The story of the human body evolution health and disease sparknotes

Thus, total time spent in inactivity is associated with the accumulation of higher levels of circulating triglycerides and cholesterol, increasing cardiovascular disease (CVD) risk ( 9, 10). For example, Hamilton and coworkers ( 10, 17) have argued that, with little muscle activity requiring fuel, sitting leads to reduced production of enzymes that hydrolyze lipids for energy (e.g., lipoprotein lipase). Hypotheses seeking to explain the negative health impacts of sitting often focus on these prolonged periods of muscular inactivity. Resting and inactivity reduce metabolic energy costs, often considered a key target of natural selection ( 14), so why is inactivity harmful for the human body? Here, we test the hypothesis that the ways in which urban populations rest, rather than the amount of time spent resting, represents an inactivity mismatch with an evolutionarily relevant hunting and gathering lifestyle, and propose that this mismatch may contribute to the negative health impacts of sedentary behavior today.Дuring periods of inactivity, individuals living in industrialized societies generally sit in chairs or recline, greatly reducing muscle activity and energy costs needed to support the body ( 15, 16). The effects of the competing demands of activity and inactivity on the body represent an evolutionary paradox. However, a separate set of physiological changes occur during inactivity and may also lead to chronic diseases in sedentary populations, even in individuals who are highly active ( 9 в‡“ в‡“ в‡“вЂ“ 13). Thus, many suggest our physiological reliance on moderate-to-vigorous physical activity (MVPA) to prevent chronic diseases is a product of this evolutionary history ( 5 в‡“ в‡“вЂ“ 8). The evolution of the genus Homo was marked by a shift toward high levels of physical activity in a hunting and gathering lifestyle that included long-distance walking and possibly running at moderate to high intensities ( 1 в‡“ в‡“вЂ“ 4). Interventions built on this model may help reduce the negative health impacts of inactivity in industrialized populations. Based on our results, we introduce the Inactivity Mismatch Hypothesis and propose that human physiology is likely adapted to more consistently active muscles derived from both physical activity and from nonambulatory postures with higher levels of muscle contraction. However, nonambulatory time in Hadza adults often occurs in postures like squatting, and we show that these вЂњactive restвЂќ postures require higher levels of lower limb muscle activity than chair sitting. Using a combination of objectively measured inactivity from thigh-worn accelerometers, observational data, and electromygraphic data, we show that hunter-gatherers have high levels of total nonambulatory time (mean В± SD = 9.90 В± 2.36 h/d), similar to those found in industrialized populations. We tested the hypothesis that nonambulatory rest in hunter-gatherers involves increased muscle activity that is different from chair-sitting sedentary postures used in industrialized populations.

Here, we examined inactivity in a hunter-gatherer population (the Hadza of Tanzania) to understand how sedentary behaviors occur in a nonindustrial economic context more typical of humansвЂ™ evolutionary history.

These inactivity-associated health risks are somewhat paradoxical, since evolutionary pressures tend to favor energy-minimizing strategies, including rest. Health risks from sitting are generally linked with reduced levels of muscle contractions in chair-sitting postures and associated reductions in muscle metabolism. Recent work suggests human physiology is not well adapted to prolonged periods of inactivity, with time spent sitting increasing cardiovascular disease and mortality risk.

The story of the human body evolution health and disease sparknotes