This study investigates how helmet properties—mass and center of mass (COM)—influence neck muscle fatigue to support the biomechanical design of firefighter helmets. Thirty-six firefighters (18 males, 18 females) performed sustained neck flexion and extension tasks under three conditions: no-helmet, US, and European-style (EU) helmets. Electromyography (EMG) data from eight neck muscles were collected. Fatigue was assessed using increases in normalized mean absolute value (NMAV) and decreases in median frequency (MF) of EMG signals. Signals were segmented into four intervals (0%–25%, 26%–50%, 51%–75%, 76%–100%), and regression analyses and ANOVA were applied to evaluate NMAV and MF values. Results showed that the US helmet led to greater muscle activation and fatigue. These findings highlight the importance of optimizing COM location—not just weight—when designing helmets to reduce neck injury risks.
CampbellR.MolisJ. L. (2022). Firefighter injuries on the fireground (pp. 1–11). National Fire Protection Association.
2.
ChoiK.-H.ChoM.-U.ParkC.-W.KimS.-Y.KimM.-J.HongB.KongY.-K. (2020). A comparison study of posture and fatigue of neck according to monitor types (moving and fixed monitor) by using flexion relaxation phenomenon (FRP) and craniovertebral angle (CVA). International Journal of Environmental Research and Public Health, 17(17), 6345. https://doi.org/10.3390/ijerph17176345
3.
ChowdhuryS. K.NimbarteA. D. (2015). Comparison of Fourier and wavelet analysis for fatigue assessment during repetitive dynamic exertion. Journal of Electromyography and Kinesiology, 25(2), 205–213. https://doi.org/10.1016/j.jelekin.2014.09.008
4.
ChowdhuryS. K.NimbarteA. D.JaridiM.CreeseR. C. (2013). Discrete wavelet transform analysis of surface electromyography for the fatigue assessment of neck and shoulder muscles. Journal of Electromyography and Kinesiology, 23(5), 995–1003. https://doi.org/10.1016/j.jelekin.2013.02.002
5.
CollocaC. J.HinrichsR. N. (2005). The biomechanical and clinical significance of the lumbar erector spinae flexion-relaxation phenomenon: A review of literature. Journal of Manipulative and Physiological Therapeutics, 28(8), 623–631. https://doi.org/10.1016/j.jmpt.2005.08.005
6.
CordoP. J.BellC. C.HarnadS. R. (1997). Motor learning and synaptic plasticity in the cerebellum. Cambridge University Press.
7.
EnokaR. M.DuchateauJ. (2008). Muscle fatigue: What, why and how it influences muscle function. The Journal of Physiology, 586(1), 11–23. https://doi.org/10.1113/jphysiol.2007.139477
8.
GallagherS.BarbeM. F. (2022). Musculoskeletal disorders: The fatigue failure mechanism. John Wiley & Sons.
9.
Global Burden of Disease Study (GBD). (2019). Global Burden of Disease Study 2019 (GBD 2019) results. Institute for Health Metrics and Evaluation (IHME). Retrieved from http://ghdx.healthdata.org/gbd-results-tool
10.
Harms-RingdahlK.EkholmJ.SchüldtK.NémethG.ArboreliusU. P. (1986). Load moments and myoelectric activity when the cervical spine is held in full flexion and extension. Ergonomics, 29(12), 1539–1552. https://doi.org/10.1080/00140138608967270
11.
KimS.JeongW. (2020). Physiological and psychological neck load imposed by ballistic helmets during simulated military activities. Fashion and Textiles, 7(1), 27. https://doi.org/10.1186/s40691-020-00218-x
12.
LarssonB.SøgaardK.RosendalL. (2007). Work-related neck–shoulder pain: A review on magnitude, risk factors, biochemical characteristics, clinical picture and preventive interventions. Best Practice & Research Clinical Rheumatology, 21(3), 447–463. https://doi.org/10.1016/j.berh.2007.02.001
13.
LeeJ.-Y.ParkJ.ParkH.CocaA.KimJ.-H.TaylorN. A.SonS.-Y.TochiharaY. (2015). What do firefighters desire from the next generation of personal protective equipment? Outcomes from an international survey. Industrial Health, 53(5), 434–444. https://doi.org/10.2486/indhealth.2014-0168
MurrayM.LangeB.ChreitehS. S.OlsenH. B.NørnbergB. R.BoyleE.SøgaardK.SjøgaardG. (2016). Neck and shoulder muscle activity and posture among helicopter pilots and crew members during military helicopter flight. Journal of Electromyography and Kinesiology, 27, 10–17. https://doi.org/10.1016/j.jelekin.2015.12.003
16.
NorasiH.HallbeckM. S.MirkaG. A. (2023). Neck extensor fatigue: Comparing the effect of 45 degrees of neck flexion to the effect of 45 degrees of trunk flexion. Proceedings of the Human Factors and Ergonomics Society Annual Meeting, 67(1), 668–672. https://doi.org/10.1177/21650666231178853
17.
PanjabiM. M. (1992). The stabilizing system of the spine. Part I. Function, dysfunction, adaptation, and enhancement. Journal of Spinal Disorders, 5(4), 383–389. https://doi.org/10.1097/00002517-199212000-00001
18.
PaulonG. M.SudeeshS.WeiL. H.ChowdhuryS. K. (2024). Firefighter helmets and cervical intervertebral kinematics: An OpenSim-based biomechanical study. Journal of Biomechanics, 176, 112364. https://doi.org/10.1016/j.jbiomech.2023.112364
