Neck Muscle Synergy During Arm Raise Exercises in Individuals With Chronic Neck Pain of a Traumatic and Non-Traumatic Onset Curtis SA1, Kallenberg LAC2, Burridge JH1 1 University of Southampton, Southampton, UK 2 Roessingh Research and Development, Enschede, The Netherlands E-mail: S.A.Curtis@southampton.ac.uk

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

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

Method – Array electrodes

Data RUTRP LUTRP RSCM LSCM Channels 1-3 Channels 5-7 Channels 9-11 Channels 13-15 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 Global RMS (GRMS) MUAP RMS (MRMS) MUAP RATE (MR) µV µV Epoch Epoch Epoch Lower MRMS (p<0.042) and higher MR (p< 0.075) were seen in the TO group compared to the HC and NTO groups.

Results – left upper trapezius MUAP RATE (MR) Global RMS (GRMS) MUAP RMS (MRMS) µV µV Epoch Epoch Epoch 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.

Results – right sternocleidomastoid Global RMS (GRMS) MUAP RMS (MRMS) MUAP RATE (MR) µV µV µV µV Epoch Epoch Epoch Epoch Epoch 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.

Results – right sternocleidomastoid Global RMS (GRMS) MUAP RMS (MRMS) MUAP RATE (MR) µV µV µV µV Epoch Epoch Epoch Epoch Epoch Epoch 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.

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. 1. This could result from these muscles being employed in a more postural role due to fear avoidance, as a result of pain. 2. possibly due to the muscle being painful or an increased reliance upon the UTRPs in maintaining this position. 3. The small TO group size mean the results should be interpreted with caution.

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. 57-63. Hermens, H. J., & Freriks, B. 1999, European recommendations for surface electromyography. Results of the SENIAM project. Roessingh Research and Development b.v., ISBN: 90-75452-14-4. (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