Background: Firefighter helmets are essential protective gear but add significant weight (average 22 kg for full gear), potentially causing neck muscle fatigue and musculoskeletal disorders. While previous studies have focused on static loads or simple movements, few have analyzed the effect of helmet wear on muscle activity during dynamic, multi-planar movements at different pace. Objects: This study aims to evaluate the effects of wearing a standard Korean firefighter helmet on cervical muscle activity and kinematics during three dynamic head movements (flexion–extension, lateral flexion, and rotation) performed at two different pace. Methods: Twenty-four healthy adults participated in this study. Subjects performed three cervical movements at 45 and 75 rpm guided by a metronome, both with and without a helmet. Kinematics were measured using electromagnetic sensors, and electromyography was recorded from the sternocleidomastoid (SCM), upper trapezius, splenius capitis, and cervical erector spinae (CES). Data were analyzed using repeated measures ANOVA. Results: Helmet wear significantly increased SCM activation during the deceleration phase and CES activation during the acceleration phase (p < 0.05) of neck extension. Higher movement pace (75 bpm) significantly increased peak angular velocity and muscle activation across most tasks compared to the slower pace (45 bpm). However, the interaction between helmet wear and pace was not statistically significant. Conclusion: Wearing a firefighter helmet increases the demand on specific cervical muscles, particularly the SCM and CES, to control head momentum and stability. Movement pace appears to be a more dominant factor in increasing muscle load than helmet weight alone in healthy subjects. These findings contribute to the ergonomic design of future firefighter helmets.

INTRODUCTION
MATERIALS AND METHODS
RESULTS
    1. Flexion–Extension
    2. Rotation
    3. Lateral Flexion
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• Dami Yang(Department of Physical Therapy, College of Bio-Health)
• Jangwhon Yoon(Department of Physical Therapy, College of Bio-Health, Department of Physical Therapy and Basic Science Institute, Hoseo University, Asan, Korea) Corresponding author