There are several possible causes of pain when lifting the left arm: First, acromion impingement syndrome, which is caused by the formation of bone spurs or congenital abnormalities in the acromion, which cause pain in the shoulder joint when lifting. If there is a tear in the rotator cuff, pain can occur when lifting the upper arm, which can be accompanied by weakness in lifting. Third, in frozen shoulder, there is often a limitation of shoulder joint movement in all directions, accompanied by obvious pain and stiffness, especially when lifting the upper arm, the pain is very significant, then the relevant X-ray and MRI should be performed for diagnosis and treatment.