Not sure your research question, but your task doesn't sound like a typical 'dual task'. http://www.ncbi.nlm.nih.gov/pubmed/24248857

Look at that paper- generally there is a constant task (e.g. standing on foam surface) and one variable task (e.g. color-naming task). Having piloted some of these theoretical tasks, there is a sharp increase in complexity. 

Shouldn't the EMG signal be similar during regular soccer tasks? After all the same task is still being accomplished, just with added cognitive demands.

Hi Mr. Wittbrodt

Thanks for your response!

Firstly, the objective of this research was to find the postural and muscular behavior through the analisis of the APAs and APCs (postural adjustments). So, I made some pilotes studies and there was a significant differences among the participants. Of course, when the group is formed by the athletes there is a tendency a standard of the movement (Principle of Control Movement). In this case, there was a standard for the kicking performance, they adopted a very close strategy to execute the tasks (single vs dual-task). However, we observed that a secondary task modified the parameter of muscle activation, and the postural adjustments. In this case, specifically, we analized the behavior of the postural muscles. For this experiment there were others parameters analyzed that confirmed our initial hypothesis!

The following papers maybe help you:

Boonstra, T. W., van Wijk, B. C. M., Praamstra, P., & Daffertshofer, A. (2009). Corticomuscular and bilateral EMG coherence reflect distinct aspects of neural synchronization. Neuroscience Letters, 463(1), 17–21. http://doi.org/10.1016/j.neulet.2009.07.043

Clark, D. J., Kautz, S. A., Bauer, A. R., Chen, Y. T., & Christou, E. A. (2013). Synchronous EMG activity in the piper frequency band reveals the corticospinal demand of walking tasks. Annals of Biomedical Engineering, 41(8), 1778–1786. http://doi.org/10.1007/s10439-013-0832-4

Collins, D. F., Knight, B., & Prochazka, a. (1999). Contact-evoked changes in EMG activity during human grasp. Journal of Neurophysiology, 81(5), 2215–2225.

Cools, A. M., Declercq, G. A., Cambier, D. C., Mahieu, N. N., & Witvrouw, E. E. (2007). Trapezius activity and intramuscular balance during isokinetic exercise in overhead athletes with impingement symptoms. Scandinavian Journal of Medicine and Science in Sports, 17(1), 25–33. http://doi.org/10.1111/j.1600-0838.2006.00570.x

Fisher, R. J., Galea, M. P., Brown, P., & Lemon, R. N. (2002). Digital nerve anaesthesia decreases EMG-EMG coherence in a human precision grip task. Experimental Brain Research, 145(2), 207–214. http://doi.org/10.1007/s00221-002-1113-x

Granata, K. P., Padua, D. A., & Abel, M. F. (2005). Repeatability of surface EMG during gait in children. Gait and Posture, 22(4), 346–350. http://doi.org/10.1016/j.gaitpost.2004.11.014

Guidetti, L., Rivellini, G., & Figura, F. (1996). EMG patterns during running: Intra- and inter-individual variability. Journal of Electromyography and Kinesiology, 6(1), 37–48. http://doi.org/10.1016/1050-6411(95)00015-1

Hanson, A. M., Padua, D. A., Blackburn, J. T., Prentice, W. E., & Hirth, C. J. (2008). Muscle activation during side-step cutting maneuvers in male and female soccer athletes. Journal of Athletic Training, 43(2), 133–143. http://doi.org/10.4085/1062-6050-43.2.133

Hashimoto, Y., Ushiba, J., Kimura, A., Liu, M., & Tomita, Y. (2010). Correlation between EEG-EMG coherence during isometric contraction and its imaginary execution. Acta Neurobiologiae Experimentalis, 70(1), 76–85. http://doi.org/10.1016/j.jneumeth.2008.07.019

Kim, M. H., Yi, C. H., Yoo, W. G., & Choi, B. R. (2011). EMG and kinematics analysis of the trunk and lower extremity during the sit-to-stand task while wearing shoes with different heel heights in healthy young women. Human Movement Science, 30(3), 596–605. http://doi.org/10.1016/j.humov.2010.09.003

