HJL & JWR,
I am writing to give a brief comment on whether crunches or sit-ups, are important or relevant to the back. The spine is a series of over 50 joints. Those joints are “capsular-synovial” joints. (just like your knee, hip, and shoulder, just smaller) To say that a crunch, or sit-up is good or bad is way too generic… to the point that it is irrelevant. It is popular, often repeated, but not correct as it relates to its benefit, or detriment to the spine. Most joint pain is intra-capsular (within the joint). It is often a result of poor joint health, and bad “wearing” of the cartilage surface. Generic crunches, or sit-ups won’t help, or harm the joint.
All joints have 3-options. Normal movement (or joint-play), hypomobility (something is hindering normal motion), or hypermobility (slip/sheer….think blister). If a joint has degeneration (usually due to joint hypermobility) the cartilage surface is worn down. Forcing the surface to “rub” more, by doing a crunch, or sit-up, may make it worse, but more than likely won’t do much at all. A hypermobile joint can benefit from strengthening of muscles, but the abdominal muscles are at best, half of the solution. There are small muscles that follow your spine joints, and look sort of like the branches of a Christmas Tree going up your back called the Multifidi. These little muscles “literally” cross the small spine (facet or zygapophyseal) joints. If strengthening is needed, these little muscles are what’s really important.
Acute spine injury can be muscle related, but if it is very sharp, and one-sided (left side or right side of the spine), it is frequently a meniscoid pinch, or “entrapment”. Both crunches and sit-ups will drive this acute injury crazy, and make you hurt for a long time.
If the pain is starting in your back, and going down your arm or leg, anything into significant flexion (crunch movement), or extension (back arching), will likely make the radiculopathy much worse.
So, there’s nothing wrong with a crunch, or sit-up, if performed in a pain-free range-of-motion. If you have an injury, and cause a “new” sharp pain with your exercise, and keep performing the exercise, then you will be worse.. If you want to stay core-strong, great. That is good for prevention. If you already have back pain (or shoulder, knee, ankle, finger), that is now “pathology”, or traumatized, damaged tissue. Fitness exercise doesn’t ever fix pathological tissue. – D.W. (Physical Therapist & Athletic Trainer for 25 years)