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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