By Liam Mannix
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You know exercise is good for you, so let me spare you the lecture. Today’s Examine is interested in a related but different idea.
Why do I need to exercise?
This is a surprisingly awkward question for exercise scientists. The evidence is clear: exercise is good for us. So good, even small amounts produce marked benefits.
Even small amounts of exercise are good for our health, but why did humans evolve that way?Credit: Joe Armao
But … why would evolution produce an organism that must spend 150 minutes a week doing things like running on a treadmill to maintain health? In the wild we don’t often see animals doing arbitrary exercise; even our closest living relatives in the animal kingdom, chimpanzees, walk only a few kilometres a day.
Organisms tend to try to preserve homeostasis – dynamic stability. So why is our body unhealthy if left in a state of rest?
“It’s a really good question,” Associate Professor Kieron Rooney, head of exercise and sport science at the University of Sydney, told me after pondering it for a while.
And, given sedentary behaviour is so unhealthy, why do humans by and large seem to prefer rest to movement?
Human as runner – and rester?
When I visit the zoo, I am often struck by the human animal’s fragility. We lack fangs, speed, even the musculature of chimpanzees.
We humans lack the musculature of our closest relative in the animal kingdom.Credit: Edwina Pickles
Evolution took a different tack with us: rather than power athletes, we are endurance specialists, says Professor Frank Marino, who studies the evolutionary biology of human performance at Charles Sturt University.
“We are incredibly efficient sweaters,” thanks to our lack of fur and lots of sweat glands, Marino tells me. Other animals cool themselves by panting, and it’s hard to run and pant at the same time. A human hunter has a range of about 15 kilometres – much further than most animals.
“In a hot environment, we can outrun almost any four-legged creature if we’re chasing them. They will stop because of heat exhaustion. We won’t,” he says.
So we were born to run? Yes – but that’s not the full story. When scientists spend time with modern hunter-gatherers, they find they are more active than city-dwellers – they do four to six hours of demanding work a day. But the rest of the day is spent pottering around camp.
Modern hunter-gatherers are much more active than city couch dwellers, yet expend roughly the same energy. Credit: Shutterstock
Harvard University paleoanthropologist Professor Daniel Lieberman uses this evidence to argue that we are adapted to both work and rest.
We evolved in an era of food scarcity. That led evolution to select behavioural adaptations that encouraged us to rest and conserve energy wherever possible, Lieberman argues. And our bodies evolved strong mechanisms to constantly trim off anything not needed.
Muscle is metabolically expensive to maintain. Without constant stimulus – lifting weights – our bodies try to strip off as much of a musculature as possible, preserving energy for other tasks. “Our muscles become weak, our bones become frail, our blood vessels can stiffen. [We need] a certain level of stress, so the body can adapt,” says Dr Jenna Taylor, an accredited exercise physiologist and lecturer at the University of Queensland.
Seen this way, chronic inactivity is harmful to our health because it is a signal for our body to start slicing away at our vital systems.
Our hunter-gatherer ancestors were simply never inactive enough, given their need to hunt for food, for this to become a big problem. Modern, sedentary humans now face the negative outcomes of that adaptation.
Rooney compares us to a wild animal that has been domesticated. “We’ve domesticated ourselves, prescribed ourselves to the capitalist culture of working 60 hours a week to earn as much money as we can to buy everything we want,” he says. “We’ve become highly stressed and far less active.”
Professor Herman Pontzer, an evolutionary anthropologist at Duke University, takes this argument further.
In a series of stunning experiments, he and colleagues showed that total energy expenditure is actually similar for active hunter-gatherers and inactive urban couch-dwellers.
If we’re using energy, but not moving, where does it go? Pontzer argues our bodies are evolved to use periods of rest between periods of activity for recovery – firing up our immune, adrenal and reproductive systems.
If we’re chronically inactive, all these systems are chronically overstimulated, which may contribute to chronic disease, Pontzer argues.
What you can do
Personal trainer Drew Westfield says everyone can do with more muscle on their body.Credit: Joe Armao
The solution? Exercise, obviously. Physical activity guidelines recommend 1¼ hours of intense activity a week, including strength training – for everyone, no matter their age.
Credit: Matt Golding
Drew Westfield, co-founder of GRIPT Gym in Melbourne, has his 65-year-old mother in the gym twice a week lifting weights as a foundation for healthy ageing.
“Everyone can do with more muscle on their body, more strength. Your joints aren’t going to be copping so much of the load because you’ve got more muscle on your skeleton to do the heavy lifting,” he says.
Westfield focuses on basic functional movements: “a squat, a hinge, a press, a pull”. For those unsure where to start, he recommends a few sessions with a personal trainer, who can develop a program and train you on how to do each exercise safely.
“By learning those fundamentals you can get comfortable in the gym by yourself,” says Westfield. “It’s a short-term investment towards someone’s long-term goal.”
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