The main causes of numbness in the thighs after prolonged sitting are.
Sciatic nerve numbness, normal people sciatic nerve from the sacral plexus, through the pear-shaped muscle, towards the rear of the lower limbs, sitting position, the sciatic nerve in a state of tension, generally will not produce numbness, abnormal sensation. However, too much time (especially unilateral exertion resulting in excessive strain on the pear-shaped muscle) can lead to excessive tension on the sciatic nerve and excessive compression by the pear-shaped muscle, resulting in abnormal sensation in the thigh.
Ischemic. After prolonged sitting, the blood vessels in the lower limbs are compressed, leading to ischaemia of the nerves and tissues and producing numbness.