Holding plank for ever-increasing periods of time has become a staple of many gym classes. Fitness experts claim that staying at the top of a push-up builds core, strengthens back muscles, tones the arms and teaches endurance.
But one sports scientist suggests that holding the position for any longer than 10 second intervals is pointless.
According to Stuart McGill, emeritus professor of spine biometrics at the University of Waterloo in Canada, fitness fanatics will see greater gains from doing shorter holds more frequently.
He advises three bouts of 10 seconds as the ideal regime, and claims that classes which recommend minutes of planking are not useful.
"There's no utility to this kind of activity other than claiming a record," he said.
"Basically holding repeated holds of 10 seconds is best for the average person. But for people looking for better back health they should be doing the Big 3 everyday.
"This was the programme for the front, sides and back of the core musculature we developed a number of years ago.
"My conclusions come from many studies that we have performed, not just a single one."
The 'Big 3' involves curl ups, side-plank and bird dog, a pose which involves starting on the hands and knees the reaching out the opposite arm and leg.
All increase endurance of the muscles around the spine. He recommends starting with five reps, holding each position for 10 seconds, then four, three, two and one.
Professor McGill spent 30 years as a professor of spine biomechanics at the University of Waterloo where his laboratory has become a renowned destination for Olympic and professional athletes from around the world who are struggling with back pain.
Professor McGill also warned that the spine is more vulnerable in the morning, so advised being careful if doing back exercises first thing.
"Your discs are hydrophilic, which means and they love water, they suck up fluids, so when you go to bed at night you're actually shorter than when you wake up in the morning. And it's harder to put your socks on in the morning, your spinal discs are much more inflated, they don't like to bend and actually it has three times the stress.
"When we stress real spines they fracture much more than later on in the day. We would really advise against anyone getting up in the morning and doing bending exercises, pulling their knees to their chest, doing sit-ups and those kinds of things.
"They would be much wiser just to wait an hour, go for a walk, and let gravity squeeze out some of the water."
Back pain is the world's leading cause of disability. Every year, a total of one million years of productive life is lost in the UK because of disability from low back pain.
But Prof McGill said there were still "silly exercises" such as the speed sit-up, which causes back pain.