Although palpation, joint range of motion, and measurement by hardness meter are used to represent muscle hardness, all of them have some weak points. Palpation is easy and cost-effective, but it is a subjective method. Joint range of motion may represent muscle hardness indirectly, but it is influenced by bony abnormalities, tight capsule, shortening of the ligament, and adhesion of the joint. Hardness meter is an objective method, but it measures the total hardness under skin tissue. US elastography produces a two-dimensional hardness map, so we can measure the hardness of each muscle. Compartment syndrome is characterized by severe pain and extremely hard muscles caused by high intra-muscular pressure. Delayed diagnosis and treatment are known causes of severe physical impediment. US elastography made it possible to visualize the affected muscles, allowing us to perform selected fasciotomy with small skin incision and intra-operative monitoring under US elastography. As muscle hardness changes with the status of activities of daily living and sports, knowing muscle hardness may be useful for improving performance and avoiding injuries associated with daily and sports activities.