When Kim Larson joined a running club and started training for her first marathon in 2005, she enjoyed plenty of support from teammates. It was her undergarments that let her down.

Larson, who wears an E cup, learned quickly that bras she had worn for tennis and other sports weren’t up to the demands of long-distance running. In addition to needing to control jiggle, she wanted extra support to prevent chafing on her shoulders and rib cage during training sessions that frequently lasted two hours or more.

“Bouncing is a big issue,” said Larson, 29. “It’s uncomfortable, plus I would really get rubbed raw.”

Breast support is not just about comfort. A good supportive bra may help protect the skin, ligaments and tissue that keep the breast from getting stretched out as a woman ages, according to Rockville plastic surgeon Gregory Dick. When these types of tissue lose their elasticity, the breasts lose their natural shapeliness and become droopy.

“Wearing a supportive bra to exercise may help minimize the damage,” he said.

A woman who wears a DD bra carries about 12 pounds of weight on her chest, which can cause back pain, a problem that often leads to the pursuit of breast-reduction surgery, Dick explains. By shifting some of that weight, the right bra may relieve that pain as well as improve posture.

Perhaps not surprisingly, good breast support is particularly important for women engaged in high-impact sports such as running.

“Breasts are made up of mostly soft, elastic tissues and don’t have much in the way of firm internal support structures to keep them from stretching and bouncing during exercise,” says LaJean Lawson, who has conducted sports bra research at the biomechanics lab at Oregon State University in Corvallis for more than 25 years. “The larger your cup size, the greater the forces on the breast and the more intense the accelerations that need to be restricted so you can exercise pain-free.”

Studies conducted by researchers at the University of Portsmouth in the United Kingdom suggest that the sometimes dramatic weight shift that comes from bouncing or swinging breasts can affect a runner’s gait and lead to injury.

“Appropriate breast support is encouraged during running to minimize breast discomfort and reduce potential injury risk,” says Jenny White, a lead author of a 2009 study published in the British journal Ergonomics.

The demand for larger-size bras in general is going up.

The most popular bra size today is 36 DD, up from a 36C in 2000, according to the Intimate Apparel Council, an industry trade group. (The difference translates roughly to two inches around the fullest part of the breast, a change widely attributed to the popularity of breast enhancement surgery and to the obesity epidemic.) Revenue from the sale of bras with cups size C or larger increased by 5.1 percent over the past year, compared with a 2.9 percent increase for all bras, according to NPD, an independent market research firm in New York.

But for larger-busted women especially, finding a properly fitting bra can be difficult. Larson resigned herself to making several visits a year from her home in Alexandria to a corsetiere in New Jersey.

“I was basically driving four hours to go bra shopping,” she said. She has since relocated to Boulder, Colo., where she opened a bra shop that caters to large-breasted women.

Bras get a lift

Compared with running shoes, which are constantly being studied and improved upon, sports bras historically have received little attention. Since the late 1970s, when two long-suffering female runners fashioned the first Jogbra from two jockstraps, the basic design has changed little.

After years playing second string to footwear, however, the humble sports bra is attracting growing interest from sportswear designers and manufacturers.

These days it is women who “are driving the growth in all sectors of sports apparel,” said John L.A. Wilson, president and chief executive of New York-based CW-X, the sports science division of Wacoal, a large Japanese lingerie maker. “The holy grail is to develop a sports bra that is supportive yet comfortable.”

Companies are offering a more diverse selection of exercise-worthy bras in a wider range of sizes. When CW-X began making sports bras in 2005, they came in just three sizes, 32 B/C, 34 B/C and 36 B/C, said Wilson. Now some styles go up to a 42DDD.

CW-X includes some unique design features in its bras. Five strips of stretchy mesh radiate from the center to the sides of each bra cup, creating a floating inner suspension system designed to reduce upward breast bounce during high-impact activities such as running and aerobics.

Moving Comfort, a Seattle-based women’s apparel company, makes 20 styles of sports bras to help “women of all shapes and sizes enjoy the benefits of exercise,” said Julie Baxter, the company’s vice president. Some styles come in sizes that fit up to a 44-inch rib cage, and designs for larger sizes are in the pipeline.

Advanced technology

Some companies rely on two- and three-dimensional imaging systems to develop and test their bras, attaching sensors to the breasts of volunteers to chart how they move during various activities.

“We pay a lot of attention to vertical breast motion, and measuring how well various bra designs tame it,” says Lawson, who is a paid consultant to Champion Athletic Wear. “It’s clearly the largest component of total breast motion during high-impact sports that require running or jumping, and the most directly related to pain and discomfort during exercise, especially for larger-breasted women.”

“Once you understand the problem and solid approaches for solving it, the actual sports bras that may result may include high-tech materials and construction techniques borrowed from athletic footwear, or they may just as effectively be made from more conventional fibers and textiles using familiar cut-and-sew techniques,” she explains.

The most notable recent change in sports bras, according to Lawson, is the attention manufacturers pay to detail, especially in larger sizes. Research she and others have amassed reveals how load is distributed throughout the bra during a workout.

Well-designed sports bras accommodate load with features such as gel-lined or seamless straps that reduce pressure and chafing. In addition, lamination techniques allow manufacturers to seamlessly layer fabrics and reinforce key areas of the bra. Companies also are increasingly choosy about materials, sometimes using two or three fabrics in a single bra “so each piece is appropriate to its use,” Lawson said.

Not everyone equates sports bra design with rocket science. Cynthia Smith, a marathon runner and triathlete in Red Bank, N.J., grew tired of wasting money on bras she permanently relegated to the back of her lingerie drawer after a single, painful test run.

She bought a used sewing machine and a book on corsetry and began designing bras based solely on her own notion of what was comfortable. She sells them under the name Lynx Sportswear online and at marathons. Lacking resources to test them scientifically, she recruits volunteers to try them on and takes notes as they jump up and down.

This spring, Lynx was selected as a 2011 finalist in the MassChallenge, a competition for entrepreneurs conducted by a Massachusetts nonprofit.

Sports stores have also gotten into the business of matching women to the right sports bra. Some of them host seminars about good fit and introduce their customers to new products.

Robyn Gault, co-owner of the Gaithersburg location of Fleet Feet Sports, routinely surprises new runners who come to her running shop for gear advice by pointing them to the bra rack.

“I tell people it’s the second most important piece of equipment they should have,” she said. (Shoes come first.)

Some scoff at the prices, which range from about $38 to $70. But once they experience the comfort of a better bra, there is usually no going back, she said.

Zeidner is a freelance writer based in Arlington.