What epic gym session is complete without strapping your ankles to the decline bench and violently slamming your back against the pads until either your spine loses the ability to move or your hip flexors end up in a full-blown spasm?
The decline sit-up has its merits for experienced lifters when executed properly, but as soon as ego and added weight get thrown into the equation, this old-school staple can quickly get ugly, leaving you in a world of pain.
The Problem: Shear Force and Destabilization
To the average person, the decline sit-up seems similar to the traditional horizontal sit-up: same muscle group, similar motion. But after breaking down the intricacies of both movements, they can be deceivingly dissimilar and potentially harmful when not treated as two separate exercises.
Where things get a little more complicated is when you look at the force and range of motion produced by the decline sit-up by increasing the decline-angle of the bench when compared to the flat sit-up. Due to the downward angle, the moment arm of the motion becomes notably longer, which increases the potentially debilitating shear forces through the mid to lower segments of the lumbar spine.
The angle of the bench also creates more available range of motion for the spine to move through while sitting up. More range of motion means more time spent in extreme ranges, especially excessive thoracic and lumbar flexion. Forcing your spine repeatedly into end range flexion can potentially cause some structural and soft tissue damage to the posterior and lateral structures of the spine and trunk.
The decline sit-up can be risky enough when using perfect mechanics, but the risks get out of hand when people mindlessly manipulate the following variables:
- Increasing the speed of the movement
- Increasing the load (holding a weight plate)
- Twisting, bending, or turning during end range spinal flexion
If you're going to continue to use the decline sit-up in your program, perfect your movement using controlled muscular contractions and maintain as close to neutral posture as possible. If you don't, you'll end up paying the price.
A Better Exercise: Vertical Plate Press
This exercise can target the abs to produce some serious results through the core.
- Position the hips and knees at a 90-degree flexed position to eliminate involvement from the superficial hip flexors.
- Hold a weight plate directly in front of your chest with arms extended and press vertically under control.
The rectus abdominis muscle is a prime spinal flexor that runs from the bottom of the sternum to the pubic bone. Due to these anatomical landmarks, this muscle can still be highly active even when the spine stays in a relatively neutral position during the 90-degree vertical plate press.
The other key advantage to this movement is that it can be periodized and programmed for progressive overload. Over time, you'll be able to stabilize and move more weight as your strength increases.