THURSDAY, March 6 (HealthDay News) -- The thousands of Americans who undergo knee replacement surgeries each year may want to put away their tennis rackets and get back on their bikes, a new study shows.

Biking and treadmill walking appear to be two of the gentlest exercises for those who have had a knee replaced with an artificial joint, researchers found, while higher impact sports such as jogging and tennis generated higher forces on new knees, according to study author Dr. Darryl D'Lima, director of the Orthopaedic Research Laboratory at Scripps Clinic, in La Jolla, Calif.

More surprisingly, golf swings were also tough on the knees, although D'Lima was quick to point out the swings make up just part of the exercise in a round of golf.

He is scheduled to present his research Thursday at the American Academy of Orthopaedic Surgeon's annual meeting in San Francisco. The study was initiated by Dr. Clifford W. Colwell, director of the Shiley Center for Orthopaedic Research & Education at Scripps.

An estimated 478,000 total knee replacement surgeries, called total knee arthoplasties (TKAs), are done in the United States each year, according to the researchers. In the surgery, the original joint is replaced by one made of various materials, such as plastic and metal.

Surgeons typically advise patients to resume physical activity when they are able. But advice about which activity is best has been subjective, D'Lima said. So, his team decided to measure forces on the knee while patients took part in a variety of exercises.

In the study, D'Lima's team measured forces on the tibia, or shinbone, in four patients who had undergone TKA. These four patients had a specially designed joint that allowed forces to be measured from inside the implant.

A year after their surgery, each of the four patients jogged, played tennis, did golf swings, walked (on a treadmill and on level ground) and biked while the forces to their knee area were measured.

Golf swings produced forces of 4.5 times body weight on the forward knee and 3.2 times body weight in the opposite knee, the researchers found.

D'Lima noted that the forces produced by the golf swing, however, occur in an instant, while the forces produced by jogging are constant. "I think golf should be OK," he said. "It's more of scientific interest."

There were some other surprises, D'Lima said. "We expected that walking on a treadmill, which is more controlled, would be better than biking [in terms of low impact to the knee]," the researcher noted. But biking actually won out, he said.

Other details on the results:

• Biking generated the least force, producing impact of about 1.3 times the person's body weight.
• Treadmill walking was next best, producing forces of 2.05 the body weight.
• Walking on level ground generated forces of 2.6 times the body weight.
• Tennis produced forces of 3.1 to 3.8 times the body weight, with serving producing the highest impact.
• Jogging produced forces of 4.3 times body weight.

Modification of certain high-impact exercises could help, he said. For avid golfers, "it's possible you could modify your swing," D'Lima says. Golfers could get a high-tech evaluation of their swings, offered by many golf club makers, or ask their pro about modifying the swing to exert less force on their knee, D'Lima suggested.

However, for more strenuous high-impact pursuits such as jogging, people who've undergone knee replacement should make a permanent switch to another form of exercise, the expert said.

Dr. Daniel Oakes, a staff orthopedic surgeon at Santa Monica-UCLA & Orthopaedic Hospital in Santa Monica, Calif., said the study confirms advice he generally gives to his knee-replacement patients.

"We strongly dissuade [them from] jogging," he said. "I tell them activities that are OK are walking, biking, hiking, riding an exercise bike, riding an elliptical trainer and walking on the treadmill."

He suggests doubles tennis, not singles, since it is not as aggressive. He generally allows downhill or cross-country skiers to resume that sport when they are healed. And he thinks golf is fine.

While the study confirms the experts' suspicions about which activities are more stressful on the new knee, it can't be determined from the study if the increased forces will lead to a higher failure rate in the joint, said Oakes, who is also an assistant professor of orthopedic surgery and chief of the joint replacement service at the University of California Los Angeles' David Geffen School of Medicine.

More information

To learn more about knee replacement, visit the American Academy of Orthopaedic Surgeon.

FRIDAY, Feb. 29 (HealthDay News) -- There may be a link between rising rates of carbohydrate intake and obesity and the increasing number of esophageal cancer cases in the United States, a new study says.

Researchers noted that cases of esophageal cancer increased from 300,000 in 1973 to 2.1 million in 2001, which closely mirrors increases in carbohydrate intake and obesity over the same time.

Obesity is a major risk factor for many types of cancer, and a diet high in calories from refined carbohydrates is a common contributor to obesity, the researchers noted. They also said no other studied nutrients were found to correlate with esophageal cancer rates.

"If we can reverse the trends in refined carbohydrate intake and obesity in the U.S., we may be able to reduce the incidence of esophageal cancer," study senior author Dr. Li Li, an assistant professor in the department of family medicine and the Case Comprehensive Cancer Center at Case Western Reserve University/University Hospitals Health System, said in a prepared statement.

The study was published in a recent issue of The American Journal of Gastroenterology.

The causes of esophageal cancer are largely unknown, and despite recent advances, patients with this type of cancer have a poor prognosis. The five-year survival rate is less than 20 percent.

More information

The American Cancer Society has more about esophageal cancer  .

THURSDAY, Feb. 21 (HealthDay News) -- A moderate level of aerobic fitness can significantly reduce stroke risk in men and women, according to a large, long-running study.

