They say exercise such as weight training works just as well as running on a treadmill or riding an exercise bike when it comes to the long-term control of blood sugar.

A combination of both aerobic and resistance training lowered blood sugar levels better than either alone, say the researchers and both are safe.

The World Health Organization says at least 194 million people worldwide have diabetes, and that figure is expected to rise to more than 300 million by the year 2025.

The majority of people have type-2 diabetes which is usually the result of a combination of factors such as genetic predisposition, lack of exercise and an unhealthy diet.

Experts believe that the type of exercise which raises the heart beat and makes people breathe a little heavily will reduce the risk of type-2 diabetes and improve the body's control of sugar.

But there have been some doubts about the safety and effectiveness of weight training.

In a study conducted by Dr. Ronald Sigal of Calgary University, Ottawa and his colleagues, 251 people with type-2 diabetes aged 39 to 70 who had never exercised regularly were assigned them to one of four groups.

One group did 45 minutes of aerobic training three times a week; another did the same amount of resistance training; another group did both, for a total of an hour and a half of exercise three days a week, while a fourth group did no extra exercise.

The exercisers used treadmills or exercise bikes, or weight machines, at a local health club and it was found that the volunteers liked the exercise and stayed with it.

Dr. Sigal says even among the medical profession there is widespread cynicism that people will follow an exercise programme.

They participants were given a diet to follow that should have prevented any weight loss, and then their blood sugar, cholesterol, weight and other vital statistics were measured.

It was found that blood sugar levels fell with exercise and most importantly, hemoglobin A1c, which measures the blood sugar average for the past 6 months, fell by half a point on average in the people who did one form of exercise and a full point in those who did both.

The combined aerobic and weight training group experienced a 0.97 percentage point absolute drop in A1c value compared to the non-exercising group.

The aerobic training group experienced a smaller but still significant absolute drop of about 0.5 percentage point and the weight training group saw an absolute drop of about 0.5 percentage point as well.

The researchers say A1c should be between 4 and 6 but the patients started out with A1c values ranging from 6.6 to 9.9.

A drop of one point in A1c is associated with a 15 percent to 20 percent decrease in major cardiovascular events such as heart attack or stroke and a 37 percent reduction in complications such as kidney, eyes and limb damage.

Dr. Sigal says some were able to bring their A1c into the normal range, and some were also able to lower their doses of medications, and many lost weight and body fat.

The researchers say doctors should prescribe exercise to every diabetes patient as part of standard treatment.

The study is published in the current issue of the Annals of Internal Medicine.