It wasn't that long ago, only 10 years back, in fact, that when a woman was diagnosed with breast cancer she was told by her doctor just to go home and rest. Don't do anything strenuous. Don't lift anything over a few kilograms.

Partly this stemmed from a recognition of the rigours that chemo and other therapies wreaked on the human body. Women just didn't have the energy after chemo or surgery to do very much. But all that inactivity was taking its toll as well — on mood, on general well-being and on some specific aspects of the cancer itself, which some prescient researchers were starting to hone in on.

Among them was someone who would become a pioneer in the field, Donald McKenzie, a doctor and cancer researcher at the University of British Columbia's school of sports medicine.

McKenzie is an interesting guy, a former competitive kayaker and medical advisor to the Canadian Olympic kayaking team, and his research focus was something called lymphedema.

That's the accumulation of fluid in the upper bodies of those who have had their lymph nodes removed or radiated as part of a cancer treatment.

If strenuous exercise was extending the lives of women with breast cancer — would it also stave off the dragon for those who hadn't come down with the disease? (Kevin Frayer/Canadian Press)

McKenzie surmised that strenuous, upper-body exercise might be just the ticket for helping alleviate the fluid build-up and other problems, like restrictive lung disease, associated with it.

That was 1996. And McKenzie's cure was highly daring at the time and courageous on the part of the 24 volunteers — all breast cancer survivors ranging from age 31 to 62 — who took up the highly demanding sport of dragon-boat racing.

They began a trend for breast cancer survivors that spread nearly all over the world. They also sparked an interesting scientific challenge: If strenuous exercise was extending the lives of women with breast cancer — and McKenzie's subsequent research, and that of others, said it was — would it also stave off the dragon for those who hadn't come down with the disease?

It's early days yet, but the studies are starting to flow in and the answer seems to be a pretty convincing yes.

Indeed, according to Dr. Christine Friedenreich, a medical researcher at the Alberta Cancer Board, there have been at least 210 scientific studies in recent years trying to understand the connection between cancer and different forms of physical activity.

"On the whole," she says, "there is convincing evidence that exercise reduces the risk of acquiring colon or breast cancer by between 30 and 50 per cent." The studies also suggest that being physically active is "probably" a help in warding off lung cancer and endometrial cancer (in the lining of the womb), and "possibly" good for prostate cancer as well, she says.

"We believe we know that exercise is beneficial," she says. "The question is why and at what intensity."

The search for why

Friedenreich is one of those trying to find answers to both those questions.

Along with colleague Kerry Courneya, a phys-ed professor at the University of Alberta, she has just completed a study of more than 330 cancer-free women from Calgary and Edmonton. Between 50 and 74 years, they were put on an intensive five-day-a-week exercise program for the first time in their lives.

McKenzie's work on the dragon boaters and others concentrated mostly on fluid build-up and general well-being. Friedenreich and her team are looking for something much more exact.

The results won't be in until later this fall. The researchers are analyzing blood work from the participants and also very detailed scans of body fat trying to gauge what might be said to be exercise-induced changes in the metabolic system, insulin levels and, importantly, key hormones such as estrogen and androgen.

Breast cancer, in particular, is considered a hormonally influenced disease, which is why it strikes so many post-menopausal women whose estrogen and androgen levels tend to rise.

These hormones are produced by body fat and some studies have suggested that post-menopausal women who have gained more than 20 pounds since 18 are something like 40 per cent more likely to develop breast cancer.

The risk rate rises with the amount of adult weight that's packed on. But as exercise burns body fat, it is also lowering hormone levels and, therefore, the risk of developing breast cancer.

One of the purposes of the Friedenreich-Courneya study is to try to determine whether simply beginning an exercise program later in life can have the same effect as being physically active all along. There is some evidence to suggest it can.

The 330 or so women who participated in the Alberta trial had to be cancer free at the start of the trial. But equally important, they had to be women who were largely inactive to begin with — and were willing to throw themselves into a huge physical and time commitment, not unlike those early dragon boaters.

Each of the participants did an hour of age-related exercise a day for five days a week, three in a gym, two at home with a trainer. The adherence rate "was fantastic," says Friedenreich, virtually everyone stayed in for the long haul.

But that kind of commitment may not be needed. A year ago, researchers from Harvard Medical School reported that even moderate exercise of from three to five hours a week of walking can prolong life for those who come down with breast cancer.

Part of a follow-up of the famous Nurses' Health Study in the U.S, this one found that of 959 nurses who developed breast cancer over an 18-year period and who exercised less than three hours a week, 110 died of the disease.

Meanwhile, only 20 died of the 335 nurses who were more active.

Importantly, the results held even when accounting for smoking and eating habits — and whether the disease was diagnosed early or not.

The lesson seems pretty clear: It's never too late to put on your sneakers, grab an appropriate set of weights or, if the spirit moves you, paddle a boat.

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