From the Research
Testing the plantaris muscle is challenging due to its small size and vestigial nature, and the most practical approach is to assess it indirectly through plantar flexion testing, as recommended by the most recent study 1. The plantaris muscle is a small, often vestigial muscle that works alongside the larger gastrocnemius and soleus muscles, making it difficult to test in isolation. There is no specific isolated test for the plantaris muscle alone, and its isolated dysfunction rarely causes significant functional impairment, as it contributes minimally to plantar flexion (less than 1% of total force) 2. Some key points to consider when testing the plantaris muscle include:
- Pain in the posterior calf may indicate plantaris injury, particularly if accompanied by a snapping sensation during activity 3
- Imaging studies like MRI are more reliable for diagnosing plantaris pathology than physical examination alone 4
- The plantaris originates from the lateral supracondylar line of the femur, has a small muscle belly, and a long thin tendon that inserts into the calcaneus, making it susceptible to rupture during sudden movements, often called "tennis leg" 1
- Anatomical variations of the plantaris muscle may cause mid-portion Achilles tendinopathy, tennis leg syndrome, or increase the risk of failure while harvesting the tendons 1
- Musculoskeletal ultrasound imaging can be used to guide the decision-making process and discern the optimal location for the application of instrument-assisted soft tissue mobilization in patients with plantar fascia-related pain, although this is not directly related to plantaris muscle testing 5