A new study was recently published in JOSPT by my friend Rafael Escamilla to assess core muscle activation during Swiss ball and traditional abdominal exercises. This is a great research topic as the Swiss ball (or physioball, exercise ball, etc.) is widely believed to enhance core EMG. Selecting core exercises is typically more complicated than most people think. Sometimes I worry that too many people just try to create new exercises that look different and promote them as new “functional” techniques without any efficacy or research validation. Articles like this help us select the most appropriate exercises as much as we can.
Abdominal Exercises
Exercises on the physioball included the pike, knee-up, skier, decline push-up, hip extension, roll-out, and sitting march. These were compared to the traditional crunch and sit up floor exercises.
Core Muscles Examined
The muscles evaluated were the upper rectus abdominis, lower rectus abdominis, external oblique, internal oblique, lumbar paraspinals, latissimus dorsi, and rectus femoris.
Results
The pike and roll-out were the most effective exercises in recruiting core musculature. These exercises are pretty advanced and should be considered the most aggressive. These may be more appropriate for the advanced patient or client.- The pike, roll-out, knee-up, and skier exercises all showed relatively high EMG activity compared to the crunch and sit-up exercises. These exercises also had high EMG activity of the latissimus and internal oblique, suggesting that these exercise may be good exercises to enhance core stability by tensioning the thoracolumbar fascia.
The decline push-up and hip extension exercises produced similar amounts of rectus abdominis, external oblique, and internal oblique activity compared to the traditional crunch and sit-up. This is interesting considering that these are upper and lower extremity exercises rather than what would be considered “core” exercises. The use of a physioball increases the contribution from the core. While this may be great for core training, I would hesitate to say that performing these exercises should replace traditional extremity exercises. 
While core activity may be enhanced, extremity activity is decreased. Something to consider when your goal is to enhance extremity activation. I see a lot of trends towards using unstable surfaces, which is fine, but needs to be used correctly in combination with traditional exercises.- No statistically significant difference in rectus adbominis activity was observed between the two traditional crunch and sit up exercises, however rectus femoris was significantly higher during sit ups. While this info is not new, it does continue to demonstrate that crunches should definitely replace sit ups in any training or rehabilitation program, especially when considering the greater intradiscal pressure and lumbar compression observed with the sit up.
- The discussion in this article is worth reading, the authors do a great job discussing core stability itself and the contributions of various core musculature. Of note, the authors highlight the potentially disadvantageous stress at the lumbar spine during hip flexion activities. This needs to be taken into consideration when designing core programs. People with lumbar disk pathology may want to at least initially avoid exercises that involve hip flexion, such as the sit up, skier, knee-up, and pike. More appropriate exercises may be the roll-out, decline push up, and crunch.
The pike and roll-out were the most effective exercises in recruiting core musculature. These exercises are pretty advanced and should be considered the most aggressive. These may be more appropriate for the advanced patient or client.
The decline push-up and hip extension exercises produced similar amounts of rectus abdominis, external oblique, and internal oblique activity compared to the traditional crunch and sit-up. This is interesting considering that these are upper and lower extremity exercises rather than what would be considered “core” exercises. The use of a physioball increases the contribution from the core. While this may be great for core training, I would hesitate to say that performing these exercises should replace traditional extremity exercises. 
Clinical Implications
As you can see, choosing core exercises is not a simple task. There are several factors that need to be assess in each individual. This article examined EMG activity, but the authors do a good job relating the info to core function in the discussion. The way I see it, we need to take 5 factors into consideration when designing core programs:
Pathology/function of the person – Injured and healthy people have two different challenges and goals for core stability. The same program will not work for both.- EMG activity of core musculature,
- EMG activity of surround musculature – especially the rectus femoris and psoas,
- Position of the lumber spine during exercises, and
- Function of the core musculature during movement – i.e. does the exercise produce an isometric stabilizing force or does it use concentric/eccentric forces to control core movement.
How does this article change the way you work with your patients and clients? I know I don’t routinely use some of these but will definitely reconsider for the right person. For those interested, I use the TheraBand exercise ball pictured above for my physioball exercises, click here for more information.
Escamilla, R. (2010). Core Muscle Activation During Swiss Ball and Traditional Abdominal Exercises Journal of Orthopaedic and Sports Physical Therapy DOI: 10.2519/jospt.2010.3073
