The plantaris muscle is a small muscle located in the back of the lower leg that forms part of the calf. According to autopsy studies, the muscle has a great variance in size, thickness, and length, and is thought to be entirely absent in around ten percent of the population. It is made of a muscle belly and a thin tendon. In its entirety, the muscle ranges from seven centimeters to thirteen centimeters in length. Due to its small size in relation to other muscles in the calf and knee, it has often been mistaken for a tendon or a large nerve. Subsequently, there is relatively little study of the muscle itself, and its role is not fully understood. There are currently calls for further research to be done into the plantaris muscle, not only to discover its role and involvement with the calf, knee, and ankle, but to improve diagnosis of injuries to it. It is thought that injury to the muscle is relatively common, though currently accurate diagnosis can only be determined through MRI scans. Doctors believe that improvements in understanding the plantaris muscle would aid diagnosis and treatment of common injuries, including the colloquially named"tennis leg."
Written and medically reviewed by the Healthline Editorial Team
In Depth: Plantaris