Measuring Neuromuscular Fatigue in Cervical Spinal Musculature of Military Helicopter Aircrew

Authors: Harrison, Michael F.1; Patrick Neary, J.1; Albert, Wayne J.2; Kuruganti, Usha2; Croll, James C.2; Carol Chancey, V.3; Bumgardner, Bradley A.3

Source: Military Medicine, Volume 174, Number 11, November 2009 , pp. 1183-1189(7)

Publisher: AMSUS - Association of Military Surgeons of the U.S.

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Abstract:

ABSTRACT

Neck pain and muscle function in aircrew have received considerable attention. We hypothesized normalized electromyography (EMG) frequency would provide insight into appropriate methods to assess muscle fatigue in helicopter aircrew. Methods: 40 helicopter aircrew performed isometric testing that included maximal voluntary contractions (MVC) and 70% MVC endurance protocols of extension, flexion, and left and right lateral flexion for cervical muscles. Bilateral muscle activity in the splenius capitis, sternocleidomastoid, and upper trapezius was monitored with EMG. Normalized mean EMG frequency was calculated for each muscle at the start and end of the 70% MVC trials to determine which muscles fatigued and limited force maintenance during each isometric movement. Results: For extension, the left and right splenius capitis fatigued by ~21-22% ( p < 0.01); for flexion, the left and right sternocleidomastoid fatigued by ~11-14% ( p < 0.01); for right flexion, the right sternocleidomastoid fatigued by ~15% ( p < 0.01); for left flexion, the left spenus capitis and left sternocleidomastoid fatigued by ~7.2% (p = 0.02) and ~11.2% ( p = 0.03), respectively; in no trials did the trapezius muscles display fatigue as measured by EMG. Conclusion: The smaller agonist muscles were the most susceptible to fatigue during submaximal isometric endurance movements in the cervical muscles of helicopter aircrew.

Document Type: Research article

Affiliations: 1: Faculty of Kinesiology and Health Studies, 3737 Wascana Pkwy, University of Regina, Regina, SK Canada S4S 0A2. 2: Faculty of Kinesiology, Lady Beaverbrook Gym, 2 Peter Kelly Drive, University of New Brunswick, Fredericton, NB Canada E3B 5A3. 3: United States Army Aeromedical Research Laboratory, Building 6901, Fort Rucker, AL 36362-0577.

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