Left-sided back pain, like a fork in the air, may be related to the following causes: 1. There may be a strain of the back muscles. This condition is often seen when the patient does a wide range of activities involving the trunk, after which the left back muscles are strained, the patient may feel pain, stiffness and unfavorable movement of the back, and some patients may also describe it as feeling like the back is propped up on a stick, unable to move. 2, there may be a transient muscle spasm. This condition is often seen when the patient suddenly stretches or bends over to pick up something with the left upper limb. In this time, the patient will often suddenly feel the pain of the left side of the back, like a fork in the air, but after a period of massage and rest, can get significant relief. 3, there may be heart-related diseases. In coronary heart disease or angina pectoris, myocardial infarction when the onset of this type of disease, there may be pressure-like pain on the left side of the back, this type of pain often makes the patient mistaken for muscle pain, in fact, sometimes life-threatening situation. Therefore, it is recommended that patients with such conditions and heart-related diseases should go to the emergency department of a secondary or higher hospital as soon as possible.