Abstract

A "back of an envelope" calculation suggested an average decline in energy expenditure in the United Kingdom from the years after World War II to 1995 of around 800 kcal/d.³ At an energy cost of around 50 kcal/km for a 70 kg man,⁴ this suggests a decline in activity levels equivalent to walking about 16 km less per day. More recently, a comparison of activity levels of hunter-gatherer populations with those of individuals in modern Western societies suggested that the average daily difference may be equivalent to walking about 19 km.⁵ In an attempt to validate these estimates, we recently mocked up a small experiment for a lifestyle television production (Burke's Backyard). Our experiment was designed to compare activity patterns in Australian settlers of 150 years ago with modern-day sedentary office workers. We then attempted to calculate differences in terms of distance walked daily to compare with the previous estimates.

Methods

Seven male actors aged 30-60 years who work at "Old Sydney Town", a historic theme park north of Sydney set around the early 19th century, were selected to represent a historically active group. The men are paid to play the role of early Australian soldiers, convicts and settlers for about eight hours every day. They agreed to wear a TRACMOR during waking hours for one week, and were asked to avoid the use of modern technology as much as possible when they were not working at the park during the week. In an attempt to further authenticate this process, five of the men lived on the premises in convict huts for up to four days and nights. A second group of seven male modern sedentary workers, aged 30-60 years, including accountants, information technology personnel, doctors, a taxi driver and an entertainer, were also given TRACMORs to wear during waking hours, and were asked to continue their normal lifestyle over the course of a week. All records were downloaded into a computer program developed by the developers of the TRACMOR at Maastricht University in the Netherlands for analysis of results.

Results

Discussion

More telling are the implications this has for physical activity recommendations for optimal health and weight management. Recent government recommendations suggest an added daily energy requirement of 30 minutes of accumulated mild- to moderate-intensity activity.^10,11 However, for a 96 kg sedentary office worker, such as in this study, this would account for perhaps an extra 200 kcal/d, which is 300-800 kcal (the equivalent of walking 5-13 km) short of the 500-1000 kcal difference estimated here. These findings support the suggestion that, if the evolutionary perspective (which has dominated almost all of human existence) is indicative of requirements for optimal health, an increase in activity levels up to three times those recommended in modern guidelines may be necessary.⁵

Supporting this, data from the United States Weight Control Registry, a database of people who have lost more than 14 kg and maintained this for at least five years, have shown that people who achieve the greatest benefits are consciously active for up to 80 minutes a day.¹² This is about three times greater than current recommendations.^10,11 These figures are based on people who have been previously obese, and maintenance of weight loss may be more difficult than prevention of weight gain. Nevertheless, it is an awesome task, in the absence of a major environmental change, to expect these activity levels to be met in our society.

The figures presented in this study should be interpreted with caution. Although we used a validated modern movement-sensing device,¹³ the results involve only small numbers under artificial conditions. In their present form, they merely add support to other attempts to calculate human activity levels over time and provide an indication of the activity requirements needed to correct these secular changes.

References

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Authors' details

Masstricht University, The Netherlands.
Neeltje Vogels, BBiolSc Student;
Klaas R Westerterp, PhD, Professor of Human Energetics, Department of Biological Sciences.

Reprints will not be available from the authors.
Correspondence: Professor G J Egger, PO Box 313, Balgowlah, NSW 2094.
eggergjATozemail.com.au

©MJA 2001
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