Why shouldn't you do sit-ups?
You want to strengthen your abs by doing sit-ups. Right? Well, maybe it's not a good idea to use this exercise after all. Read on to find out why!
Let's break down a sit-up exercise into two movements. First, you do a curl-up (crunch) while your pelvis is still on the ground and then you flex your lumbar spine by lifting your pelvis off the ground. During the first part, your primary abdominal muscles contract concentrically and flex your torso. In the second part, however, your dominant agonist muscles are your hip flexors including psoas, TFL, and Sartorius. The abdominal muscles only act as the stabilizers in this second part. During this part, there is a significant compression force on the lumbar spine, which can increase the risk of spinal injuries such as disk herniation or pulled connective tissues.
The second part of a sit-up exercise doesn't add a remarkable value to it if your goal is to work the abdominal muscles. You should also be concerned about the second part if you have some postural conditions.
For example, if you have hyperlordosis (excessive lumbar curvature), there is a need to strengthen the weak abs muscles (These muscles become overstretched). However, since you have tight hip flexors with this condition, you don't want to promote the concentric contraction of the iliopsoas muscles and so you should avoid the second part. On the other hand, if you have a flat back posture (minor lumbar curvature), you don't want to promote the flexion of the lumbar spine and so it's wiser to skip the second part.
By following the risk and benefit ratio rule, it's recommended to keep the pelvis on the floor when you flex your torso. This way, while curl-ups(crunches) has the same benefits of sit-ups as an exercise for your abs, it's considered a much safer one.
Hooman Jamshidi Founder @Dur1 Health Registered massage therapist, Certified personal trainer E: firstname.lastname@example.org C: 416.726.4652