When sleeping at night, there are several reasons for the soreness of the left foot: First, the patient suffers from serious lumbar spine related disorders, such as herniated discs in the lower lumbar spine, spinal stenosis, hyperplasia and protruding discs after compressing the spinal nerve roots, causing sciatic nerve pain in the lower limbs, and the symptoms can be manifested as soreness and pain along the lower back, buttocks all the way to the rear lateral side of the thighs and calves, the back of the feet, and the soles of the feet. Second, patients with poor blood circulation in the lower limbs, such as deep vein thrombosis, deep vein valve insufficiency and other poor blood circulation in the lower limbs, can also manifest as soreness and pain in the leg muscles. Thirdly, it is common in young patients, after engaging in intense physical exercise during the day, the lactic acid accumulated during the night when sleeping causes calf muscle pain in the process of release.