There are many reasons for weak legs and feet, as follows: 1, cerebral ischemia can cause weak legs and feet, because the brain does not dominate the legs; 2, cervical spondylosis can also cause weak legs when walking, because the central cervical spondylosis compression to the spinal cord, can cause weak legs when walking; 3, lumbar spine diseases can also cause weak legs when walking; 4, joint diseases, aging joints, joint effusion in the elderly, can also cause weak legs when walking 5, lower limb artery occlusion, lower limb ischemia can also cause weak legs when walking. Generally, deep vein thrombosis will cause soreness and swelling of the lower limbs, and some patients dare not exert themselves when walking because of the soreness and swelling of the legs, and the soreness and swelling will be aggravated when they exert themselves, so it will also cause leg discomfort, but it will not cause the legs to lose strength when walking or fall down when walking.