Weakness in both legs can be a result of neurological disorders, diseases of the musculoskeletal system, and electrolyte disorders. 1. Neurological disorders: peripheral nervous system disorders, such as Guillain-Barré, can cause weakness in both lower limbs. 2. Skeletomuscular disorders: For example, a herniated lumbar disc compressing the sciatic nerve can also cause weakness in both legs. Patients with myasthenia gravis may also experience weakness in both lower limbs at an early stage. 3. Electrolyte disorders: for example, hypokalemia, hyperkalemia, at this time, patients may also have abnormal sensation of limbs, nausea and vomiting. In addition to diseases, if patients have too little or too much exercise for a long time, they may also have double lower limb weakness. If patients still have double lower limb weakness after rest, they need to go to the Neurology Department of the hospital as soon as possible.