If you're reading this, you are probably no stranger to core strengthening. You might be trying to improve your running performance, get through the work day without back pain, or reclaim your body now that the baby is here. Maybe you're thinking that your gym routine needs some updates.
The last post I wrote discussed some reasons that a strong core is important for everyone, not just athletes and not just cover models. It also dissected the plank, delineating the benefits and the limitations. The ultimate conclusion was that the plank may be a good starting place for abdominal strengthening, but total core engagement requires some other tools as well.
My name is Dr. Allan Buccola, physical therapist and owner of Impetus Physical Therapy in Greensboro, NC. If core strength is important for all people, then finding the most efficient way to achieve it is the purpose of this post. I don't know many people with a surplus of free time, so when the time is finally found to perform self care (exercise), it has to be efficient. I don't have time to waste when I'm at the gym and you probably don't either.
CAN A SINGLE EXERCISE ENGAGE THE ENTIRE CORE?
If there was one perfect exercise that hit every muscle group, then all of that 'core' time at the gym could be trimmed down from 45 minutes to less than 10. A stronger trunk might not require that entire 30 minute Pilates DVD. It would probably be easier to stick to a program that required less time anyway, right?
A 2010 study by Escamilla et al reviewed some of the most popular core exercises in order to gain a better picture of how they engage the core. Data was calculated showing percentage of maximal activation for each muscle, whereas >50% is considered necessary for actual strengthening to occur. The study looked at 4 different functional parts of the abdominal muscles, as well as the spine erectors, the lats, and the central part of the quads.
The results were surprising, as only a handful of these exercises were suitable for true abdominal strengthening. None of these exercises were able to activate the spine erectors greater than 10% of maximal effort. The lats and the central quads (rectus femoris) were also limited in engagement. The highest levels of engagement were found at the internal and external oblique abdominal muscles. Those are responsible for both creating and resisting rotational forces at the trunk and/or pelvis.
Although the plank is not included in this data set, the "decline push-up" makes for a close proxy. Be that as it may, its ability to activate the core pales in comparison to the other exercises. Surprisingly, the standard crunch is able to engage the upper part of the six-pack fairly well, but is not nearly as effective at engaging other abdominal muscles, makings it a one-trick-pony.
At the top of the list are dynamic exercises on a physioball. The roll-out exercise, performed on a physioball, proved to effectively activate the upper and lower portions of the rectus abdominis (six pack). At 63% of maximal voluntary contraction, it peaked higher than in any other exercise analyzed in this study. This would make it an ideal exercise for targeted abdominal strengthening, but might also make it a bit too difficult for beginners.
The pike on a physioball created the highest levels of activation in the external obliques at 84% of maximal contraction. These muscles are responsible for explosive rotational strength of the trunk. These would be vital in everything from golf swings to martial arts punching, but also critical in everyday tasks. The internal obliques showed high activation as well, a muscle pair thought to be responsible for stabilization and posture, resisting trunk rotation.
Some of the exercises in this study are shown to be great ways to target the obliques. These are critical for rotational stability and strength in the core, something easily missed by a standard plank. Unfortunately, there are other key core muscles simply not engaged.
Can The Side Plank Fill in the Gaps?
There is a plank version that is performed in side-lying. The side plank is often thought of as a lateral hip strengthening exercise, as well as a way to better target the oblique abdominal muscles. How does this version of the plank compare to the traditional plank? Can it better engage the core as a whole?
A 2014 study by Youdas et al. set out to answer this question by comparing 4 different versions of this muscle. The two muscles in question are the external oblique and the gluteus medius. Asserting that an activation level of >50% of maximal effort is needed for strengthening, they recorded electromyography data during the side plank in hopes to answer this question.
Authors also published data on three other muscles, the rectus abdominis (six pack), the large spine extensors, and the deep spine stabilizers. These other muscles are traditionally targeted through other isolated strengthening exercises, but not often thought to be targeted during core strengthening. The fourth version ("d" above) produced the highest activation overall.
The split rotational side plank ("d") elicited solid levels of activation in the gluteus medius (hip), but more importantly demonstrated the highest levels of activation for the other muscles overall. For the gluteus medius and external oblique, this exercise offered activation from 63-71% on average. Other side plank versions were equally as engaging for the gluteus medius, but much less so for the external oblique. These muscles often fire together during functional activity, so choosing an exercise that engages both well is ideal.
For the three other muscles studied, option "d" (see above) is the most engaging overall. For the rectus abdominus and longissimus thoracis, activation is readily measured in the 30-40% range, but fails to meet the standard of the >50% level needed for strengthening. The deep lumbar spine stabilizers demonstrated much lower levels of activation which is unfortunate.
The side plank comes closer to full core engagement, but still falls short. This exercise appears to be an excellent option for strengthening the core muscles on the sides of the body. The front plank has shown to better target the front of the core than sit-ups or crunches alone. Unfortunately, these exercises still leave out a critical part of the core. They fail to target the stabilizers of the spine in a meaningful way.
