I wonder if the authors of the study considered Non-exercise activity thermogenesis (NEAT). This is the energy expended for everything we do that is not sleeping, eating or sports-like exercise. It ranges from the energy expended walking to work, typing, performing yard work, undertaking agricultural tasks and fidgeting.<p>If they only selected white-collar / desk workers for the study, then it's possible that people expended more NEAT back then in their office environment. Just looking at movies from the 80s, you definitely see more physically active offices than what you see today. People walking around to pass memos, papers, attend physical meetings, etc in the 80s has been replaced with people sitting at a computer to send emails, chat messages, meeting invites, etc.<p>Also,the nature of jobs people do today is a lot different. There was a study that showed US men's grip strength has been decreasing from generation to generation. No surprise given that the US economy has been changing from a manufacturing and agricultural based economy to a services one.<p>Here's an article mentioning the study - <a href="https://www.npr.org/sections/health-shots/2016/06/13/481590997/millennials-may-be-losing-their-grip" rel="nofollow">https://www.npr.org/sections/health-shots/2016/06/13/4815909...</a>