A topic that comes up frequently on the FSRI blog is “core training,” particularly as it relates to moderating the lower back/spinal stress that training in all fighting arts creates. I dialogue quite a bit with people from various fighting arts circles, and often someone will respond to a core-related topic with “I do x reps of sit-ups everyday.” Ostensibly this seems like a good way to train the core musculature, however it neglects many important elements of the core’s movement and stabilization systems at the favor of the most visible aspect, the rectus abdominis (the “6-pack” that people are unfortunately obsessed with). Due to their positioning in the spinal column and the muscular attachments of several muscles, notably the psoas, the lumbar vertebrae end up being exposed to kinematic demands and kinetic forces that are greater than one might think. Full sit-ups actually increase these forces, since hip flexion is required along with the desired rectus abdominis action, which places a combined compressive and shearing force on the lumbar vertebrae of the lower back:
Clinicians often recommend abdominal exercises as both a prophylactic and a treatment for low back pain…However, sit-up type exercises, even when performed with the knees in flexion, generate compressive loads on the lumbar spine well over 3000 N (ed: 675 lbs. force) . According to one clinical report, the use of sit-up type exercises appears to have actually contributed to low back pain development among a group of 29 exercisers. Partial crunches have been advocated as providing strong abdominal muscle challenge, with minimal spinal compression (Hall, 2007).
The action of a full sit-up creates several surprisingly high forces: compression on the anterior (front) facets, tension on the posterior (rear) facets and shear at the medial rotation point of the lumbar spine, particularly the lower vertebrae.
If the goal is to correct the stresses that training and conditioning place on our lower backs by strengthening the rest of the core, it should be clear that full sit-ups are not a good choice, and that the RA muscle is not the best target for “core training.” Don’t forget the image of the core as a tall tower with guy wires stabilizing it in all directions. The other core movers and stabilizers also need proper conditioning Although the RA is visible and easy to target, standard sit-ups and targeting it exclusively may actually increase the stress load to the lumbar spine, worsening existing muscular imbalances, performance deficits and increasing the risk of low back pain/chronic injuries.
The solution is to leave full sit ups out of your conditioning routines. Take a look at Bob’s Back Brief article for some suggestions and links to video demonstrations of many core exercises which can add balance and increased performance- as well as decreased stress on the lumbar spine- to your conditioning.
Feel free to contact one of us for consultation and more ideas.
Hall, S.J. (2007). Basic Biomechanics (5th ed.) (p.305). New York, NY: McGraw-Hill.