Is there a call for new research?
This is not going to be yet another repetition of the general consensus on flexion exercises within the strength and fitness industry. Many people have turned their backs on flexion exercises because they believe it will harm the discs in the lumbar spine.
"I am not disputing previous research I am only stating that I am not convinced by the conclusions."
The study (1) that has scared people off from performing flexion exercises like abdominal crunches was performed on pig-spines wrapped in plastic without any support from a sufficient intra-abdominal pressure. Repetitive full range flexion was causing the disc damage and the conclusion was made that we have only got a certain number of full flexion cycles in our spine before it breaks.
Hodges (4)performed a phrenic nerve stimulation study of the diaphragm which showed that the resulting increased intra-abdominal pressure caused an extension motion in the lumbar spine.
Cholewicki and McGill (2) performed a fluoroscope study of power-lifters which showed them able to maintain their lumbar segments 2-3 degrees from full flexion even when performing heavy lifting. The ability to keep the spine out of danger was credited to their motor-control. I am sure motor control had a lot to do with it, but I would like to give some credit to their ability to create sufficient intra-abdominal pressure and thereby protecting the spine.
It has been documented that power-lifters and weight lifters (5) have hyper-trophy of their diaphragms and can generate a much greater transdiaphragmatic pressure. Even exercises like biceps curls and sit-ups have been shown to strengthen the diaphragm (3).
This is a call for some new research.
What difference would the proper activation of the core from the inside out via a synchronized diaphragm contraction have on the flexion range when exercising?
I would like to see a new study “crash-testing” the loading of the spine in flexion exercises but this time have the air-bags fitted (intra-abdominal pressure) which would prevent full flexion to occur.
I am not recommending people to start performing flexion exercises again; all I am saying is that I am not convinced they are as harmful as currently thought.
Am I doing some flexion exercises myself? Yes I am because I know I can generate a very strong IAP after working with DNS stabilization principles for the last 10 years. The secret is to avoid full flexion by developing a strong core from the inside out.
- Callaghan J P and McGill S M. Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clin Biomech 2001 16 (1) :28-37
- CholewickiJ, and McGill S M. Lumbar posterior ligament involvement during extremely heavy lifts estimated from fluoroscopic measurements. J Biomech 1992 25 (1): 17
- DePalo V.A., Parker A.L., Al-Bilbeisi F., McCool D. Respiratory muscle strength training with nonrespiratory maneuvers. Journal of Applied Physiology 96, 731-734, 2004
- Hodges PW, Cresswell AG, Daggfeldt K, Thorstenson A. In vivo measurement of the effect of intra-abdominal pressure on the human spine. J Biomech 2001;34(3): 347-53
- McCool FD, Conomos P, Benditt JO, Cohn D, Sherman CB and HoppinJr FG. Maximal inspiratory pressures and dimensions of the diaphragm. Am J. Respir. Crit. Care Med. 155, 1329-1334, 1997