“Ask a PT” will be a weekly feature on Fridays in our blog, where we answer questions we get from our clients or posters on this site or our Facebook page. So if you have a question about some sort of injury or problem you are having whether pain or fitness related drop us a line in the comments or Facebook message, or you can email us at email@example.com.
This weeks question is a commonly asked question; should I do crunches to strengthen my core?
Many people believe that “crunches,” sit-ups, or any variation of an exercise where you lie on your back and curl up by using your abs are the best way to strengthen your core, or get that “six pack” stomach. While crunches may help with the six pack, and get your heart rate up, they are not shown to be very effective in creating “core stability.”
Core stability relates to the muscles that surround the spine, scapula, and pelvis that function to maximize force generation and minimize impact on the joints of the body, particularly of the spine. People often think of the core muscles as the “six pack” muscles, but the core also includes trunk muscles such as the lumbar paraspinals, transversus abdominis, the obliques, and even the diaphragm, as well as muscles further from the trunk such as the deltoids (shoulder muscles) and the glutes (hip muscles). These muscles work together to allow the body to maintain a stable position around which the limbs can manuever for a given task or activity.
Traditional ab workouts (i.e. crunches, bicycle sit-ups) are considered “isolation” exercises that really only emphasize the work of a single muscle, the rectus abdominis (the “six pack muscle”).
A more effective way to work your core is to do “integrative” exercise. An integrative exercise is one that requires activation of the main core muscles, including the rectus abdominis, obliques, paraspinals, as well as the more distal core muscles such as the deltoids and glutes. An example of this kind of exercise is a plank with alternate hip extension (see below) that challenges the body to maintain a stable position during movement of the extremities.
Bird-dog and single leg bridge, previous “exercise of the week” features on this blog, are also examples of integrative exercise (see http://ascentpt.wordpress.com/2013/09/25/exercise-of-the-week-bird-dog/ and http://ascentpt.wordpress.com/2013/09/18/exercise-of-the-week-single-leg-bridge/).
A study published in 2013 in the Journal of Strength and Conditioning Research shows that there is significantly greater activation of not only the rectus abdominis, but also of the more distal core muscles, with integrative core stability exercise compared with isolation exercise. So not only do integrative exercises help more to develop the six pack muscles, they will give you the added benefit of strengthening the entire core.
Another reason that crunches may not be a great exercise for you is that this causes repetitive loading of the spine into flexion. Flexion is the curved position of the spine that occurs when bending forwards, and is often a position in which injuries occur.
Since this is a position that should be generally avoided, it makes more sense to strengthen the core with a straight spine. This trains the muscles to stabilize the spine when performing tasks such as lifting, and will help prevent injury in the long run. For safe lifting tips, see http://ascentpt.wordpress.com/2013/09/30/safe-lifting-4-tips-to-avoid-low-back-pain/.
In summary, crunches are not the ideal exercise to strengthen the core. While they may help you get that “six pack,” integrative exercises will do that more effectively, in addition to providing you with longer term stability and injury prevention.