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NVG: Why the Neck Pains?

An informal query on a professional forum whether helicopter pilots suffer from neck pain while using NVG (1), a small group chose to share their thoughts and concerns. Eight of the respondents affirmed that they had discomfort or pain, including disc prolapse and pressure on the nerves as reported by one pilot each. However, there were 5, with NVG flying hours varying between 400 to 1200, without any symptoms. In fact, one of the respondents suggested that a regular work out, to stay fit, helps prevent such pains and aches while using NVG. Interestingly, it was found that some NVG-helmets systems are better than others, and are even known to alleviate the pain that occurred with another NVG.

A review article by Parush et al.[2] discusses the human factors aspects of the physical effects of NVG mounted on helmets. They highlighted the following issues which determine the ease and comfort of use as well as the likely potential for strain or injury to the neck:-

  • Fit of helmet-NVG on varying head size and shape.
  • “Implications of gross and sudden movements” particularly during ingress and egress
  • Compatibility with immediate environment and also with other head-worn equipment, e.g. eye protection.

The incidence of pain in neck is widely reported by NVG users, including concerns for personal well-being and safety raised [3, 4, 5, 6].  It is reported that an increase in the load on the head, as in case of helmet-NVG, results in strain and fatigue of the neck, with potential for severe neck injury in case of crash/force landing. Various researchers have explored the likely reasons of “NVG-associated neck strain” [2]. This includes the following:-

  • NVG affects the trapezius muscle to cause muscular pain, as evident by lower levels of cytochrome oxidase [7, 8].
  • Helmet weight and resulting centre of gravity did not directly correlate with the neck fatigue [9].
  • It is likely that it is not the increased weight of the NVG but its loading in the frontal position that results in neck strain [10, 11].
  • There is an increase in electromyographic (EMG) activity of neck muscles [10, 11, 12] as well as increase in muscular strain of the muscles of the neck [13] due to frontal loading, as occurs with NVG mounted on helmet.

Anecdotally, aircrew have also reported headaches lasting less than an hour, after undertaking missions using NVG. The site was either forehead or between the temples. Such headaches were associated with visual strain and muscular symptoms [6]. This could be due to muscular strain as well as likely poor vision due to incorrect adjustment and focusing of NVG. Incidentally those susceptible may suffer episodes of migraine due to NVG scintillation [14]

Parush et al have surmised that the important consideration to reduce neck strain and fatigue is the aptly designed helmet mount to provide correct fit and comfort [2]. Personal standards of fitness, as aptly stated by hueyracer, with 700 hours of NVG, on PPRuNe, sums it all up, “The secret seems to be “staying fit”-working out, train (and stretch!) your muscles….” [1].

Reference

1. Discussion on PPRuNe Rotorheads Forum: NVG and Pain Neck

2. Parush A, Gauthier MS, Arseneau L, Tang D. The Human Factors of Night Vision Goggles: Perceptual, Cognitive, and Physical factors. Reviews of Human Factors and Ergonomics 2011; 7: 238-279

3. Shender, BS, Ostrander G, White D. Self-reported neck pain incidence in US Navy aircrew from 2004-2008 [Abstract]. Avi Space Environ Med, 2009; 80, 291.

4. Oppermann B, Hampson, G, Pascoe, GD. Neck injury incidence within the Royal Australian Air Force: An update, and a proposed way forward [Abstract]. Avi Space Environ Med, 2008; 79, 517.

5. Adam J. Results of NVG-induced neck strain questionnaire study in CH-146 Griffon aircrew (Tech. Rep. No. 2004-153). Toronto, Canada: Defence R&D Canada 2004.

6. Manton AG. Night vision goggles, human factor aspects: A questionnaire survey of helicopter aircrew. Journal of the Royal Army Medical Corps, 2000;146, 22–27.

7. Harrison MF, Neary JP, Albert WJ, McKenzie NP, Veillette DW, Croll JC. Cytochrome oxidase changes in trapezius muscles with night vision goggle usage. International Journal of Industrial Ergonomics, 2010; 40, 140–145.

8. Harrison MF, Neary JP, Albert WJ, Veillette DW, McKenzie NP, Croll JC. Helicopter cockpit seat side and trapezius muscle metabolism with night vision goggles. Avi Space Environ Med, 2007; 78, 995–998.

9. Barnaba JM, Wilson CW, Baez-Vazquez M. Safety qualification and operational assessment of a night vision cueing and display system. In PL Marasco, RW Brown, SA Jennings, & TH Harding (Eds.), Proceedings of SPIE–The International Society for Optical Engineering: Vol. 6955. Helmet- and head-mounted displays XIII: Technologies and applications. Bellingham, WA: SPIE Press. 2008.

10. Thuresson M, Äng B, Linder J, Harms-Ringdahl K. Neck muscle activity in helicopter pilots: Effects of position and helmet-mounted equipment. Avi Space Environ Med, 2003; 74, 527–532.

11. Thuresson M, Äng B, Linder J, Harms-Ringdahl K. Mechanical load and EMG activity in the neck induced by different head-worn equipment and neck postures. International Journal of Industrial Ergonomics, 2005; 35, 13–18.

12. Lecompte J, Maisetti O, Portero P, Guillaume AI. Influence of gender and helmet-mounted devices on neuromuscular activation of neck muscles during head-neck segment stabilization under GZ loading [Abstract]. Avi Space Environ Med, 2008; 79, 69.

13. Sovelius R, Oska J, Rintala R, Huhtala H, Siitonen S. Neck muscle strain when wearing helmet and NVG during acceleration on a trampoline. Avi Space Environ Med, 2008; 79,
112–116.

14. Cho AA, Clark JB, Rupert AH. Visually triggered migraine headaches affect spatial orientation and balance in a helicopter pilot. Avi Space Environ Med, 1995; 66, 353–358.

Acknowledgement   Grateful thanks to all those who responded to the query on NVG and Neck pain on PPRuNe.  Image courtesy Wikipedia Commons.

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