Their sheer mass seems like a more obvious culprit. F=ma, and they do have so, so much F. Plus being less physically able to lift your body our of a wreck hardly helps them. I don't think I could lift my body if someone strapped a 100 kilo bag of goo on me and crashed me into a wall at 40mph. But no, it's really the either the chairs or the dummies that are at fault.