ELECTROMYOGRAPHIC ACTIVITY OF THE CORE MUSCULATURE DURING PLANKS PERFORMED WITH AND WITHOUT INSTABILITY DEVICES Ronald L. Snarr1 and Michael R. Esco2 1School of Nutrition and Health Promotion, Arizona State University, Phoenix, AZ 2 Human Performance Laboratory, Auburn University at Montgomery, Montgomery, AL Results, cont. Introduction Abstract Figure 1. (upper right) EMG activity (mV) of the Rectus Abdominis (RA) Figure 2. (lower left) EMG activity (mV) of the External Oblique(EO) Figure 3. (lower right) EMG activity (mV) of the Lumbo-Sacral Erector Spinae (LSES) Instability devices have gained popularity within the fitness community for their purported “core” activation benefits. The two most common modalities are physio-balls and suspension devices. However, limited data exists on the neuromuscular activation patterns during traditional planks performed upon these devices. Therefore, the purpose of this investigation was to compare the EMG activity of the RA, EO, and LSES during planks performed on a stable surface, with a PB, and with a SD. Recent fitness trends have been geared towards incorporating instability methods such as Physio-Balls (PB) and Suspension Devices (SD). The purported advantage of these modalities is the increased muscular demand due to decreased stabilization. Limited research is available to determine the neuromuscular recruitment patterns of selected core muscles while performing an abdominal plank with the use of instability devices. PURPOSE: The purpose of this investigation was to compare the electromyographical (EMG) activity of the rectus abdominis (RA), external oblique (EO), and lumbo-sacral erector spinae (LSES) during planks performed on a stable surface (REG), with a PB, and with a SD. METHODS: Apparently healthy men (n = 6, age = 23.92 ± 3.64 years) and women (n = 6, age = 22.57 ± 1.87 years) volunteered to participate in this study. All participants performed three variations of the traditional plank. For each, the feet were securely placed on the ground, while the forearms were either placed on a stable surface (i.e., REG), on a PB, or on an SD. Each exercise was performed isometrically for five seconds. For this study, the order of the exercises was randomized to prevent fatigue error during data collection. Mean peak (raw) and normalized (%MVC) EMG values were recorded for each muscle group during each five second isometric exercise. RESULTS: Results are shown in Table 1. For the RA, the SD elicited a significantly greater raw and %MVC muscular activity as compared to the REG and PB. The REG showed a significantly lower RA activation (raw and %MVC)(p < 0.05) compared to either of the instability devices. In terms of the EO, the SD showed a significantly greater (p < 0.05) raw EMG activation than either the PB or the REG. The REG showed significantly lower EO active (p < 0.05) compared to the PB and SD. The PB and SD showed no significant differences in LSES. However, planks performed on both devices yielded significantly higher LSES EMG values compared to REG (p < 0.05). CONCLUSION: This study found significantly greater EMG activity in the RA, EO, and LSES when planks were performed with a Physio-Ball or a Suspension Device compared to the traditional method. However, results also indicated that when planks are performed with the elbows on the suspension device the EMG activity of the RA (raw and %MVC) and EO (raw) was greater compared to when the elbows were placed on a physio-ball. PRACTICAL APPLICATIONS: Practitioners should take note that traditional planks are an important exercise to target the RA, EO, and LSES. Instability devices, such as a physio-ball or suspension device appears to offer advanced progressions of the plank and may be desirable for those wanting an increased challenge of the core musculature. † * Methods Recreationally trained men (n=6, mean age = 23.92 ± 3.64, height = 178.64 ± 9.23 cm, weight = 85.32 ± 6.92 kg) and women (n=6, mean age = 22.57 ± 1.87, height = 173.55 ± 3.76 cm, weight = 68.78 ± 5.56 kg) volunteered to participate in this study. Subjects performed two, 10-second isometric contractions of REG, PB, and SD, where the order of the exercises was randomized. Average peak EMG activity was recorded and analyzed for all three movements in the rectus abdominis, external oblique, and lumbo-sacral erector spinae group. † * * Conclusion This study found significantly greater EMG activity in the RA, EO, and LSES when planks were performed with a physio-ball or a suspension device compared to the traditional method. However, results also indicated that when planks are performed with the elbows on the suspension device the EMG activity of the RA (raw and %MVC) and EO (raw) was greater compared to when the elbows were placed on a physio-ball. Results RA: SD elicited a significantly greater raw and %MVC muscular activity as compared to the REG and PB. The REG showed a significantly lower RA activation (raw and %MVC) compared to either of the instability devices. EO: SD showed a significantly greater raw EMG activation compared to PB and REG. The REG showed significantly lower EO active compared to the PB and SD. LSES: No significant differences in LSES between PB and SD. However, planks performed on both devices yielded significantly higher values compared to REG. Practical Applications Practitioners should take note that traditional planks are an important exercise to target the RA, EO, and LSES. Instability devices, such as a physio-ball or suspension devices, appear to offer advanced progressions of the plank and may be desirable for those wanting an increased challenge of the core musculature. However, further research is warranted for cross comparisons of varying types of instability devices (e.g., BOSU, dyna-discs, etc.) to determine core muscular activation during traditional movements. Table 1. Comparison of the raw (mV) and normalized (%MVC) EMG of the selected musculature between the different exercises. RAW %MVC RA EO LSES REG 0.81 ± 0.90* 0.56 ± 0.35* 0.10 ± 0.04* 36.1 ± 28.1* 42.0 ± 21.6* 10.0 ± 4.10* PB 1.34 ± 1.21† 0.75 ± 0.39† 0.17 ± 0.09 65.0 ± 44.0† 59.1 ± 40.9 17.5 ± 9.56 SD 1.98 ± 1.89 1.01 ± 0.54 0.17 ± 0.08 91.2 ± 65.7 75.9 ± 34.3 21.3 ± 10.8 References Beach, T.A.C., Howarth, S.J., Callaghan, J.P. (2008). Muscular contribution to low-back loading and stiffness during standard and suspended push-ups. Hum Movement Sci. 27, 457-472. Marshall, P.W., Murphy, B.A. (2005). Core stability exercises on and off a Swiss ball. Arch Phys Med Rehabil. 86, 242-249. McGill, S.M., Cannon, J., Andersen, J.T. (2013). Analysis of pushing exercises: muscle activity and spine load while contrasting techniques on stable surfaces with a labile suspension strap training system. J Strength Cond Res. 28(1), 105-116. Snarr, R.L., Esco, M.R., Witte, E.V., Jenkins, C.T., Brannan, R.M. (2013). Electromyographic activity of rectus abdominis during a suspension push-up compared to traditional exercises. J Ex Phys online. 16(3), 1-8. REG = Traditional plank, EB = Swiss Ball Plank, ET = Suspension device plank, RA = Rectus Abdominis, EO = External Oblique, LSES = Lumbo-Sacral Erector Spinae *Significantly lower compared to SD and PB (p < 0.05) †Significantly lower compared to SD (p < 0.05)