14 March 2020 | New Scientist | 35>a special ligament to keep our head stable
when running all mean that, over long
distances, we can outrun almost any other
animal. “Thanks to our evolutionary history,
all of us have the anatomy and physiology
needed to walk and run – assuming we are not
disabled,” says Lieberman. “In today’s world,
we have medicalised, commodified and
commercialised exercise, but physical activity,
at its heart, is something we evolved to do.”
It is somewhat ironic then that many of
us today are almost entirely sedentary. The
current US and UK government guidelines
for physical activity recommend that adults
do at least 2.5 hours of moderate exercise or
75 minutes of vigorous exercise every week.
In the US, only half the population meet these
guidelines, and the situation is only slightly
better in the UK. But what counts as moderate
and vigorous exercise?
Back in the late 1980s, Bill Haskell at
Stanford University in California asked the
same question and came up with a benchmark
to compare exercise against – sitting quietly.
When seated, we expend about 1 kilocalorie
per hour for each kilogram of body mass.
Haskell and his colleagues called this a
metabolic equivalent, or 1 MET. For an
80-kilogram person, this resting metabolic
rate represents around 1920 kcals per day.Taking it easy
All physical activities can be expressed in
METs, and there is now a Compendium of
Physical Activities that contains an eclectic
mix of them described using this system. This
elegant solution to the definition of exercise
has three categories: light exercise up to
3 METs, moderate exercise between 3 and
6 METs and vigorous exercise for anything over
6 METs (see “Measuring the burn”, page 37).
Strolling, at about 2 METs, is light exercise,
while walking briskly is in the middle of
moderate at 5 METs. The transition to running
at around 7 kilometres per hour is where
exercise enters the vigorous category. A really
brisk walk and a slow run are roughly the same,
in terms of effort and calories burned. But is
this true of their health benefits too?
At first glance, it might seem that running
has the upper hand here. A study from January,
for example, was enough to make anyone sign
up for a marathon. This looked at 138 first-time
marathon runners and found that training for
and completing the 26-mile race, even at a slow
pace, is equivalent to a 4-year reduction in age
of the cardiovascular system, or even more for
those who are older and less fit.I
hated physical education at school.
Cross-country was the worst: cold,
boring and lung-burning. “Run, don’t
walk!” the teacher would shout as we jogged
reluctantly through the mud, only to walk
as soon as we were out of sight.
Over the following four decades, my PE
teacher’s angry barks have been echoed in the
constant media reports telling me that I should
run, whether informing me that jogging could
increase my lifespan by years or that training
for a marathon would make my heart younger.
The benefits of exercise are huge. If it
were a drug, it would be a miracle cure.
It keeps our hearts strong and blood vessels
supple, lessens chronic inflammation and
reduces the harmful effects of stress.
But do we need to run to get the benefits or
can we get a sufficient dose just from walking
in the limited time we have for exercise? And
what about those who warn about the toll on
joints from pounding the pavement? It is
common knowledge that running causes
arthritis and ruins the knees and hips – but
does the evidence back this up? I wanted to
find out if my PE teacher’s mantra was right.
The idea that running is the best exercise for
us – indeed, that it is part of what makes us
human – has many champions. Among them
is Daniel Lieberman at Harvard University,
who maintains that we evolved to run long
distances. He thinks that our now largely
untapped talent for persistence hunting –
chasing animals over long distances – in hot
conditions gives us an edge over other animals
and shaped our evolutionary history.
And we aren’t just good at running because
we are good at walking – in fact, technically
they are quite different (see “Mechanics of
locomotion”, page 36). A range of adaptations
such as sweat glands and hairless skin to aid
cooling, the right balance of muscle types andFeatures Cover story