WASHINGTON (AP) _ Stopping at the health club to lift weights may help you to go farther on your bike, experts say.

Strength training, which is supposed to build short-term power, also stretches endurance, apparently by pushing off the point at which muscles build up lactic acid, an exercise byproduct that causes fatigue, researchers say.

''I think we found something that could be applied by athletes and that's not often the case'' in investigative studies, said physiologist Edward J. Marcinik of the Naval Medical Research Institute, Bethesda, Md. He did the research for his doctorate at the University of Maryland.

Marcinik and his colleagues looked at 10 men between 25 and 34 years of age who did three circuits of 10 upper and lower body exercises on resistance machines three times a week for 12 weeks.

An instructor supervised them as they did eight-to-12 repetitions on arm and shoulder exercises and 15-20 on the others, which focused on the hips, knees and legs. A 30-second rest was allowed between exercises, and the weights were increased as the men got stronger.

The program was strenuous, but not ''not atypical'' for serious exercisers in that age group, said Ben Hurley, an associate professor at the University of Maryland who worked with Marcinik. Three trips around the weight circuit is generally recommended in scientific literature for peak strength gains, he said.

''We tried to make it a typical kind that someone who joins a health club would typically do,'' Hurley said.

The exercisers were forbidden to do aerobic training such as running or cycling, because those sports are known to increase endurance. The men were endurance tested on stationary bikes before and after the training.

After training, the men could cycle an average of 33 percent (8.8 minutes) longer before they fell below a minimum work intensity set by the researchers.

Another way to look at this is to say the men could go farther before hitting their lactate threshold, the point at which lactic acid production surges, according to the report in the American College of Sports Medicine journal, Medicine and Science in Sports and Exercise.

It's not clear why weight training would improve endurance, but the weight workouts might teach muscles to exercise more efficiently, using fibers that produce less lactic acid, Hurley said.

Also, leg movements involved in weight training may be similar enough to cycling movements to produce a crossover effect, Marcinik said. For instance, cyclists push down with fairly constant force on the pedals, as weight trainers do when doing a leg press, he said.

Besides the endurance gains, weight workouts produced leg strength gains of 30-35 percent, the study says.

And, although cycling is an endurance sport, strength is very important. On a bike, your legs are likely to give out before you reach your maximal aerobic capacity, a limit of your body's ability to feed oxygen to your muscles, Marcinik said.

Weight training may have less benefit for runners, because aerobic capacity is more likely than leg strength to set the limits of their endurance, Marcinik said. But some research has indicated weights could help runners, too, he said.

Some people may undervalue weight training as an endurance exercise because it doesn't improve aerobic capacity, Hurley said.

But the study shows that maximal aerobic capacity is no perfect measure of endurance, Hurley said. Even though the weight trainers did not significantly improve their aerobic capacity, they still lasted longer on the cycles, the researcher said.

And, when they exercised at set percentages of their aerobic maximum, their lactic acid levels were significantly lower after weight training, he said.

''What it says is that the body is being stressed less at each of these workloads,'' Hurley said.

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