The muscle pain below the clavicle may be caused by the following reasons: 1. It may be caused by a strain here, which is often seen when the shoulder on this side of the patient is overstretched, which may cause a strain on the muscles here and lead to pain in this area. 2. A large number of push-ups may cause muscle pain in the pectoralis major muscle below the clavicle. The pain may be more pronounced when the patient does chest expansion exercises and stretches. 3. caused by peripheral nerve lesions, for example, when the patient has neurogenic cervical spondylosis, there may be radioactive pain in this area, which the patient may mistake for muscle pain. Finally, the pain in this area may also be related to visceral-related lesions, such as angina pectoris and myocardial infarction, which may produce involvement pain in this area.