Sudden soreness and weakness of the right arm may be caused by overwork, acute injury, cervical spondylosis and so on. 1. Overwork: strenuous exercise or physical labor, no rest, may lead to excessive accumulation of local lactic acid metabolites, causing sudden pain and weakness in the right arm, reasonable rest is generally able to gradually alleviate the symptoms. 2. Acute injury: muscle strain or external blow, resulting in damage to the right arm, there will be soreness and weakness, pain is more serious, may also be accompanied by swelling, subcutaneous bruising and other symptoms. 3. Cervical spondylosis: Suffering from neurogenic cervical spondylosis, improper daily care may lead to a sudden aggravation of the condition, compression of the nerves will cause right arm pain and weakness, accompanied by neck and shoulder pain, numbness of the upper limbs and other symptoms. It is recommended to consult a doctor for timely examination and treatment if your right arm suddenly becomes sore and weak.