A bout of weakness in both lower limbs may be caused by physiological reasons such as overexertion, but may also be caused by cervical spondylosis, lumbar spondylosis, knee disease, cerebrovascular disease, hypothyroidism and other pathological reasons. 1. Overexertion: Due to the accumulation of lactic acid and other metabolic products in the muscles caused by overexertion, resulting in muscle fatigue, the patient may experience a bout of weakness in both lower limbs when walking. 2. Cervical spondylosis: especially spinal cervical spondylosis, cervical disc herniation compresses the spinal cord and nerve roots at the back, and the patient may experience weakness of the lower limbs, a burst of softness, and a feeling of stepping on cotton and other symptoms. 3. Lumbar spine disease: lumbar disc herniation, spinal stenosis, lumbar spondylolisthesis and other diseases lead to the innervation of the lower limbs nerve compression, the patient can appear in both lower limbs a burst of weakness, sometimes accompanied by pain, numbness, and activity restrictions. 4. Knee diseases: such as meniscus injury, knee arthritis and other diseases can cause the patient to walk with a bout of weakness in the lower limbs. 5. Cerebrovascular diseases: such as Guillain-Barre syndrome, myasthenia gravis and other diseases, the patient can appear double lower extremity weakness, a burst of weakness, and finally developed into limbs and other muscle weakness. 6. Hypothyroidism: hypothyroidism caused by various reasons, the patient can appear double lower extremity weakness, a burst of weakness, generalized weakness, indifference and so on. Double lower limbs a burst of weakness may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.