As they get older, people tend to reduce their levels of physical activity. Why didn't evolution engineer us so that people could maintain a decent quality of life as they inevitably slow down?
Researchers argue in a new paper that we aren't meant to reduce our physical activity as we age. The 'active grandparent hypothesis' is a hypothesis.
Researchers have begun to uncover beneficial processes that physical activity can promote, such as maintaining a lower blood pressure. It's not clear why these mechanisms cease to work the same way in the absence of physical activity, especially in older people who rely on them to maintain their health and quality of life.
David E. Liberman, Harvard evolutionary biologist and lead author of the study, draws on previous findings to explain why physical activity reduces illness and injury.
Evolutionary biologists tend to argue that evolution hasn't had a lot of time to adjust since only recent human generations have been able to put their feet up.
This might explain why we should keep an eye on our ancestral habits and stay active as we age, but it doesn't tell us why our ancestors stayed active for so many years.
The authors break down some of the assumptions we have about ancient humans.
Human lifespans have been thought to be short, but hunter-gatherers who survive infancy and childhood tend to live on average seven decades, approximately 20 years past the age at which they cease reproducing, and fossil evidence shows that extended human lifespans were common by 40,000.
Older individuals in social groups were selected for their ability to impart knowledge and skills to humans, and also their ability to provide food for their children and grandchildren.
The authors note that the number of daily steps older Americans take decreases by about half between the ages of 40 and 70, but daily walking distances among hunter-gatherers such as the Hadza decline only modestly with age.
The authors suggest that the allocation of resources to physical activity over other biological processes may have helped to prevent certain health issues from arising in the first place.
Under certain conditions, physical activity meant potentially harmful excess energy wasn't allocated to fat and reproductive tissues, where a large literature exists today demonstrating the negative health impacts of excessive fat storage.
The authors have put forward a new hypothesis that suggests that regular physical activity meant that energy resources were allocated towards the repair and maintenance of tissue and cells that degrade with physical activity, and as a result come back stronger.
This includes the repair of tears in muscle fibers, the release of exercise-related anti-inflammatories, and the healing of microfractures. These responses are blunted without physical activity.
We run a greater risk of developing diseases if we don't exercise, with studies showing that it can take anywhere from half an hour of moderate exercise a day to an hour of intense effort a week.
The introduction of technologies that have replaced human labor, such as motor and electric vehicles, agricultural equipment, and self-guided machinery, have resulted in a growing number of health-related issues among the elderly, despite this wisdom.
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 study was published in a journal.