RESEARCH REPORT POSTER DISPLAY

EFFECT OF TESTING POSITION ON THE MEASUREMENT OF NECK MUSCLE FATIGUE WITH EMG FATIGUE INDICES AND THE BORG SCALE. Larochelle J¹, Laliberté M¹, Bilodeau M², Dumas J³, Arsenault B¹; ¹University of Montreal and CRIR-Montreal Rehabilitation Institute, Montreal (Qc), Canada. ²University of Ottawa, School of Rehabilitation Sciences, Ottawa (Ont), Canada. ³McGill University, School of Physical and Occupational Therapy, Montreal (Qc), Canada

PURPOSE: To determine if a subject’s position (sitting/lying) has an effect on the fatigability of neck muscles, evaluated with EMG fatigue indices and rated on the Borg scale. RELEVANCE: Two main testing positions, sitting or lying, have been used in the evaluation of neck muscle fatigue. Contradictory results can be found in the literature comparing fatigue between healthy adults and adults with chronic neck pain. However, it is not known if the testing position could be a confounding variable. A reason that could possibly explain the differences in the level of fatigue observed may be that different testing positions lead to different recruitment of muscles involved in neck flexion or extension. PARTICIPANTS: Twenty-five healthy women (31.1±8.3 years) participated in this study. METHODS: The maximal torque relative to C7-T1 was recorded for a given position (sitting and supine lying) and a given task (neck isometric flexion and extension). This value served as the 100% maximal voluntary contraction (MVC). For the fatigue tests, the subjects were required to maintain a 10 seconds isometric contraction for each position and each task at 75% of their respective MVCs. EMG recordings were obtained with surface electrodes placed bilaterally on both splenius capitis and sternocleidomastoid (SCM) muscles. The EMG index of fatigue was the slope of a series (250 ms windows) of EMG median frequencies over time (Hz/s) during the contraction. Subjects rated their level of fatigue after each trial on a Borg-10 scale. ANALYSIS: For both tasks, the EMG fatigue indices were analysed with a two-way ANOVA for repeated measures, contrasting the factors position and side (left/right). Maximal torques and Borg scores were analysed using paired-t tests. RESULTS: The mean (± SD) flexion MVC exerted in sitting was 17.1±6.5 Nm and in lying 15.5±3.6 Nm. In extension, MVCs were 19.8±6.3 Nm for sitting and 26.2±5.8 Nm for lying. The difference between sitting and lying was significant (p < 0.05) for the extension task only. With regards to the EMG fatigue index, there was no difference between positions in flexion for both SCM. In extension, greater fatigue was observed in the lying position for both splenius (left and right splenius in sitting = −0.27±0.64 Hz/s and −0.05±0.74 Hz/s, compared to −0.50±0.63 Hz/s and −0.63±0.77 Hz/s in lying). Similar results were obtained with the Borg scores, as the subjects perceived more fatigue in the lying position for the extension task (3.7±1.2 in lying and 3.1±1.2 in sitting). CONCLUSIONS: The present findings suggest that testing position influences the results of strength and fatigue evaluations of neck extensor muscles. This was shown through dynamometry, an EMG fatigue index and the subject’s self-assessed fatigue on the Borg scale. IMPLICATIONS: When studying the literature on neck muscle fatigue, position should be considered as a confounding variable between studies. KEYWORDS: Fatigue, Neck muscles, EMG. FUNDING ACKNOWLEDGEMENTS: Fonds de Recherche en Santé du Québec, Ordre Professionnel de la Physiothérapie du Québec. CONTACT: jean-louis.larochelle@umontreal.ca

ETHICS COMMITTEE: Comité d’éthique de la recherche des établissements du CRIR