<s>[INST] When  do about 45 to 50 sit-ups I get this bg knotts right below my belly button. It's rock hard, and i have to stay in the lay down position with something cold covering it up for atleast 20 mins for the knott to go down. I can also barely breath when this happens. What is it? [/INST] you are probably having an umbilical hernia, which increases in size as u do more strenuous excersise. it's good that it reduceses on lying down, but this May not happen always, in which case u get an irreducible hernia which can lead to an emergency. avoid lifting weights, doing strenuous excersise. consult a surgeon and plan for a repair of the hernia. </s>