That seems to be the question among sport performance professionals when it comes to whether or not traditional trunk flexion exercises are appropriate for athletes.
Trunk flexion is the contraction of the abdominal musculature that brings your pelvis and sternum closer together – for example, during a crunch. Many activities of daily living require trunk flexion as well, including getting up out of bed in the morning and bending to tie your shoes.
Dr. Stuart McGill, a spine biomechanics researcher and an expert in preventing and treating low back pain, leads the charge against these flexion based exercises which have been the staple of core training programs for years.
Dr. McGill argues that focusing on traditional trunk flexion exercises:
- Can lead to chronic lower back pain- through the compression of intervertebral disks
- Neglects the majority of core musculature- it’s about more than just the 6-pack!
- Are not specific to the demands of sport- most sports aren’t done from the ground
So are crunches (and other trunk flexion exercises) bad for you? Will they injure your back and leave you ill prepared for athletic competition? Is there something else you should be doing?
Let us first address the definition of “core” as I think that there is a great deal of confusion as to what the term actually means. The core is much more than just “abs” or a 6-pack. The core is a group of muscles which surround and act on the spine to produce both movement and stabilization in the trunk.
The “core” is made up of the muscles of the abdominal wall, pelvic floor, lower back, and glutes, as well as the back extensors, hip flexors, and diaphragm.
It may help you to think of the core musculature as a box. In this analogy the “abs” make up the front of the box, which is targeted by traditional flexion based core training. The back extensors represent the back of the box, while the oblique muscles are the sides. The top and bottom of the box are the diaphragm and pelvic floor muscles respectively.
With the help of these muscles the spine can perform four basic types of movement: flexion, extension, rotation, and lateral flexion.
In general there are two basic ways to train the core musculature:
- Movement through the full range of motion (ROM) – flexion, extension, rotation, lateral flexion
- Bracing/anti-movements – extension, rotation, lateral flexion
Dr. McGill emphasizes the importance of “bracing” the core rather than putting the spine through exaggerated ROM which may cause excessive stress and damage to intervertebral disks potentially leading to chronic overuse injuries in the back. During this bracing technique, all of the core musculature is engaged simultaneously, thereby stabilizing the spine and avoiding spinal movement.
Bracing trains all of the core musculature unlike flexion heavy programs which target primarily the rectus abdominis and neglect other core muscles. Dr. McGill states that many sports, especially contact sports, can benefit from bracing type core training programs which can help stabilize the spine prior to impact and may reduce the risk of traumatic back injury in athletes.
McGill also stresses the lack of specificity in traditional core training for athletes, saying that few sports involve such extreme ROM performed from a supine (on your back) position from the floor. While most sports aren’t performed from the ground, trunk flexion is an important part of many sports including diving, hurdling, and gymnastics as well as many sports with overhead movements such as serving, spiking, or throwing.
So do the risks of performing trunk flexion outweigh the performance benefits? Should you avoid traditional trunk flexion exercises like crunches at all costs?
No, of course not. The trunk is made to bend. It’s a natural movement. Most sports require some amount of trunk flexion, and an athlete should train to be able to perform those requirements. Just don’t overdo it – use moderation, as in all things.
I recommend using a mixture of exercises:
- Including full range of motion as well as bracing/anti-movement exercises
- Targeting all four movements (flexion, extension, rotation and lateral flexion)
Dedicate one day per week to performing each type of core exercise (flexion, extension, rotation, and lateral flexion) each on a different day. This works great during the offseason if you are performing a 4 day per week program, but during the pre- and in-seasons, you may need to need to compress core training into fewer days.
McGill, Stuart. “Core training: Evidence translating to better performance and injury prevention.” Strength & Conditioning Journal 32.3 (2010): 33-46. Print.