Neck Muscle Synergy During Arm Raise Exercises in Individuals With Chronic Neck Pain of a Traumatic and Non-Traumatic Onset Curtis SA 1, Kallenberg LAC 2, Burridge JH 1 1 University of Southampton, Southampton, UK 2 Roessingh Research and Development, Enschede, The Netherlands

Aim of the study To determine whether muscle activity differed in individuals with chronic neck pain in the upper trapezius (UTRP) and sternocleidomastoid (SCM) muscles during a sustained arm raise task. Subjects: Traumatic onset (TO, n =4) Non-traumatic onset (NTO, n =13) Healthy controls (HC, n =18)

Method Projected line Relaxed hand position Subjects performed bilateral shoulder abduction and maintained the position until fatigue resulted in the arms dropping below 90 o.

Method Simultaneous recordings of the UTRPs and SCMs were obtained using 4 x 4 linear array electrodes After Hermens & Freriks (1999). After Falla et al. (2002).

Method – Array electrodes

Data RUTRP LUTRP RSCM LSCM Channels 1-3 Channels 5-7 Channels 9-11 Channels The UTRPs were directly recruited in the arm raise activity. The SCMs could be recruited to stabilise the arm raise position.

Signal processing Wavelet template MUAP identified on three consecutive channels Motor unit action potentials (MUAPs) were detected from the recorded signals using an algorithm based on the Continuous Wavelet Transform.

Parameters measured Global root-mean-square (GRMS) Motor unit action potential root-mean-square (MRMS) Motor unit action potential rate (MR), the number of MUAPs per second The above parameters were estimated and changes over time, as well as differences between the groups, were investigated.

Results – right upper trapezius Lower MRMS (p<0.042) and higher MR (p< 0.075) were seen in the TO group compared to the HC and NTO groups. µV Epoch Global RMS (GRMS)MUAP RMS (MRMS) MUAP RATE (MR)

Results – left upper trapezius A trend for lower MRMS (p<0.134) and higher MR values (p<0.011) were seen in the TO group compared to the HC and NTO groups. µV Epoch Global RMS (GRMS)MUAP RMS (MRMS) MUAP RATE (MR)

Results – right sternocleidomastoid The TO group showed lower values for GRMS (p<0.027), MRMS (p< 0.042) and a trend for lower MR values (p<0.184) as compared to the HC and NTO groups. µV Epoch µV Epoch Global RMS (GRMS) MUAP RMS (MRMS)MUAP RATE (MR) µV

Results – right sternocleidomastoid The TO group showed lower values for GRMS (p<0.027), MRMS (p< 0.042) and a trend for lower MR values (p<0.184) as compared to the HC and NTO groups. µV Epoch µV Epoch Global RMS (GRMS) MUAP RMS (MRMS) MUAP RATE (MR)

Conclusions The lower MRMS and higher MR values in the UTRPS (TO group) suggest a greater proportion of small, low-threshold MUs activated more frequently. Increasing SCM activity was seen in all groups, possibly to help stabilise the arm raise position when the muscles directly involved became fatigued. However, reduced GRMS, MRMS and MR values seen in the TO group in the right SCM suggest they did not employ this muscle as much as the HC and NTO groups.

References Falla, D., Dall'Alba, P., Rainoldi, A., Merletti, R., & Jull, G. 2002b, Location of innervation zones of sternocleidomastoid and scalene muscles - a basis for clinical and research electromyography applications., Clinical Neurophysiology, vol. 113, pp Hermens, H. J., & Freriks, B. 1999, European recommendations for surface electromyography. Results of the SENIAM project. Roessingh Research and Development b.v., ISBN: (CD-ROM).

Acknowledgements I would like to thank Gerald Kerkut Trust and the School of Health Sciences (University of Southampton) for their generous support of this project