15 June 2019 | New Scientist | 35feel-good drugs – in response to endurance
exercise. The “runner’s high” was born,
taking up residence in our brains alongside
our ancient, simian desire to rest. These two
competing drives were balanced by a lifestyle
that demanded hard work, but rewarded
strategic laziness.
These sirens continue to call from opposite
shores inside our evolved minds, luring us
towards idleness or action. But recently, and
in the blink of an evolutionary eye, our
environment has changed. In the well-stocked
human zoos many of us now inhabit, we have
largely engineered away hunger, fear and the
other demons that got our hunter-gatherer
ancestors moving. We have made it easy to
overindulge, leading to heart disease, obesity,
diabetes and other plagues of civilisation.
In our Palaeolithic past, we could know what
our bodies needed by listening to what they
wanted. In the modern world, relying on our
neural reward systems to deliver the proper
dose of exercise feels a bit like trusting my
4-year-old daughter to serve herself healthy
portions of broccoli and ice cream.The perils of sloth
Our strange modern environment has
also exposed our seemingly paradoxical
relationship with exercise. Some of us,
like Dom and other ultramarathon
competitors, seek it out in large doses,
feeding the evolved craving for physical
activity. Yet, mostly we avoid it. Our lazy
inner ape calls the shots far too often.
The health benefits of exercise and the perils
of sloth have long been known. Even Socrates,
not remembered as an athlete, bemoaned
the lack of fitness among his students. Today,
many people would like to be more active
to improve their health. But how much
more? To get a better sense of the amount of
exercise we should be aiming for, we need to
understand exactly what it does to our bodies.
It has taken a surprisingly long time to figure
that out, but recent work is illuminating.
First, the obvious benefits: exercise keeps
our muscles and hearts strong, our blood
vessels pliant and improves aerobic fitness.
When we get our heart rate up, the stresses
imposed by the blood rushing through our
arteries promotes the production of nitric
oxide, which helps repair blood vessels and
keep them elastic. Maintaining strength and
aerobic fitness is particularly important asT
HE Spine Challenger is a brutal race.
It claws its way along the toughest
174 kilometres of the Pennines, the
geological backbone of England, in the dead
of winter. It must be completed in 60 hours.
Finishers rack up some 5400 metres of ascent,
equivalent to climbing Mont Blanc twice.
Participants in 2017 – the fast ones,
anyway – would have glimpsed Dom Layfield,
an irrepressibly upbeat man in his 40s,
pulling away and disappearing into the
low clouds and sleet. They let him go,
perhaps thinking that this first-timer had
underestimated the race’s difficulty and
would burn out. They were wrong. After
28 hours of non-stop running and scrambling,
he finished first, an hour ahead of his nearest
rival, setting a course record.
If exercise is medicine – as we are often
told – surely the Spine Challenger is a massive
overdose. To complete it takes more than
20 times the 10,000 steps that many of us
aspire to each day. Yet hundreds of these
ultramarathons have sprung up around the
world, and the most prestigious have to
turn eager contestants away. At the same
time, lifts and escalators are jammed with
people who would never consider climbing
the stairs. In fact, the average person in the
US takes fewer than 5000 steps a day and in
the UK it isn’t much more.As a species, we have a love-hate relationship
with exercise. Many people fail to get enough,
some seem to get too much. So, what is the
correct dose? Or, put another way for the Fitbit
generation: how many daily steps should we
take to make the most of this marvellous
medicine?
Dom and I met as PhD students in 2001,
dissecting cadavers at Harvard Medical School.
Chatting as we worked, we discovered a shared
love of the mountains. A friendship was born
amid the grease and formalin. In the years
since, we have spent many happy days
climbing, skiing and running together. The
one constant has been Dom pulling ahead,
wearing me out. So I have a sense of how the
other racers in the Spine Challenger must have
felt. As a scientist working at the intersection
of human evolution, energetics and health,
I also find myself wondering what our species’
immense capacity for physical exertion tells
us about the way our bodies are built.
We evolved from lazy stock. All animals
rest when they can, saving precious calories
for survival and reproduction, but by any
measure, our great ape relatives are
impressively sedentary, resting and sleeping
for 18 hours a day. However, when our
ancestors began hunting and gathering,
around 2.5 million years ago, it put an
evolutionary premium on physical exertion.
These activities are incredibly demanding,
requiring hours of effort each day to find food.
Individuals that were more active found more
food and had more offspring – and these, in
turn, inherited their desire to move. Over
generations, the human brain evolved to
reward hard work, releasing endorphins and
endocannabinoids – the body’s homemade,>“ Mostly we avoid exercise. Our lazy
inner ape calls the shots far too often”