mean MFL of the supraspinatus was longer (p = 0.001) and the PCSA was lower (p