Sports Medicine Research: In the Lab & In the Field: Guest Post: Trunk Muscle Activity During Various Exercises (Sports Med Res)


Wednesday, June 8, 2011

Guest Post: Trunk Muscle Activity During Various Exercises

An electromyographical comparison of trunk muscle activity during isometric trunk and dynamic strengthening exercises.

Comfort P, Pearson SJ, Mather D. J Strength Cond Res. 2011 Jan;25(1):149-54.

With low back pain accounting for a significant portion of musculoskeletal discomfort and affecting a large percentage of the general population, it is important to identify exercises that help strengthen the lumbopelvic-hip complex, also referred to as the core region. Comfort et al, compared trunk muscle activity between isometric (prone bridge and superman) and dynamic (back squat, front squat, and military press) strengthening exercises. 10 healthy males (age 21.8 ± 2 years; weight 82. 7 ± 10.8 kg) with recreational experience in resistance training performed each exercise in a randomized order. The prone bridge was a traditional forward (sagittal) plane exercise and the superman exercise required an isometric hold of lumbar extension while supported on a physioball (the article provides figures; 30-second holds). All dynamic exercises were completed with a standardized load (40 kg) and for 1 set of 3 reps with a 3-second count for the descent and ascent phases of the exercises. Two surface electromyography (EMG) electrodes were placed on each the rectus abdominus and erector spinae muscles to record muscle activity; which was collected during the accent and decent phases of the exercises. Comfort et al found that the prone bridge demonstrated the greatest rectus abdominus activity compared to all other activities. The superman exercise and front squat demonstrated the greatest erector spinae activity (with no difference between the two exercises). The authors propose the prone bridge may be the most suitable exercise for strengthening the rectus abdominus. For the erector spinae muscles they advocate initially using the superman exercise and progressing over time to the front squat (with a low to moderate load). They note that the front squat may be beneficial because it can be progressed by increasing the loading and it may be more applicable to activities of daily living or sporting activities.

EMG analysis of core muscles has helped clinicians select exercises for strengthening the lumbopelvic-hip regions. Ekstrom in JOSPT (Dec. 2008) analyzed longissimus thoracis and lumbar multifidi muscle activity in 14 different exercises used in low back strengthening programs. Ekstrom’s data was helpful because it classified the exercises in terms of intensity (low to high). Escamilla (JOSPT, May 2010) and Imai (JOSPT, June 2010) both looked at core muscle activity with swiss ball and stable/unstable surfaces. All of theses studies help clinicians select the best possible exercises to strengthen the core region, based on the needs of the patient/athlete. What I found interesting in this study was the comparison of isometric and dynamic activities. As in any strengthening program, the ultimate goal is the restoration or improvement of function. This study looked at different functional tasks (squatting, overhead lifting) and provided useful data that clinicians can use during the rehab process. The importance of core strength is vital for lumbar and lower extremity function and research like this and the others studies help the clinician in developing programs from lower to higher intensity while focusing on certain muscle groups through individual exercises or dynamic activities. For example, Comfort et al recommended that we progress superman exercise to front squats. It would be interesting to hear input from other clinicians as to the importance or core strengthening and more specifically the thought process with the selection of exercises related to studies like these noted today. Being one that weighs EMG studies pretty strongly, especially with core, hip, and scapular regions, I often wonder where other clinicians fall with this type of research.

Written by: Tom Martin
Reviewed by: Jeffrey Driban

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Anonymous said...

I am a budding clinician and on the side personal trainer. I think that core stability is very important especially when performing dynamic weight lifting activities. I would agree with the author's suggestions and like these type of studies because they help me pick out exercises that can help with the baseline stability of someone I'm working with. However, when I coach someone who is weight lifting, I tell them to "engage their core" during any lift (squat and military press included) for balance and protection of injury that could come from improper posture if trying to push out too many repetitions. I am hoping that the trainee pulls their abs in toward their spine (similar to what is talked about during some yoga moves) which to me is providing good core stability during these lifts.

It seems like this study did not instruct the lifters to actively "engage their core" during the dynamic lifts, so I wonder if I am helping my trainees or providing something useless? Any thoughts?

Andy Kubinski, MS

Tom Nowakowski said...


Great post! Couldn't agree more that core strengthening is vital to improved function, whether from an injury or performance standpoint. I understand the thought but do not agree with the authors in the statement that they recommend progression of the superman exercise to the front squat without a clarifier. I organize these exercises differently in my head.

To me, the superman is a component exercise and the front squat is a compound exercise. If the front squat cannot be performed, it should be broken down into mobility drills while you use component exercises to build "segmental" strength to achieve your desire of a successful front squat. The concept always driven into my head is that strength training cements your mobility and posture.

Andy, I believe you are truly helping your trainees because everything we do in the weight room and in our ADLs includes contributions from the core. Many times improper form occurs even in the most well-intentioned individuals due to poor core strength/stability. The thought I can contribute to you is that when you encourage your clientele to "engage the core" do not focus only on drawing the abs toward the spine. Again, thats only one aspect of the core. I just recently read a great article that stated to optimally engage the core our patients must not only do what you mentioned but also "pull their knee caps up", squeeze their backsides and engage the lats to truly "engage the core". I have just started using those cues and works much better so I thought I'd share it with everyone!

Tom Martin said...


Thanks for the comments.
I think it is safe to say we all agree with the importance of core/trunk stabilization.
What always intrigued me was the progression of exercises and verbal cues.
Where I have let the evaluation/patient goals/and current research guide my exercise progression, the verbal cues differ when this topic arises with colleagues.
I start with instruction of the "abdomenal draw in manuever" to focus on Transverse Abdomenus (TrA). Others will perform an abdomenal bracing manuever in nuetral spine, which appears to focus on Rectus Adomenus (RA).
I value this initial phase bc in my opinion the TrA is the main stabilizer to the L/S based on research back in the day by Richardson and Panjabi (to the best of my recollection)
I will teach this and instruct patients to perform it t/o the day;when sitting/driving/walking/washing dishes etc.(even if it 1-2 times)
Progression t/o mat exercises to unsupported sitting to standing to functional positions, based mainly on tolerance.
I agree with both of you guys with the need of verbal cues t/o the process.

I would love to hear more regarding the thought process with exercises and verbal cues used early in the process.

Do clinicians utilize bracing or draw in techniques??
Does anyone really care which abdomenal ms is being isolated??

Donatella Nobatti said...

Nice post!!! Well core strength is all that it takes.

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