Several people have questioned my assertion in the New York Times interview that physical activity has not changed much in the past thirty years. My claim is partially based on work by Klaas Westerterp and John Speakman, who are two highly respected researchers in the field. Klaas gave a very nice talk on the topic at a metabolism workshop at NIMBIOS in 2011. His slides are here. What they basically did was to compare total daily energy expenditure (DEE) measurements to basal energy expenditure (BEE) over time. The ratio of DEE to BEE is called the physical activity level (PAL). The higher the PAL the more of the energy you burn every day is due to physical activity. Klaas and John showed that PAL has not changed significantly since 1980 and if you squint hard enough at the plots in the slides it looks like it may even have increased a little. While we seem to be very sedentary now, people tend to forget that we were also very sedentary thirty years ago.