Loading of the cervical spine in german police helicopter pilots

Introduction: Helicopter pilots and their crew frequently experience pain in the cervical spine, neck, shoulders, and head, known as general neck pain. With a lifetime prevalence of 81% among pilots and 84% among crew members, its occurrence in this group is high compared to the general population [1]. Besides individual discomfort, neck pain can affect motor control [2], concentration [3], and postural stability [4], potentially risking flight safety. This study investigates cervical spine loading in various head positions without and with helmet, and night-vision goggles (NVG). Based on these findings, training programs with specific exercises were developed for prevention.

Methods: Head, cervical spine and trunk movements of 16 German police helicopter pilots (43 ± 9 yrs, 1.80 ± 0.1 m, 84 ± 6 kg) were captured with seven IR cameras (100 Hz, Bonita, Vicon, Oxford, UK) in a stationary helicopter at the Düsseldorf Airport (Germany). The following head movements were repeated five times per pilot without helmet, with helmet (1.76 kg) and with helmet and NVG (3.01 kg): 1) view forward, 2) view to the right, 3) view to the bottom right, 4) view to the left, 5) view to the bottom left, 6) view to the top left, 7) view to the back left. External moment arms were calculated using marker coordinates, and joint moments about the cervical spine (C7) and muscle forces were estimated from literature data. A two-step ANOVA for repeated measures was used for statistical analysis.

Results: Without a helmet, external moment arms increased significantly (p < 0.001) by up to 40% for views to the bottom right (0.15 ± 0.01 m), bottom left (0.15 ± 0.01 m), and back left (0.17 ± 0.02 m) compared to the forward view (0.12 ± 0.01 m). For the typical flight position (view to the bottom right), moments increased significantly (p < 0.001) by 40% to 60% when pilots wore a helmet (0.14 ± 0.01 Nm/kg) or a helmet with NVG (0.16 ± 0.01 Nm/kg), compared to the flight position without a helmet (0.10 ± 0.01 Nm/kg). Considering an internal moment arm of 0.05 m [5], muscle forces ranged from 220 N to 320 N.

Conclusion: Training programs aimed at preventing neck pain should consider the muscle forces occurring during flight. For example, resistance bands used in neck muscle training should be much less stiff compared to those used for other muscle groups like the trunk, arms, or legs. Bands with lower stiffness (around 30 N of force at up to 50% stretch) would be more appropriate for carefully improving strength and coordination of the sensitive cervical spine muscles.

References:
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