The causes of sore and weak feet are as follows: a. Muscle strain of the feet: recent large amount of physical activity can cause lactic acid to accumulate in the feet and calves, so there will be soreness and discomfort in the ankles and calves, and at the same time, there will be a feeling of weakness. Second, lower limb venous reflux obstruction: lower limb venous thrombosis can lead to blood reflux restriction, blood stagnation in the foot and calf, there will be local swelling, soreness and weakness. Third, varicose veins in the lower extremities: due to venous valve insufficiency, it also leads to restricted blood return to the foot, and after too much walking there will be a feeling of swelling and weakness in the foot.