The tendon is composed of collagen fibers, which do not have the ability to contract, and its role is to transmit the contraction force of the muscle to the bone tissue. The tendon fibers are corrugated at rest and disappear when stretched. Microdamage to the collagen fibers can occur with excessive stretching, and even tendon rupture can occur. What are the symptoms that are easily confused with it? 1, arm muscle strain Arm muscle strain is a kind of muscle strain, muscle in the movement of the sharp contraction or excessive strain caused by the injury. 2, muscle strains muscle strains are injuries caused by sharp contractions or excessive stretching of muscles during exercise. This is easy to happen during long run over, pull-ups and sit-up exercises. After a muscle strain, the strained area is in severe pain, and the muscle tension can be felt by hand as a hard lump, with obvious pain to the touch, local swelling or subcutaneous bleeding, and obvious restriction of movement. 3, muscle soreness Muscle soreness caused by exercise is a very common injury experience for people involved in sports. Generally speaking, muscle soreness caused by exercise can be divided into two types: acute muscle soreness and chronic (late-onset muscle soreness). Acute muscle soreness is different from muscle strain, but refers to the temporary ischemia of the muscle, and the soreness caused by the phenomenon, only muscle for intense or long-term activity will occur, muscle activity will disappear once the end. Usually, acute muscle soreness will be accompanied by muscle stiffness.