The study, expected to be presented Thursday at the American Stroke Association's International Stroke Conference in New Orleans, showed 30 minutes or more of brisk walking, or an equivalent aerobic activity, five days a week could lower stroke risk by about 40 percent.

Fitness has a protective effect regardless of the presence or absence of other stroke risk factors, including family history of cardiovascular disease, diabetes, high blood pressure, elevated cholesterol levels and high body mass index, study author Steven Hooker said in a prepared statement.

This study is the first to suggest there may be a significant independent association between cardiorespiratory fitness (CRF) and fatal and nonfatal stroke in men and nonfatal stroke in women, said Hooker, director of the Prevention Research Center at the University of South Carolina Arnold School of Public Health.

About 780,000 U.S. adults suffer a stroke each year, and stroke is a leading cause of serious, long-term disability in the United States, according to the American Stroke Association. About 150,000 people die from strokes annually, making it the nation's No. 3 cause of death.

Researchers analyzed data on more than 60,000 people -- 46,405 men and 15,282 women -- who participated in a long-term study at the Cooper Aerobics Center in Dallas between 1970 and 2001. The participants, aged 18 to 100 and free of known cardiovascular disease when they entered the study, were followed for an average of 18 years. During that time, 863 people -- 692 men and 171 women -- had strokes.

Upon entering the study, each participant took a test to measure cardiorespiratory fitness in which they walked on a treadmill at an increasing grade and/or speed until they reached their maximal aerobic capacity.

Men in the highest quartile (25 percent) of CRF had a 40 percent lower relative risk of stroke compared with men in the lowest quartile. That difference stayed constant even after adjusting for other factors such as smoking, alcohol intake, family history of cardiovascular disease, body-mass index (an estimation of body fatness), high blood pressure, diabetes and high cholesterol levels, Hooker said.

Among women, those with a higher cardiorespiratory fitness level had a 43 percent lower relative risk than those in the lowest fitness level.

The overall stroke risk dropped substantially at the moderate CRF level, with the protective effect persisting almost unchanged through higher fitness levels.

"We found that a low-to-moderate amount of aerobic fitness for men and women across the whole adult age spectrum would be enough to substantially reduce stroke risk," Hooker said.

Physical activity is a major modifiable cardiovascular disease risk factor. Increasing the nation's CRF through regular physical activity could be a vital weapon to lower the incidence of stroke in men and women, he said.

One of the study's limitations is that most of the participants were white, well-educated and middle-upper income, Hooker said. He recommended that data be collected from other populations.

More information

To learn more about improving your cardiovascular fitness level, visit the American Heart Association  .

THURSDAY, Feb. 21 (HealthDay News) -- Fish oil won't help prevent a stroke, but a high-fiber diet might make a difference, say two new studies designed to assess the impact of nutrition on stroke.

"Fish oils are not as good as people claim them to be," said Dr. Craig Anderson, lead author of the fish oil study and director of the neurological and mental health division at the George Institute for International Health at the University of Sydney, in Australia.

On the other hand, "eating 20 to 35 grams of fiber per day may reduce the risk of stroke and may result in better outcomes if you do have a stroke," said Angela Besanger, lead author of the fiber study and a nutritionist at Massachusetts General Hospital in Boston.

Both studies were expected to be presented Thursday at the American Stroke Association's International Stroke Conference in New Orleans.

Every year, more than 700,000 Americans have a stroke, according to the National Institute of Neurological Disorders and Stroke (NINDS). Stroke is the third-leading killer in the United States and is the leading cause of disability.

Known risk factors for stroke include cigarette smoking, high blood pressure, heart disease and diabetes. Past research has suggested that fish oil -- either directly from fish or from supplements -- could improve cardiovascular health and possibly decrease the risk of stroke.

To assess whether or not fish oil truly has an impact on stroke risk, the Australian researchers randomized 102 people who'd had a stroke to take either a daily fish oil supplement or a placebo for 12 weeks.

They found no evidence of benefit on markers of cardiovascular risk in people taking fish oil supplements when compared to the placebo group.

"From our research and on the basis of other data, I do not recommend low-medium doses of fish oil to my patients. Conversely, though, I do not discourage them if they personally wish to take the treatment as it might encourage other lifestyle changes," Anderson said.

The fiber study, which Besanger said is the first of its kind, included 50 people who'd just had a stroke. The researchers asked them to recall everything they'd eaten within 24 hours of having a stroke and compared that information to their disability level and general health at six months.

They found that those with the highest levels of fiber intake had better outcomes, but study co-author Dr. Karen Furie, director of the stroke service at Massachusetts General, pointed out that "this wasn't a clinical trial. We didn't give people fiber. The association was pretty dramatic, but this was a small sample size, and it's only observational data. These findings need to be replicated in a larger study."

However, Furie also noted that a recommendation to increase the amount of fiber in your diet is "a recommendation that's pretty easy to endorse. There are no downsides to increasing fiber intake."

"People attracted to these ideas [more fiber and fish oil] could be healthier to begin with," said Dr. Keith Siller, an assistant professor of neurology at New York University Medical Center in New York City. "It's very hard to validate whether taking fiber or fish oil has a direct effect on stroke risk. They're probably more a marker of people that live a healthier lifestyle."

More information

To learn more about stroke and how to prevent one, visit the National Institute of Neurological Disorders and Stroke.