Dr Lee Brown, senior lecturer in strength and conditioning at the University of East London, says people relying on sit-ups to flatten their stomach are making a mistake.
"It's embedded in the archaic practices of boxing coaches and therefore everyone seems to follow it. But they're far from the best exercise for training your core," he told the Guardian.
Why sit-ups can cause back problems
Sit-ups involve lifting the upper body from a lying position towards the knees. They strengthen the abdominal muscles, hip flexors and chest, but Dr Brown says the abdominals are used far less than people imagine.
Doing too many can also be harmful. "If you're doing too many sit-ups, it can cause problems with the lower back. Overworking the hip flexors can make them hypertonic [stiff and tight]. Your torso leans forward because you have overly toned and tight hip flexors, creating an imbalance and a dumping ground for shearing forces in your lower back."
What to do instead
Dr Brown recommends planks, side planks, farmer's carries, suitcase carries and bird dogs. Pilates and yoga can also help build core strength.
He described working with a sprinter who had a back injury and had done sit-ups for years. The sprinter could hold a plank for less than 30 seconds, but six weeks later he could hold one for seven minutes and his back pain had gone.
Study findings
A study published in the Journal of Clinical Medicine involving 117 people with and without back pain found that those with back pain could hold a plank for "significantly longer" than those without, suggesting they had better abdominal strength. The research was carried out by Daemen University in New York.
