2020-03-14_New_Scientist

14 March 2020 | New Scientist | 37

The idea that running wears the body out

is a myth, says Lieberman. “In fact, quite the

reverse. Running helps activate all kinds of

repair and maintenance mechanisms,” he says.

But it is possible to overdo it. A 2017 meta-

analysis including more than 125,000 people

found that 3.5 per cent of recreational runners

had osteoarthritis in the hip or knee compared

with 10 per cent of sedentary non-runners.

Yet 13 per cent of elite runners who had taken

part in international competitions had such

osteoarthritis. For recreational runners at

least, it seems there is a sweet spot at which

running protects against osteoarthritis.

That is good news for most joggers, but

what about the risk of strains and sprains?

“Running, like everything, however, has

trade-offs including greater risk of injury,”

says Lieberman.

When it comes to injuries such as sprains,

walking beats running hands down. A study

of the exercise habits of more than 14,000

Spanish graduates, for instance, found walking

resulted in 40 per cent fewer injuries than

running for equal energy expended. The injury

rate of running was less than that of football,

sailing and martial arts, and similar to that of

skiing and tennis.

The risk of injuries from running depends on

factors such as how long you have been doing it,

as well as your age and sex. A 2015 meta-analysis

of 13 studies of running-related injuries found

that novice runners were most likely to get

SOURCE: COMPENDIUM OF PHYSICAL ACTIVITIES

MODERATE EXERCISE

LIGHT EXERCISE

Running up stairs

Swimming (fast crawl 4 km/h)

Metabolic equivalents (METs)

Speed (km/h)

0246810121416

Cycling (20 km/h)

Vacuuming

Sex

RESTING RATE

Soccer

Downhill skiing

Rowing (over 9 km/h)

Swimming (butterfly)

RUNNING

WALKING

16

14

12

10

8

6

4

2

0

were scanned in detail six months before the

race and again a few weeks after. The scans

revealed that the knee’s main weight-bearing

compartments – the parts most likely to

develop arthritis in the long term – had

become stronger as a result of the marathon

training. “It was a very big surprise,” says Hart.

The kneecap part of the joint, however, did

show damage, but follow-up scans revealed

that this had reversed six months later, when

the participants had reverted to less intense

running regimes. Hart’s take-home message

is “distance running can have long-term

benefits for your knees”. The team also did a

study on hips, which found that 560 kilometres

of a marathon training programme, ending in

the race, didn’t cause pre-arthritic changes in

the hip joint. “Our findings suggest that the

high impact forces during marathon running

were well tolerated by the hip joint,” says Horga.

Wear and tear

Another treasure trove of data on wear and

tear comes from the National Walkers’ and

National Runners’ health studies. As part

of this, Williams looked at osteoarthritis,

which is caused by the breakdown of bones

or cartilage in joints. He found that doing

more running or walking actually reduced

the risk of osteoarthritis and the need for hip

replacements. It didn’t seem to matter if the

participants walked briskly or ran slowly.

says Brellenthin. “There may be additional
benefits of running, particularly for
cardiovascular health, related to the higher
intensity of running. However, intensity is
relative to individual fitness levels, and a brisk
walk will provide numerous health benefits for
people like beginners and older adults.”
This is great news for joggers and hikers, but
not if our body gets worn out or injured in the
process. Could this risk outweigh the benefits?
There is no doubt that running is a high-
impact activity. When the foot hits the ground,
a force equivalent to two or three times your
body weight pushes up through the body.
Bones, joints, muscles and ligaments must
absorb this force. The question is whether this
wears your joints out, as many of us believe.
As I get older, this is something I worry
about. I’m not alone. “Most people understand
that exercise is good for you, that it is good for
the cardiovascular system, but at what expense,
if you’ve worn your knees out in the process?”
says Alister Hart, a surgeon at the Royal
National Orthopaedic Hospital in London. This
question was on his mind back in 2012, when
he was hobbling around after completing his
first marathon, so he decided to study the
impact of marathon running on knees.
Together with his colleague Laura Maria
Horga and others, he recruited 82 runners
taking part in the London marathon, all of
whom were over 40 and had never run this
distance before. Using MRI, the runners’ knees

50

40

30

20

10

0 SOURCE: doi.org/f2tcr3

Survival of the fittest

Even a small amount of exercise boosts health, but this

effect tapers off with increasing time spent exercising

Running

(vigorous intensity

exercise)

Reduction in risk of dying compared

with inactive individuals (%)

0 20406080100

Walking

(moderate intensity

exercise)

Duration (minutes/day)

A 5-minute run generates the same benefits as a

15-minute walk, and a 25-minute run is equivalent

to a 105-minute walk

Measuring the burn

The energy expended during exercise can be measured in metabolic equivalents (METs),
where 1 MET is the metabolic rate at rest. Walking counts as vigorous exercise, if you go fast enough

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