And Twisting Sit-Ups Don’t Train Your Obliques, Either
There are hundreds of different muscle groups in the human body. It’s complicated to try to figure out the exact role each muscle has. But every muscle works on the same basic principle:
When a muscle contracts, it exerts a force that shortens the distance between its two ends.
One of the major muscles of the abdomen – the rectus abdominis – connects the front of your rib cage to the pelvis. When the rectus abdominis contracts, it pulls the ribcage down towards your pelvis and bends your torso forward.
To highlight the action of the rectus abdominis, place one hand on your lower ribs and the other on your lower pelvis. Then bend your trunk so your two hands move closer to each other. That’s what happens when the rectus abdominis contracts. In the medical universe they call it trunk flexion.
When you do crunches, sit-ups, or curl-ups, you’re training the rectus abdominis to do its job of flexing the trunk.
But I’ve seen the downside in many of my patients — with sit-ups, curl-ups, or crunches you’re actually compressing your spine and putting more pressure on your discs. That’s why most people should steer clear of these exercises.
Fortunately, there are other muscles of the abdomen that lie below the rectus abdominis – the external and internal obliques and the transversus abdominis.
These deeper-lying muscles have a different architecture and a different function. One end is attached to the side of your lower ribs. And the other end connects to a stiff sheet of connective tissues in the front of your abdomen.
When the oblique and transverse abdominals contract, they also pull their two ends towards each other. But that doesn’t cause your trunk to flex. Instead, contracting these deeper muscles sucks your abdominal wall back toward your spine.
To picture the action, place one hand on the front of the abdomen and the other on the sides of your lower ribs. Now suck in your stomach to move your two hands closer to each other. There’s little actual trunk movement. That illustrates the action of the oblique and transverse muscles.
When the deeper abdominals fire, they improve your posture, make movement more efficient, and protect your low back. That’s why they’re the most important muscles to train.
The plank pose is a simple and effective way to train these muscles.
To help you organize a simple, safe, and effective workout for your own low back, here’s a link where you can download a free copy of Dr. Lavine’s Top 5 Exercises for Your Low Back.