DEEP SPINE STABILIZERS
The deep spine stabilizers are often forgotten about. They lie deep to the large and bulky outer layers. Rather than producing high levels of force to move the back, these tiny muscles that lie close to the spine are able to stabilize the spine using less compressive force. They are made up of mostly slow twitch muscle fibers, ideal for firing for long periods of time, and because of this are considered postural muscles.
With only the studies above, it remains unclear the best ways to strengthen the deep stabilizers of the spine, the lumbar multifidus, as well as others. These deep postural muscles are largely involuntary. Activation is sometimes possible, but likely not in isolation, and even if possible would not be desired. These muscles work best when they know to fire automatically.
Physical therapists have found novel ways to help patients activate these muscles when they are under-performing or weak. This is often a strategy in physical therapy when the larger, more superficial muscles in the core become over dominating. Finding meaningful ways to strengthen them has been unclear to some degree.
As it turns out, involving this deep core layer may be more simple than you might think. In 2013, Martuscello et al authored a systematic review of core muscle activity during a wide variety of exercises. This review analyzed electromyography data from 17 studies assessing 93 different exercises.
Their analysis and recommendations were based on the deepest components of the core- the lumbar multifidus and the transverse abdominis. For simplicity, they categorized exercises into 5 groups to allow for more meaningful comparison (see below.) For the sake of this post, the majority of the exercises discussed in part one, The Plank Disassembled, would fit into these first three categories. The last two categories are often not considered 'core' exercises necessarily.
The authors findings were that activation of the deep core muscles was largely the same across the first three types of core based exercises, on both stable and unstable surfaces. Regardless of the minor differences between exercises, they were generally somewhat limited in their ability to activate the deep core stabilizers. Authors also note that during the free weight exercises, categories 4 and 5, activation of the deep core was highest for both multifidus and transverse abdominis.
The authors went further to say that their data suggest:
The suggestion is straightforward: don't waste time working on core-specific exercises when free weight exercises are more engaging. I only partially agree with this, mostly because total core engagement means more than just the deep layers. There's still great value in those other exercises specific to engaging the front and sides of the core. They have their place in a well-rounded core conditioning program.
The conclusion from this study also highlights how free weights, rather than machine based strengthening, make a good first option. Take a person who is performing abdominal crunches, leg lifts, and machine-based chest press, and move them to performing push-ups. The result is greater levels of activation and time saved. Of course, it's not always that simple.
Best Results depend upon Personalization
The unfortunate reality of the above scenario, particularly from the PT perspective, is that when coordinating these exercises, not all functional parts will be performing at the same level. Many people are able to perform a plank, but have not the chest strength to move along to push-ups solely. One of these muscle groups will be ultimately left on the sidelines, while the other is worked beyond capacity.
Conversely, someone with over development of the pecs might benefit from moving away from sit-ups and toward push-ups for combined core/chest workout, but potentially will not gain much benefit from the chest portion. This is one reason why so many of these exercise variations exist. This is why blindly recommending an exercise is unwise. This is why listening to your body is key. This is when personal trainers can be very beneficial.
Occasionally, these exercises need to be broken down into components to bring more attention to the weaker links of the kinetic chain.
THE TAKE HOME MESSAGE: Start Simple
Simply put, "most normal folk" seeking general strengthening or fitness will be best served starting out with a simple, total-body exercise program. This should include planks or roll-outs, side planks, squats, and deadlifts. Take time to learn the correct form at low weight and slowly work your way up from there. Learning the correct form for these exercises is equally as important as doing them in the first place!
The higher the intensity becomes (as strengthening becomes more aggressive), the more relevant strength imbalances will become. If good form is lost and compensations emerge, it may make sense to break movements down into simpler, isolated components. Balance will need to be restored before additional high-level efforts can resume.
Individuals may be unable to perform these exercises due to weakness. Those with pre-existing injury may require some program individualization. This is where physical therapists excel, as they prescribe exercise for patients along a functional continuum from hours after surgery to returning to sport: from pediatric to geriatric. It might be more appropriate to start with other exercises, but that doesn't mean the aforementioned will never be appropriate.
Many other movement specialists from personal trainers to yoga teachers and so on, are also able to find ways to modify their programs to better suit clients. As you are working with these professionals, be sure they are fully aware of any relevant injuries or pain. They can cater your program so that it is centered around your capabilities and/or limitations.
Final Note: Listen to Your Body
None of the exercises discussed in these posts are horrible, and none should be considered a panacea. Just because a study reports a particular exercise as being the best way to activate a certain muscle, does not mean this will be the case for everyone. Human movement is incredibly complex and variable, but your body often lets you know which muscles you are targeting.
No two people will require the exact same exercise program, but understanding which one is right for you can largely be figured out by listening to your body. Fitness professionals and experts in human movement can help with the rest if needed. We all come to exercise and strengthening at different ages and from different walks of life so choose exercises that are challenging, but not so difficult that you cannot do them correctly.
If your exercise program is too easy, then you might be wasting your time. It might be time to up your game.
Until next time, don't stop moving!