Straight leg abdominal exercise are commonplace in fitness classes, gyms and boot camps. Exercises such as scissors, six inches, throw downs and hanging leg raises pose a big challenge and “burn” for clients. However, they also pose a risk for the lumbar spine given the relatively poor abdominal control and lever arm created by momentum and the iliopsoas muscle.
Biomechanically speaking, the force on the lumbar spine is high as the legs come back down due to reverse muscle action via the attachment of the iliopsoas on the lower lumbar spine. This rapid and/or forceful descent causes a sizable shear force on the spine. This is why you will see the back arch or clients put their hands beneath the spine on the floor to try to get back to a neutral spine position instead of the hyperextended one they are experiencing as the abs are often unable to control the force.
Combining this long lever arm and poor abdominal stabilization is a recipe for injury over time, not to mention poor movement patterns. The exercise progression in this column will discuss how to work the abdominal region in a safe, effective way focusing on anti-extension of the lumbar spine as well as proper stabilization.
Execution: Lie on your back. Place both arms perpendicular to the body with he hand pointing to the ceiling. Next, bring the legs to a 90/90 position with the feet off the floor and find a neutral spine position. Slowly straighten and lower the left leg toward the floor to the lowest point where you can still maintain a neutral lumbar spine. Pause and return to the starting position. Now, perform the same movement on the right leg. Perform 5-10 repetitions on each side and repeat 2-3 sets.
1.Increase the cadence or time under tension
2.Move the opposite arm overhead as the leg is lowering
3.Move both arms overhead as the leg is lowering
4.Hold a medicine ball overhead during the leg lowering and eventually move it overhead during the leg lowering
1.Place both arms on the floor with the palms down
2.If it is still too difficult to maintain neutral spine alignment, place both arms on the floor with the palms down allowing for some recruitment of the lats to assist in the exercise
Application: This exercise is a safer way to work on abdominal strength and stabilization while minimizing shear forces on the lumbar spine. Keep in mind clients with tighter hip flexors may be even more at risk for lumbar strain with higher volume and ballistic movements if their form is off. I would advocate a slower cadence and fewer reps which is counter to most group exercise settings that encourage a fast pace and higher volume approach. Anyone with a history of disc pathology or prior lumbar strain needs to be very cautious with any straight leg abdominal exercises.