Here's good news for geezers — or for merely middle-aged folks — who'd like to stay fit and independent far into their later years.

You don't have to lift heavy weights to build muscle strength. Lifting lighter weights can be just as effective if you do it right, and you're much less likely to hurt yourself, researchers say.

That's important information for people exercise expert Stuart Phillips calls "mere mortals" — those with dwindling muscle mass who want stay active, as distinct from body-builders and elite athletes.

Phillips, a professor of kinesthesiology at McMaster University in Ontario, says everybody needs to do some kind of resistance training to build muscle strength as they age. Cardiovascular exercise, while important, isn't enough to maintain muscle mass.

"For most people that's meant going to the gym and lifting heavy weights," Phillips told Shots. That's mainly because of the hoary dogma that to build muscle you've got to lift 80 percent of your all-out maximum weight for eight to 10 reps.

"But that's kind of a daunting thought for most people," Philips said. And he and his colleagues suspected the dogma wasn't the whole story. In earlier studies they looked at what goes on inside muscles after conventional 80-percent-of-maximum, low-rep lifting versus hefting 30 percent of maximum weight until the muscle becomes too fatigued to go on. That's usually around 25 to 30 reps.

They found that both approaches produced the same amount of new protein.

So they took a group of 21-year-old men who were weight lifting novices. Three times a week, they had them do knee extensions on a weight machine. That isolates and strengthens the quadriceps muscles on the front of the thigh. "Those are the most important muscles for standing up and getting out of a chair," Phillips points out.

With one leg the study volunteers did the conventional 80-percent-of-maximum lifts until they reached fatigue, at 8 to 10 reps. The other leg lifted 30 percent of maximum until fatigue set in, around 25 reps.

At the start of the study and 10 weeks later, the researchers put all the volunteers into MRI scanners to measure their quadriceps. There was essentially no difference between the heavy and light lifters. The results appear in the Journal of Applied Physiology.

To translate all this into concrete terms, Phillips says an inexperienced lifter might be able to manage a single knee-extension weight of 220 pounds. Eighty percent of that would be 176 pounds and 30 percent would be 66 pounds.

Exercising different muscles will involve different weights and different number of reps before fatigue sets in. For instance, most people will be able to do more reps of a biceps curl because the biceps doesn't tire as fast.

Phillips says one big advantage of lifting lighter weights is that it's easier on the joints — the limiting factor for many older people. "Lifting with lighter weights is one great way around that," says Phillips, 45, who has modified his own exercise regimen to incorporate lighter weights with more reps.

Next his group is going to repeat the experiment, first with middle-aged people and then with volunteers up to 85 years old. Earlier studies have shown that even nonagenarians can rebuild muscle mass with careful weight training.

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