The Physics of Bras

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The Physics of Bras

Force = Mass x Acceleration

Overcoming Newton's second law with better bra

technology

By Anne Casselman

DISCOVER Vol. 26 No. 11 | November 2005

One side effect of the obesity epidemic in America is

rarely noted: Women's chests are expanding nearly as

fast as their bellies. Poor eating habits, as well as

breast implants and the estrogens in birth-control

pills, have led to an increase in the past 15 years of

more than one bra size for the average American

woman—from a 34B to a 36C. For many women, this has

been a burdensome trend. A pair of D-cup breasts

weighs between 15 and 23 pounds—the equivalent of

carrying around two small turkeys. The larger the

breasts, the more they move and the greater the

discomfort. In one study, 56 percent of women suffered

from breast pain when jogging.

" Women will limit themselves from doing exercise

because of their breasts, " says Deirdre McGhee, a

sports physiotherapist and graduate student in

biomechanics at the University of Wollongong in

Australia. " They actually deprive themselves. " GHOST

OF THE MACHINE

An x-ray scan of a bra reveals major structural

elements, including straps, fasteners, and underwires.

And the less they exercise, the more obese and buxom

they may become.

For most women, a good bra is still the best remedy.

According to the American Apparel and Footwear

Association, nearly 500 million bras were sold in the

United States in 2001; last year, sales totaled more

than $5 billion. As breasts have grown, so have the

demands of customers, the scientific sophistication of

bra design, and the competition among bra

manufacturers. " Women like their bras to be sexy and

sensual and comfy and supportive, " McGhee says. " And

to get all that is rare. " Yet after nearly a century

of experimentation, the perfect bra may well be in

sight.

Bra designers begin with a significant handicap: The

structure of breasts is still something of a mystery.

Evolutionary biologists aren't sure why breasts

evolved as they did—chimpanzees and other mammals

develop them only when lactating—and no one knows what

keeps them from sagging. An individual breast is made

up of between 15 and 20 sections, known as lobes.

These are composed of smaller lobules that end in

bulbs that produce milk and are interconnected by a

network of ducts. But breasts contain no muscles at

all, and the bulbs and ducts are essentially the same

in all women. Size is mainly determined by how much

fat the breasts contain. Most anatomists believe the

breasts' primary means of support are the 's

ligaments interlaced among the lobules. But others

give the skin more credit.

To best support breasts, a designer has to understand

how they move. To that end, McGhee's team in

Australia, headed by biomechanist Steele, tags

women with light-emitting diodes and asks them to run

on treadmills. (The women run with and without bras,

so the laboratory doors are bolted to prevent

uninvited people from bursting in.) Computer systems

then track the breasts' motions in three dimensions by

following the moving lights. " We can actually work out

exactly where they're going, how they're moving, and

how this movement is affected by bras, " Steele says.

Breasts move in a sinusoidal pattern, Steele has

found, and they move a lot. Small breasts can move

more than three inches vertically during a jog, and

large breasts sometimes leave their bras entirely. " We

have videos of women who, particularly if the cup is

too low, spill all over the top, " Steele says.

The larger the breasts and the more they move, the

more momentum they generate. To change or stop that

momentum requires a large force, usually applied

through bra straps. When straps are thin, the pressure

exerted through them can be so great as to leave

furrows in the shoulders of large-breasted women. As

the straps dig into the brachial plexus, the nerve

group that runs down the arm, they may cause numbness

in the little finger. In some cases, breasts can slap

against the chest with enough force to break the

clavicle.

" Force equals mass times acceleration, " Steele says.

" That's Newton's second law. You have a large mass,

and it's going quickly, and the force is going to be

large. If you have breasts that are slapping down and

hitting the chest and having to come back up, they

accelerate very quickly. " No one really knows the

long-term medical consequences of " excessive breast

bounce, " as Steele calls it. But it can cause pain and

is the most likely reason for sagging breasts.

There are two ways to keep breasts from moving:

encapsulation and compression. Encapsulation bras look

like the old-fashioned brassieres our grandmothers

wore, with large molded cups that completely contain

the breast. Compression bras are more popular but less

comfortable: They squash the breasts against the body,

thereby reducing the amount of weight the bra has to

cantilever.

Since the 1800s, when women used corsets stiffened by

whalebone to support their breasts, bra designers have

experimented with innumerable structures and

materials. " Making a bra is like building a bridge, "

says Manette Scheininger, a senior vice president of

design, merchandising, and research and development at

Maidenform. " You have weight that has to be uplifted.

You have to have support all around. " Larger breasts

compound the challenge, Scheininger says. " And not

just by a little bit. The challenge grows

dramatically. "

The first sports bra was created in 1977, when two

American women took a pair of jockstraps, cut them

apart, and sewed them back together. They dubbed their

creation the Jogbra. Other bra designs since then have

used gel and water pads, silver fibers that cool the

skin and dispel bacterial growth and body odor, and

air bags that wearers can pump up to enhance the

appearance of their breasts. This past summer, a

virtually stitchless bra was introduced by Wacoal, a

leading manufacturer. The bra is molded, compressed,

and shaped at the same time— " sort of like a car

fender, " Wacoal designer Hyde says. Thanks to

cylindrical hosiery machines, other bras can now be

knit in circular patterns with differing amounts of

stretch and support.

To track the motions of women's breasts and find

better ways to support them, biomechanists in

Austrailia fit subjects with specially designed bras.

In back, sensors are placed under the straps to

measure how much pressure they exert on the shoulders,

and electrodes are placed on the upper torso and the

neck to monitor the bra's effects on muscle activity.

Small, light-emitting diodes are placed in front of

the sternum, nipples, and bra cups to measure the

subject's breast and torso movements.

Steele's team is taking fabric technology another

step. Six years ago, her laboratory, in collaboration

with the University of Wollongong's Intelligent

Polymer Research Institute, began work on the world's

first smart bra. It uses intelligent materials and

electronic textiles to sense when breast motion

increases and tighten appropriate parts of the bra in

response. " When you're sitting around the office, it

isn't restrictive, " Steele says. " But if you need to

run for a bus or something, it will sense that you've

started to run, and it will give you the support of a

sports bra. " Steele's lab has teamed up with Marks &

Spencer, a major retailer in Britain, to further

develop the project.

Meanwhile, McGhee and Steele have their sights set

beyond tinkering with bra straps and fabrics. They are

using Steele's extensive work on the biomechanics of

breasts to explore an entirely new way of designing

bras. Starting in the 1970s, podiatrists and

biomechanists radically redesigned running shoes to

make them lighter and more stable. Steele and McGhee

hope to accomplish a similar paradigm shift and

correct the problem with the most supportive bras:

They are also rated the most uncomfortable. " We're not

testing a product but a concept, " says Steele. " What

we're trying to bring in now is an idea that will not

be a gimmick—understanding the structure, function,

and the movement and putting them all together with

the science underpinning it. "

New York socialite Phelps is often

credited with inventing the bra in 1914, but the first

patent for a breast supporter was granted half a

century earlier to Luman. L. Chapman of Camden, New

Jersey. Bra manufacturer S.H. Camp and Company first

matched breast sizes to the letters of the alphabet, A

through D, in 1933.

Steele and McGhee are reluctant to divulge any details

for fear of tipping off rival designers— " It's a really

dirty game, " McGhee says. But initial trials are under

way while they stake out intellectual property rights.

Given that more than 30 percent of American women now

wear D cups and larger, the team shouldn't have

trouble finding a commercial partner if they succeed.

When it comes to bras, the usual rules of exercise are

reversed: No pain, very much gain.