As I see people strenuously doing crunches and sit-ups at the gym, alone and with trainers, here is the case made by Harvard Medical School’s Focus on Fitness e-newsletter: yoga planks are good for core fitness, sit-ups and crunches are not good for the back.
A decade ago, sit-ups and grunting crunches were the standard for tight abs and slim waistlines. But research has proven that they are not effective and may actually cause harm. The repeated sit-ups push the curved spine against the floor with pressure causing damage to the compressed discs in the small of the back. Dr. Stuart McGill’s (known for his expertise on the back) work suggests that in some people the crunches may cause herniated discs.
Sit-ups can tug on tight hip flexors that are engaged in the movement–hip flexors are muscles that run from the thighs to the lumbar vertebrae. This results in lower back pain and discomfort.
Abdominal muscles are just a small group of core muscles. So using just a small group means the rest of the muscles are not worked.
Planks do not wear and tear the vertebrae. They also engage many more muscles–on the front, sides, and back. So they strengthen the whole torso, not just the abs.
In BBC’s Future series article, The surprising downside of sit-ups, a 2011 Illinois study had one group do daily sit-ups for six weeks and the control group did none. The sit-ups made no difference to waist size or the abdominal fat!
The BBC article states: “Research published in 2005 on soldiers stationed at the US military’s Fort Bragg attributed 56% of all the injuries sustained during the two-yearly Army Physical Fitness Test to sit-ups.”
One study suggests that it is not the wear and tear on the discs but genetics that predispose some people to back injury more than others.
Readers may also want to look at a previous post on this blog from November 7, 2011: