Written by: Maria Cheng, AP Medical Writer

LONDON (AP) – As the old exercise adage goes, no pain, no gain. So how much pain do you have to endure to benefit from weight training? Fitness experts say it depends on what you’re trying to achieve.

For years, some trainers have instructed gym-goers that to achieve the best results, they should train “to failure,” that is, until they are physically unable to do one more rep or exercise. But some recent studies suggest that this extreme regimen may only benefit certain people when applied to weight training.

“If someone wants to increase muscle mass as much as possible, training to failure is something to consider,” said Michael Zourdos, chair of exercise science and health promotion at Florida Atlantic University, who co-authored 55 studies. Articles on the subject in the journal Sports Medicine.

Zourdos and colleagues found that lifting weights “to failure” can build larger muscles but is not necessary to increase strength. People who work hard but don’t push themselves to exhaustion are likely to improve their health and fitness, he said. “There’s a difference between training for health and training for elite performance benefits,” he said.