By measuring the physical activity level (PAL) of individual Tsimane men and women over 24-hour periods using a combination of spot observations and accelerometers, combined with heart rate monitors, Gurven and his team found is that while the Tsimane are, indeed, physically active more so than average Americans their PAL is not so great that it separates them from that of developed populations. "We found that while the Tsimane are more active than we are, there's a decent amount of overlap," he said. "Tsimane are not more vigorously active than athletic Americans with a high activity level. In fact, Tsimane do not spend much time in 'vigorous' activity, but instead spend a lot of time in light to moderate activity. Rather than characterizing the Tsimane as vigorously active, I'd more safely say they are not sedentary."
The researchers also examined issues related to obesity and body mass index (BMI). "One idea is that we're less active than we used to be, so we get heavier," Gurven explained. "But that's actually kind of controversial. The heavier you get, the more weight you have to move around. So even though you may be less active, you could be expending more energy. There's plenty of data that even when people are experimentally manipulated to increase their activity levels, after a three month period, their weight doesn't shift all that much. Or it shifts and goes back again."
That might be due to increased appetite and subsequent excess food intake, Gurven suggested. "Depending on your hunger levels, you might be eating more than the increase in your activity can accommodate, so you end up gaining weight. When we looked at people's BMI and levels of physical activity, we found no relationship. People with higher BMI's weren't less active than people with low BMI's."
That finding, he said, is consistent with the idea that it's not physical activity, but excess food intake that is more responsible for the "obesity epidemic" of th
|Contact: Andrea Estrada|
University of California - Santa Barbara