Background: Neck pain is the fourth most common musculoskeletal disorder globally. Heavy helmets worn in professions like firefighting contribute to neck muscle tension and pain. However, research on muscle activity with firefighter helmets in various static postures is lacking. Objects: This study aims to analyze the changes in electromyography (EMG) signals of the left sternocleidomastoid (SCM), left upper trapezius (UT), right splenius capitis (SPC), and left cervical erector spinae (CES) during various static head movements (upright, extension, lateral flexion, rotation, running) with and without a standard firefighter helmet. Methods: Twenty-four healthy adults (12 males, 12 females) participated. Subjects performed five static tasks in a randomized order with and without a helmet. Surface EMG was used to measure muscle activity. A paired t-test was used to compare conditions. Results: In the extension posture, SCM and CES activity significantly increased with the helmet (SCM: 21.49% to 24.31%, CES: 9.97% to 12.18%, p < 0.05). In lateral flexion, SCM activity significantly increased (19.66% to 19.95%, p < 0.05). In rotation, CES activity significantly increased (12.20% to 14.55%, p < 0.05). No significant differences were found for UT and SPC in most postures, nor for any muscle during the static running task. Conclusion: Firefighter helmet weight significantly increases muscle activity in the SCM and CES during specific static postures (extension, lateral flexion, rotation). These findings provide a basis for ergonomic improvements in helmet design to reduce neck fatigue.

INTRODUCTION
MATERIALS AND METHODS
RESULTS
    1. Left Sternocleidomastoid
    2. Left Upper Trapezius
    3. Right Splenius Capitis
    4. Left Cervical Erector Spinae
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• Yebin Shin(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