Is it possible to isolate my upper or lower abs with different ab exercises?
I hear this debate all of the time. Many say that it’s not possible to contract one part of the rectus abdominis over another, while others claim that you can.
Part of this is semantics…you can’t “isolate” one part or another. In other words, you cannot contract one portion while keeping the other completely dormant. However, I believe that you can “target” one part, or steer more activation toward one portion or another. When you look at the nerve supply for the abdominal muscles you will find that they are innervated by multiple nerves (i.e. the ventral rami of T7-T11, T12 (subcostal nerve), and L1 (iliohypogastric, ilioinguinal). This is nothing new; you can also target portions of the the gluteus maximus, deltoids, pecs, etc.
I’m not particularly passionate about this topic because 1) Getting 6-pack abs is 90% about reaching low bodyfat levels and 10% about having muscular abs, and 2) The differences in activation between upper and lower rectus abdominis (RA) activity aren’t so drastic that they’ll lead to huge differences in functional strength adaptations.
Around a year ago I was a bit curious about this topic so I conducted a bunch of comprehensive EMG analyses on the abdominals. While one of my core studies can be found on a TNation article here, I didn’t measure upper vs. lower RA activity in that experiment. I conducted two experiments where I measured upper vs. lower abdominal activity, the tables for which can be found in my glute eBook. I performed tons of the best and most challenging abdominal exercises, and I found that you can indeed target the upper or lower abdominals. “Shoulder to hips” flexion, or abdominal exercises that have you bringing your shoulders toward your hips such as crunches, activate higher levels of upper RA than lower RA. “Hips to shoulder” flexion, or abdominal exercises that have you bringing your hips toward your shoulders such as reverse crunches, activate higher levels of lower RA than upper RA. In regards to my EMG experiments and other EMG experiments, the hip flexors are too far away to interfere with the readings of the lower abdominals – the amplitude is proportional to the inverse square of the distance from the source. So I don’t believe that that is an issue. And my EMG data was normalized, so that’s not an issue either.
If we go by “the feel test,” I’ve performed various abdominal/core exercises for many years and I believe that I can feel my lower abdominals working harder when I do exercises like reverse crunches in comparison to exercises like crunches. And as I’m sitting here typing, I believe that I can segmentally contract the different portions of the abdominals to different degrees. I find it easy to alternate between flexing the lower abs pretty hard while keeping the upper abs slightly more relaxed, and tensing the upper abs pretty hard while keeping the lower abs slightly more relaxed – but I’m not sure how much this has to do with turning on other core muscles such as the transverse abdominis or diaphragm to create this effect. Maybe if I study Shakira hard enough the answer will come to me….
In addition, I’m taking a Graduate level Biomechanics course right now, I’ve read the literature on the topic, I’ve discussed the matter with professors and Biomechanists, and I’ve studied the anatomy. So I believe that I’m pretty qualified to address this matter.
Here are six different studies that indicate that you can preferentially activate one portion over the other:
There are some studies in the literature that fail to demonstrate the same pattern and therefore contain different conclusions, but most studies do show differences in upper and lower RA activity. I know that Dr. Stuart McGill feels otherwise and believes that these readings are incorrect due to issues with normalization, but I know some professors who are adamant that he’s incorrect on the matter. Furthermore, if you read McGill’s full paper on the topic you’ll see that hips to shoulder spinal flexion still gets you slightly higher lower than upper RA activity, and when you do shoulder to hip spinal flexion you get slightly higher upper than lower RA activity – it’s just not significant in his study – though I’d argue that he may have seen different results had he tested other exercises.
I don’t believe that this is that big of a deal in terms of selecting the best exercises – in addition to EMG, I look at other things like joint safety, specificity, tension in stretch position, ability to produce a pump, ability to produce hypertrophy, ability to transfer to another lift, ability to transfer to an athletic endeavor, joint ROM, ability to increase joint mobility or stability, how the exercise “feels,” etc. When choosing core exercises, I like to stabilize in all directional vectors, and I like to perform exercises that strengthen the hip flexors from time to time – a muscle group that should be strengthened in advanced athletes.