I have laid flat on my back on a padded floor while wearing a blindfold and with music playing in the background and let people jump off of tables onto my stomach. I won’t know when they jump but they can see if my muscles relax thus leaving my internal organs more vulnerable. I can only keep them flexed for so long before I get tired. I do insist that most of the impact especially from the heels be on the muscular part of my tummy and not the ribs and absolutely nothing below the belt.