RESEARCH REPORT POSTER DISPLAY

EFFECT OF RELATIVE AND ABSOLUTE FATIGUE PROTOCOLS IN THE ASSESSMENT OF NECK MUSCLES FATIGUE IN WOMEN WITH CHRONIC NECK PAIN. Laliberté M¹, Larochelle J¹, Dumas J², Bilodeau M³, Arsenault B¹; ¹University of Montreal and CRIR-Montreal Rehabilitation Institute, Montreal (Qc), Canada. ²McGill University, School of Physical and Occupational Therapy, Montreal (Qc), Canada. ³University of Ottawa, School of Rehabilitation Sciences, Ottawa (Ont), Canada

PURPOSE: To contrast the discriminating power of two fatigue protocols, one involving relative and the other absolute force, when studying neck muscle fatigue in women with non traumatic chronic neck pain compared to healthy women. RELEVANCE: When evaluating neck muscle fatigue a relative protocol is often used with subjects sustaining a proportion of their maximal voluntary contraction (MVC). However, the real MVC may not be produced because of pain/fear in individuals with chronic neck pain. Consequently, a an absolute protocol, imposing the same load to all subjects, for the fatigue test may be more appropriate. No study has compared such different protocols. PARTICIPANTS: Thirty women with chronic (≥ 1 year) neck pain (CW) aged 31.1±8.3 years and 25 healthy women (HW) aged 33.0±8.5 years participated in this study. For the CW, mean score on the Neck Disability Index was 9.57±3.97. METHODS: For each subject, the MVC was first recorded in isometric neck extension in a sitting position. They then performed two 10s fatigue tasks, one using a relative load, the other an absolute load. The relative task imposed a 75%MVC load in extension, while the absolute one imposed the same load (16.7Nm) to all subjects. This load was equivalent to the 75%MVC of a sample of healthy women (n=15) previously evaluated. EMG signals were recorded with pairs of surface electrodes placed bilaterally on the splenius. Torque was measured in reference to C7-T1. The fatigue index used was the slope (Hz/s) of a series of EMG median frequencies (250 ms windows) over time during the respective task. ANALYSIS: Three way ANOVAs with repeated measures were used to compare the fatigue index between the two groups, the two fatigue tasks and both 2 sides. A t-test compared the strength between the two groups (alpha = 0.05). RESULTS: The CW (15.91±6.85 Nm) presented significantly less strength (19.61%) than the HW (19.79±6.26 Nm) in extension. For the splenius, no differences were found in the fatigue indices between protocols, sides and groups (e.g. fatigue indices for the left splenius: CW=-0.21 ±0.81 Hz/s; HW= −0.27±0.64 Hz/s). CONCLUSIONS: Our hypothesis was that CW would present higher levels of fatigue than HW in the absolute protocol. However, the CW did not present increased fatigability. It should be noted that 5 subjects from the CW and one from the HW were not able to complete the absolute task. The present absolute protocol aimed to impose 75%MVC. However, the task really corresponded to 94%MVC in HW and to 129% in CW. It appears that the development of an absolute protocol that can be generalized to different subjects is rather complex and would require measurements on larger samples of subjects in order to obtain the proper level of targeted load. IMPLICATIONS: A relative protocol appears to be appropriate to use with non-traumatic chronic neck pain women when studying fatigue of neck muscles. KEYWORDS: Fatigue, neck muscles, EMG. FUNDING ACKNOWLEDGEMENTS: Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), Ordre Professionnel de la Physiothérapie du Québec (OPPQ). CONTACT: recherche_cou@hotmail.com

ETHICS COMMITTEE: Ethics Committee of Center of Interdisciplinary Research in Rehabilitation of Greater Montreal