Soreness and weakness of the legs below the knees are mainly related to lumbar spine lesions, degenerative diseases, overwork or myofasciitis. 1. Lumbar spine lesions: When lumbar spine lesions occur, such as lumbar spinal stenosis or lumbar intervertebral disc herniation, they may compress the nerve roots and affect the motor and sensory functions of the lower limbs, resulting in the symptom of soreness and weakness of the legs below the knees. 2. Degenerative lesions: degenerative lesions in the knee joints are likely to produce symptoms of weakness and soreness in the lower legs below the knee, and even accompanied by pain. 3. Excessive fatigue: If you have long time weight-bearing activities or strenuous exercise, you will feel excessive fatigue of the calves, which will easily lead to the phenomenon of soreness and weakness of the calves below the knees, which will be relieved by yourself after taking a rest. 4. Myofasciitis: If inflammation occurs in the calf area, such as aseptic inflammation of the muscle or fascia, the stimulation of inflammation will easily trigger the symptoms of soreness and weakness of the calf below the knee, and even accompanied by pain and swelling. Soreness and weakness of the calves below the knee may also be related to vascular diseases of the lower limbs, if the symptoms are more serious and last for a long time, you should go to the hospital in time to find out the specific cause of the disease, and then targeted treatment under the guidance of professional physicians.