Is our lifestyle too sedentary?

Are we fighting thousands of years of evolutionary history and the best interests of our bodies when we sit all day?

That question is at the core of a fascinating new study of the daily lives and cardiovascular health of a modern tribe of hunter-gatherers. The findings strongly suggest that we are born to be in motion, with health consequences when we are not.

Evolutionary biologists have long believed that the basic structure of human bodies and genomes were set tens of thousands of years ago, when we were hunter-gatherers. The hunter-gatherers from that time who were most adept at following game or finding tubers won the baby-making lottery and passed along their genes to us, their descendants.

But we no longer live in a hunting and gathering world. Mostly we live in offices and in front of screens, where we sit and have food brought to us, creating a fundamental mismatch between the conditions that molded our bodies and those that we inhabit.

The health consequences of this mismatch are well-established. Many scientists have pointed out that the easy availability of food creates an “obesogenic” world, in which we easily gain weight and develop related health problems. There also has been considerable research linking sedentary lifestyles with health concerns.

But we have not really known just how much physical activity may be natural for us. The fossil record is evocative but inexact, unable to tell us precisely how our ancestors lived, while most past anthropological studies of living hunter-gatherers have been observational, meaning that researchers have estimated activity patterns.

But estimates can be wrong. So for the new study, which was published last month in the American Journal of Human Biology, researchers from Yale University, the University of Arizona, and other institutions decided to bring high-tech rigour to their ongoing examination of a group of African hunter-gatherers.

For many years, the scientists had been studying and tagging along on hunts with the Hadza, a tribe in Tanzania that lives by subsistence hunting and foraging for berries, honey, baobab fruit and tubers. As part of past research, the scientists had measured the men’s and women’s blood pressures, lipids and other markers of cardiovascular health. They now asked some of the tribespeople if they would wear heart-rate monitors around their chests. The scientists focused on heart rates since most modern recommendations about exercise involve intensity. We are told that we should aim for at least 150 minutes per week of moderate exercise or 75 minutes of vigorous exercise.

The simplest way to determine exercise intensity is with heart rate. By most definitions, moderate exercise raises someone’s heart rate to between 55 and 69 per cent of that person’s maximum heart rate, while vigorous exercise raises it to between 70 and 89 per cent. Maximum heart rate can be calculated from a formula based on age. 46 of the tribespeople, ranging in age from young adults to people in their 70s, agreed to participate, donning a chest strap for up to two weeks during different seasons of the year while they went about their daily lives.

©2016 The New York Times News Service