36 | New Scientist | 17 July 2021
hugely important,” he says. Cardiovascular
fitness, muscle strength and endurance all
correlate with a lower risk of mortality, he
argues. Flexibility, not so much.
That isn’t to say that we shouldn’t aim to
maintain a healthy range of motion, and to
extend that range if necessary, says Nuzzo.
People who spend most of the day sitting and
then exercise in frantic bursts are at risk of
doing themselves an injury if they don’t take the
time to maintain a useful range of motion. But
he argues that there are better ways to achieve
this goal than a dedicated stretching regime.
“We need to get out of our minds this
notion that stretching exercise holds a
monopoly on the lengthening of tendons
and muscles,” he says. “It’s not the only activity
where flexibility or range of motion will
improve when you do it for several weeks.”
Resistance training – in particular eccentric
contractions, where muscles are loaded as they
lengthen (for example, the lowering phase of a“ There isn’t
strong evidence
that flexibility
correlates with
things that are
hugely important
for our health”
Charles Corbin and Larry Noble, then at Kansas
State University, first made the case for its
importance in overall health. They argued that
flexibility was important to maintain posture
and protect the back, while allowing the body
“freedom to move”. Soon afterwards, the sit-
and-reach test was incorporated into the first
version of US standardised physical fitness
tests as a measure of flexibility, and the idea
that stretching is the way to improve flexibility
became entrenched in the popular
consciousness. However, in his 2020 paper
“The case for retiring flexibility as a major
component of physical fitness”, Nuzzo, then
at the University of New South Wales in
Australia, argues that, while maintaining
a healthy range of motion is important,
stretching has a reputation that far outstrips
what it can actually do for our physical fitness.
For a start, the degree of flexibility you need
very much depends on what you plan to do
with your body. Normal human movement
only requires the hips to be sufficiently flexible
to allow the legs to extend backwards to an
angle of 30 degrees from upright. In other
words, for everyday activities, you only really
need the flexibility to get halfway to the splits,
at most, and there is little reason to push your
hips any further.Bending to extremes
What’s more, the kind of extreme flexibility
that makes a great social media post can be
more trouble than it is worth. As many as 20 per
cent of people have hypermobile joints, which
extend further than the normal range. This can
lead to physical problems, such as joint pain
and dislocations, if the joint hasn’t been
strengthened throughout its full range. Most
cases of joint hypermobility are inherited,
caused by an unusually loose form of collagen,
but some researchers think that certain types
of extreme stretching – dance training, for
example – can lead to joint hypermobility
and the problems this can cause. This suggests
that a training regime with flexibility as its
sole aim may not be such a good idea.
Nuzzo’s main problem with stretching,
though, is that for our overall health, it’s largely
a waste of time. “There is not strong evidence
that flexibility really correlates with a lot that’s