Laursen, B., Jensen, B. R., & Sjøgaard, G. (1998). Effect of speed and precision demands on human shoulder muscle electromyography during a repetitive task. European Journal of Applied Physiology and Occupational Physiology, 78(6), 544–548. http://doi.org/10.1007/s004210050458

Lovell, G. A., Blanch, P. D., & Barnes, C. J. (2012). EMG of the hip adductor muscles in six clinical examination tests. Physical Therapy in Sport, 13(3), 134–140. http://doi.org/10.1016/j.ptsp.2011.08.004

Magnusson, S. P., Simonsen, E. B., Dyhre-Poulsen, P., Aagaard, P., Mohr, T., & Kjaer, M. (1996). Viscoelastic stress relaxation during static stretch in human skeletal muscle in the absence of EMG activity. Scandinavian Journal of Medicine & Science in Sports, 6(6), 323–328. Retrieved from http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=9046541

McClelland, V. M., Cvetkovic, Z., & Mills, K. R. (2012). Rectification of the EMG is an unnecessary and inappropriate step in the calculation of Corticomuscular coherence. Journal of Neuroscience Methods, 205(1), 190–201. http://doi.org/10.1016/j.jneumeth.2011.11.001

McCurdy, K., O’Kelley, E., Kutz, M., Langford, G., Ernest, J., & Torres, M. (2010). Comparison of lower extremity EMG between the 2-leg squat and modified single-leg squat in female athletes. Journal of Sport Rehabilitation, 19(1), 57–70.

Mileva, K. N., Morgan, J., & Bowtell, J. (2009). Differentiation of power and endurance athletes based on their muscle fatigability assessed by new spectral electromyographic indices. Journal of Sports Sciences, 27(6), 611–623. http://doi.org/10.1080/02640410802707011

Noyes, F. R., Barber-Westin, S. D., Fleckenstein, C., Walsh, C., & West, J. (2005). The drop-jump screening test: difference in lower limb control by gender and effect of neuromuscular training in female athletes. The American Journal of Sports Medicine, 33(2), 197–207. http://doi.org/10.1177/0363546504266484

O’Shea, S., Morris, M. E., & Iansek, R. (2002). O’Shea S 2002 Dual task interference during gait in people with Parkinson disease effects of motor versus cognitive secondary tasks. Physical Therapy, 82(9), 888–897. Retrieved from papers://5a68cd75-9e27-4626-8d94-057f1df96060/Paper/p594\npapers://5a68cd75-9e27-4626-8d94-057f1df96060/Paper/p405

Sinopoli, K., Chen, J.-K., Wells, G., Fait, P., Ptito, A., Taha, T., & Keightley, M. (2014). Imaging “brain strain” in youth athletes with mild traumatic brain injury during dual-task performance. Journal of Neurotrauma, 1859, 1843–1859. http://doi.org/10.1089/neu.2014.3326

Solnik, S., Rider, P., Steinweg, K., Devita, P., & Hortob??gyi, T. (2010). Teager-Kaiser energy operator signal conditioning improves EMG onset detection. European Journal of Applied Physiology, 110(3), 489–498. http://doi.org/10.1007/s00421-010-1521-8

Sylos-Labini, F., La Scaleia, V., d’Avella, A., Pisotta, I., Tamburella, F., Scivoletto, G., … Ivanenko, Y. P. (2014). EMG patterns during assisted walking in the exoskeleton. Frontiers in Human Neuroscience, 8(June), 423. http://doi.org/10.3389/fnhum.2014.00423

Tikkanen, O., Hu, M., Vilavuo, T., Tolvanen, P., Cheng, S., & Finni, T. (2012). Ventilatory threshold during incremental running can be estimated using EMG shorts. Physiological Measurement, 33(4), 603–614. http://doi.org/10.1088/0967-3334/33/4/603

Verhaeghen, P., Steitz, D. W., Sliwinski, M. J., & Cerella, J. (2003). Aging and dual-task performance: a meta-analysis. Psychology and Aging, 18(3), 443–460. http://doi.org/10.1037/0882-7974.18.3.443

Winter, D. A., & Yack, H. J. (1987). EMG profiles during normal human walking: stride-to-stride and inter-subject variability. Electroencephalography and Clinical Neurophysiology, 67(5), 402–411. http://doi.org/10.1016/0013-4694(87)90003-4