The inability to turn your left foot up and use force may be related to nerve compression, herniated discs, and muscle fatigue. Left common peroneal nerve entrapment syndrome can cause abnormal nerve function, resulting in a feeling of weakness in the left foot. Surgery is usually required to remove the nerve compression and restore normalcy. When the cervical and lumbar herniated discs cause serious pressure on the nerves, the left foot will not be able to turn up and use the force, mostly accompanied by pain and numbness, muscle atrophy and other symptoms. After a long time of running or climbing and other strenuous exercise, calf muscle fatigue will also briefly appear left foot can not be up with the feeling of force, generally appropriate massage, rest will be able to fully recover. Traumatic injury caused by ankle tendon rupture will also appear can not be up with the feeling of force. If the left foot can not be up with no force, it is recommended that the patient go to the hospital to improve the examination, to clarify the cause of the disease, regular treatment.