Most everyone knows that exercise is good for you. Some people may even recite the reasons why it keeps muscles and joints strong, and how it fights certain diseases. But how many people can tell you the story of why and how physical activity was incorporated into human biology?
A team of evolutionary biologists and Harvard biomedical researchers are testing it (sometimes literally) in a new study published this week in PNAS. The work presents evolutionary and biomedical evidence showing that humans, who evolved to live many decades after they stopped reproducing, also evolved to be relatively active in their later years.
Researchers say that physical activity later in life diverts energy away from processes that can compromise health and into the body’s mechanisms that extend it. They hypothesize that humans evolved to remain physically active as they age and, in doing so, to allocate energy to physiological processes that slow down the gradual deterioration of the body over the years. This protects against chronic diseases such as cardiovascular disease, type 2 diabetes, and even some cancers.
“It’s a widespread idea in Western societies that as we age, it’s normal to slow down, do less, and retire,” said Harvard evolutionary biologist Daniel E. Lieberman, lead author of the paper. “Our message is backwards: As we age, it becomes even more important to be physically active.”
The research team, which includes Aaron Baggish and I-Min Lee of Harvard Medical School, believe the article is the first detailed evolutionary explanation of why lack of physical activity as humans age increases human activity. risk of disease and reduces longevity.
Baggish, 47, who also serves as a cardiologist for the New England Patriots and US Soccer team, and Lieberman, 57, are longtime running partners and often discussed ideas that appeared in the newspaper during races. morning 5-10 miles.
The study uses the ape cousins of humans as a starting point. The researchers note that apes, which generally live between 35 and 40 years in the wild and rarely survive after menopause, are considerably less active than most humans, suggesting that there was selection in human evolution not only to live longer but also to be more physically active.
“We basically evolved from TV addicts,” said Lieberman, who has observed wild chimpanzees twice in Tanzania and was amazed at how many days they spend “sitting on their bottoms, digesting.”
This is especially jarring when compared to contemporary hunter-gatherers, who average around 135 minutes of moderate to vigorous physical activity per day. That level of movement, around six to 10 times more than the average American, is thought to be a key reason why hunter-gatherers who survive infancy live for about seven decades, roughly 20 years past the age in the time that humans stop having children, and also enjoy a longer “lifespan,” which is defined as the years of life spent in good health.
The researchers examined two pathways by which lifelong physical activity reallocates energy to improve health. The first involves shifting excess energy away from potentially harmful mechanisms, such as excess fat storage. The team also identified how physical activity allocates energy to repair and maintenance processes. The document shows that, in addition to burning calories, physical activity is physiologically stressful and causes damage to the body at the molecular, cellular and tissue levels. The body’s response to this damage, however, is essentially to rebuild stronger.
This includes repairing tears in muscle fibers, repairing cartilage damage, and healing microfractures. The response also triggers the release of exercise-related antioxidants and anti-inflammatories and improves blood flow. In the absence of physical activity, these responses are less activated. Cellular and DNA repair processes have been shown to reduce the risk of diabetes, obesity, cancer, osteoporosis, Alzheimer’s, and depression.
“The key take-home point is that as we evolve to be active throughout our lives, our bodies need physical activity to age well. In the past, daily physical activity was necessary to survive, but today we have to choose to exercise, that is, to do voluntary physical activity for the sake of health and fitness, ”said Lieberman.
The research team, which includes graduate students Timothy Kistner and Daniel Richard, hopes the study will make that message harder to ignore.
Levels of physical activity have been declining around the world as machines and technology replace human labor. A recent study from Lieberman’s lab showed that Americans get less physical activity than 200 years ago.
The advice of the researchers? Get up from the chair and get some exercise.
“The key is to do something and try to make it enjoyable and keep doing it,” Lieberman said. “The good news is that you don’t have to be as active as a hunter-gatherer. Even small amounts of physical activity, just 10 to 20 minutes a day, substantially reduce the risk of mortality. “
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