Breast cancer survivors have been told for years that lifting anything heavy could worsen painful arm swelling. New research suggests just the opposite is true.

The study found that slowly building strength with upper-body weightlifting actually helps relieve some of the arm and hand swelling that affects up to a quarter of breast cancer survivors.

Women who have had radiation to the armpit, or who have had lymph nodes removed to check for cancer, can suffer lymphedema, a buildup of fluids that causes painful swelling of the arms or hands. The symptoms arise because the body uses lymph glands to help drain fluid.

Doctors have typically advised women to avoid using the affected arm to lift anything heavier than 15 pounds or so (6.8 kg), for fear of making the condition worse.

But in a study published this week in the New England Journal of Medicine, Kathryn Schmitz of the University of Pennsylvania School of Medicine found that women who did a twice weekly weightlifting workout while wearing a compression garment had less arm pain and swelling.

The study involved 141 breast cancer survivors who had suffered lymphedema -- some of them for as long as 15 years. Half were told not to change their exercise habits. The rest were given 90-minute weightlifting classes twice a week for 13 weeks at community gyms, mostly YMCAs.

They wore a custom-fitted compression garment on the affected arm and gradually worked up to more challenging weights and repetitions. For the next 39 weeks, they continued these exercises on their own and the women's arms were measured monthly.

After one year, fewer weightlifters had suffered lymphedema flare-ups -- 14 per cent versus 29 per cent of the others. Weightlifters reported fewer symptoms and greater strength. Rates of change in arm size due to swelling were similar in both groups.

While 14 per cent of the 65 women who participated in the weight program saw their symptoms worsen, the rate was twice as high among the 65 women who did not do the upper body exercises.

Schmitz and her colleagues had made similar findings in a smaller study published in 2006, but this trial lasted twice as long, involved more women, and involved women who had suffered lymphedema longer.

She says she hopes her study puts the old advice to rest and encourages breast cancer survivors head to the gym.

She suggests women with lymphedema find a well-fitting compression garment and a certified fitness professional to teach them how to do the exercises properly before embarking on a weightlifting program. She also advises they start slow, with a program that gradually progresses.

Schmitz is now working on another part of the study that is evaluating whether weight training can prevent a first case of lymphedema in breast cancer survivors. Results are expected soon.