That very well might be true. Part of the support for this line of reason is that work-related energy expenditures have been going steadily down. To quote the NPR piece:
[Dr.] Church took the findings one step further and calculated how many calories were no longer being burned. He found it was about 140 fewer calories burned a day for men and 120 fewer calories burned a day for women. "That doesn't sound like much, but when it's day after day after day, it adds up," he says.I found data agreeing with this claim. Dr. Joyner, in a piece titled How the USA Got So Fat incorporated the same data from Church's paper on his own blog:
I understand the argument that Americans (as well as the rest of the world) are doing less leisurely physical activity. What I don't agree with is the 'job' portion of that is significant. From my understanding of health, the 100 - 150 Calorie per day downturn is insufficient to warrant any drastic action, e.g. office campaigns to get workers burning more Calories while on the job. Granted sitting in the same position all day is bad for you, but that's not quite the same as working up a sweat.
Let me provide a counterargument via anecdote. One day -a few years back- our lab had to move all our instruments from one room to another. Except for very light-weight items, it was not our job to move these things, rather my boss employed professional movers to do the heaving lifting; some of our equipment weighed over 300 lbs. While on break, the movers were chatting to each other. One of the younger guys said "I've really been meaning to get in shape". The other nodded, agreeing they probably should do the same. Certainly they were strong, but no, to be perfectly honest, they were not in amazing shape (one smoked, the other two had beer guts). But I remind you these were professional MOVERS.
Anecdotes can be dangerously misleading, but the above supports the basic idea that simply using your muscles more on the job is not enough. 100 Calories a day is one extra granola bar a day. Our bodies strive for equilibrium, hence doing math like
100 Calories/day * 365 days ~ 10 lbs of fat
is very misleading since our body will burn less fuel per day as we thin slightly. Burning an extra 100 Calories will not lead to losing 10 pounds in a year. Rather than drudging up a bunch of papers and links to show this, let's agree on widely held consensus we need at least 30 minutes of exercise a day to keep fit (in reality we should be doing closer to an hour). Assuming you run at a very leisurely pace of 10 min/mile, and assuming you burn about 100 Calories per mile, then you'd burn 300 just from that absolute minimum volume of cardio. If the very basic standards can triply compensate this 50 year decline in on-the-job effort in half an hour. The fact is that many in physically demanding jobs yield workers sometimes, but not always, in great shape. I think we can surely agree how much effort we expend at work has never been a serious factor in keeping fit.
If you can reverse 50 years of on-the-job slacking with 10 minutes of cardio, your smoking gun lies elsewhere.
I'm glad this study was done, as it rules out what could have been an important factor in keeping fit. I am worried there will be many who decide this article implies we should be doing squats in front of our computers. Such intermittent activity will help with repetitive strains and the like, but will not work as a substitute for leisure exercise. The key word there being leisure. Leisure exercise is the kind we're all familiar with, and such activity should is not, and has almost never been since ancient times, a substitute for workplace efforts. It is best to consider work and play actives separate, essential, and complementary.