54 | New Scientist | 15 June 2019
Swim for it
My preferred form of exercise is
swimming. For a given distance,
which stroke is the best to use in
terms of calories burned?Millie Hughes
Amersham, Buckinghamshire, UK
The best stroke for burning
calories is butterfly, but it isn’t
sustainable over longer distances.
The breaststroke is the next best,
followed by front crawl and
then backstroke.
Swimming is a particularly
good way of burning calories
if you have problems with your
joints, such as the knees or hips,
as it is a very low impact activity.Ann Smith
Canberra, ACT, Australia
Breaststroke was probably the
earliest known stroke, as it was
depicted 8000 years ago in
paintings in the so-called Cave
of Swimmers in the Gilf Kebir
plateau, Egypt. It is also the least
efficient stroke and is relatively
slow, but it is a very comfortable
way to swim.
Butterfly is the most recently
developed stroke, first used
in competition in 1933. It is
a little more efficient than
breaststroke, but is considerably
faster because the overhead arm
return reduces water drag.
Front crawl is the fastest.
This is because it uses a body roll
and out-of-water arm return, that
reduce drag at the shoulder. It also
uses a kick that further minimises
drag by keeping the legs behind
the body. Versions of this stroke
can be seen in ancient Egyptian art
from around 4000 years ago. The
efficiency of front crawl is relatively
high, and in “freestyle” events,
where swimmers can choose their
stroke, they inevitably choose the
front crawl. Indeed, many people
now think that freestyle is the
name of that stroke style.
So, for maximum energy
usage over a given distance,
swim fast and choose butterfly
or breaststroke. But bear in mind
that the efficiency of propulsiondrops and energy expenditure
increases with age. However, be
aware of the various articles in
New Scientist (including this issue,
page 34) that note a rapid fall-off
in energy expenditure above a
modest initial level of exercise.
In practice, it may not matter
much which stroke you use to
lose weight.Stephen Johnson (US Masters
swimming world record holder,
800 metre relay) Eugene,
Oregon, US
How many calories are used
depends on factors including an
individual’s resting metabolic rate,
their weight and whether they
are swimming quickly or slowly.
Since butterfly requires the
body to be partially lifted out
of the water, as well as a strong,
well-timed set of kicks, it is
almost never swum for more
than 200 metres, even by
world-class swimmers. Most
people swimming for fitness
choose freestyle, and theyshould remember to use their
legs in a steady fashion.Virginia Trimble
Irvine, California, US
My expertise on this topic goes
back about 60 years, but then, it
was certainly the butterfly that left
me the most breathless. I conclude
that this stroke burns the most
fuel per minute and per metre.Patrick Anderson
Canberra, ACT, Australia
A good way to burn calories in a
small pool is to run on the spot at
a point in the water between waist
and neck deep. For a more intense
workout, grasp an edge or corner
of the pool, extend your legs
horizontally and kick. Alternating
speeds can then achieve a leisurely
or aerobic calorie burn.Spots or stripes
Why do some animals have
patterns of hair colours such
as stripes or spots, and why
can’t I have stripy hair?David Muir
Edinburgh, UK
Whether an animal has spots,
stripes or neither depends on
the size of the embryo when two
types of melanin form on its skin:
eumelanin, which gives dark hair
when abundant or light when not,
and pheomelanin, which gives red
hair when abundant. The patterns
depend on a chemical process
called a reaction-diffusion model,
first hypothesised by Alan Turing
in the 1950s.
If the embryo is very small,
no pattern forms. If slightly bigger,
the pattern is striped. If bigger still,
it is spotted. If even bigger, there is
again no pattern. Shape also plays
a role: if part of the embryo of a
potentially spotted animal is
elongated, that part can become
striped. This is why a spotted
cheetah has a stripy tail, and
why there is no striped animal
with a spotted tail.Mike Follows
Sutton Coldfield, West Midlands, UK
It would appear that there is no
evolutionary advantage to having
patterned hair in humans, though
some, like the late Dickie Davis
have a Mallen streak, a section
of white or lighter hair caused
by hereditary poliosis. Blaschko’s
lines, which can be seen on skin
under UV light, may hint that
our ancestors had patterned
body hair. After all, many men
have patterned beards in colours
that are distinct from the hair
on their heads. ❚This week’s new questions
A few years ago, I was bitten on the hand by a red-bellied
black snake. After a night in intensive care (during which
I was not given antivenom), I soon recovered, with one
exception: the complete loss of my sense of smell. How
can a bite on the hand do this and could it affect other
senses? Tony Blake, Adelaide, South AustraliaWhy do we experience a cold sensation in our mouth or
nose when eating or inhaling menthol? Tegan Edwards,
Ipswich, Suffolk, UKWant to send us a question or answer?
Email us at [email protected]
Questions should be about everyday science phenomena
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KEN^ GRIFFITHSALAMYHow can snake venom
knock out your sense
of smell?