Everyone knows that exercise is good for you. Some people can tell you why it keeps your muscles and joints strong. How many people can tell you the story of how physical activity was built into our biology?
A team of evolutionary biologists and biomedical researchers from Harvard are taking a run at it in a new study. The work shows that humans evolved to be relatively active in their later years after they stopped reproducing.
The researchers say that physical activity later in life shifts energy away from processes that can compromise health and toward mechanisms in the body that extend it. They theorize that humans evolved to remain physically active as they age, and in doing so allocate energy to processes that slow the body's gradual decline. It protects against chronic illnesses such as cardiovascular disease, type 2 diabetes, and even some cancers.
Daniel E. Lieberman, the paper's lead author, said that it's normal to slow down, do less and retire as we get older. As we get older, it becomes more important to stay physically active.
The paper is believed to be the first detailed evolutionary explanation for why lack of physical activity as humans age increases disease risk and reduces longevity.
Baggish and Lieberman are both cardiologists for the New England Pats and U.S. Soccer, and often discuss the ideas that went into the paper during 5- to 10-mile morning runs.
Humans' ape cousins are used as a jumping off point. The apes are less active than most humans, and this suggests that there was selection in human evolution to be more physically active.
Lieberman, who has seen wild Chimpanzees in Africa and was surprised by how much of their day is spent sitting on their butt, said that they evolved from couch potatoes.
This is especially shocking when compared to contemporary hunter-gatherers who average about 135 minutes of moderate to vigorous physical activity a day. The hunter-gatherers who survive childhood tend to live about seven decades, 20 years past the age at which humans generally stop having children, because of the high level of movement. Fossil evidence shows that these extended lifespans were common 40,000 years ago, contrary to the belief that human lifespans were short.
The years of life spent in good health is the key health benefit of physical activity.
Researchers looked at two pathways that reallocate energy to improve health. Excess energy is dealt with away from potentially harmful mechanisms. The team identified how physical activity allocates energy. The paper shows that physical activity can cause damage to the body at the cellular and tissue levels. The body's response is to build back stronger.
Repairing tears in muscle fibers is one of the things this includes. The response causes the release of exercise-related anti-inflammatories and improves blood flow. The responses are less active in the absence of physical activity. The risk of diabetes, osteoporosis, cancer, Alzheimer's, and depression have been shown to be lower with the use of the cellular and DNA repair processes.
Our bodies need physical activity to age well because we evolved to be active throughout our lives. In the past, daily physical activity was necessary in order to survive, but today we have to choose to exercise, that is do voluntary physical activity for the sake of health and fitness.
The research team hopes the study makes it harder to ignore the message.
As machines and technology replace human labor, physical activity levels have been decreasing. A recent study from Lieberman's lab shows that Americans are not as active as they used to be.
The researchers have advice? Get out of your chair.
Lieberman said the key was to do something and to make it enjoyable so you would keep doing it. You don't need to be as active as a hunter-gatherer to be active. Even a small amount of physical activity reduces your risk of death.
The story was told
Harvard University provided the materials. Juan Siliezar wrote the original. Content can be edited for style and length.
