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A pain in the neck—causes in helicopter and fighter pilots

Chronic and acute neck pain among pilots can affect the readiness and effectiveness of service men and women who take to the skies on a regular basis. Find out what is being done about the increasing occurrence of neck pain among military pilots of helicopters and fighter jets.

B.L.U.F.

Neck pain in military pilots, particularly helicopter and fighter jet pilots, is a major concern. Conditions inherent in flying helicopters and jets put these pilots (and crew) at a greater risk for developing neck pain due to misaligned postures, the use of additional equipment on their helmets, and exposure to high G-forces. Effectiveness and readiness are compromised if a pilot can’t fly because of pain. Pilots sometimes forego medical treatment for fear of being grounded or losing their flight status and, as a result, pain is left untreated.

Exercise programs specifically for strengthening the neck area can be helpful in preventing pain. “G-warmup” maneuvers can also be beneficial to prepare a fighter pilot for high G-forces. Military researchers are looking at improving and updating the ergonomics of aircraft seats and cockpits, as well as helmet fit. In the meantime, see your doctor if your neck pain doesn’t improve with rest and basic at-home treatments. And for more information, read HPRC’s InfoReveal.

InfoReveal

Both international and American studies have found that a significant and increasing number of helicopter and fighter pilots suffer from neck (and other) pain as a result of their occupation. Many pilots seek out civilian rather than military medical treatment to avoid being grounded or losing their flight status. Others self-medicate with high doses of over-the-counter remedies such as ibuprofen, which can cause other health problems when taken long term.

Neck pain, usually associated with muscle stiffness and soreness, can be a result of several factors, although the impact of each depends on the type of pilot (helicopter versus fighter). However, seat postures, G-forces, high-risk head movements, whole-body vibration, and helmet-mounted equipment and fit play major roles in the development of pilot and aircrew neck pain. Other risk factors include age, flight hours, duration of flights, decreased muscle strength, and the onset rate of G-forces.

What We Know

Three major factors contribute to neck pain among military pilots: posture (ergonomics), helmets, and vibration. Most current helicopter cockpits were designed to reduce injuries from the hard landings and vertical crashes that were common during the Vietnam War. This design forces helicopter pilots to assume a unique position, often referred to as “helo-hunch,” a misaligned posture in which a pilot’s trunk is curved forward and slightly rotated. Ergonomic concerns for fighter pilots are more related to G-forces and neck movements associated with various maneuvers. “Checking six,” or turning to look towards the tail of the aircraft, requires extreme neck rotation that uses relatively weak muscles in the neck. Chronic exposure to such postures puts pilots at greater risk for neck pain.

The way a helmet fits, in addition to the equipment added to it—night vision goggles (NVG) and other helmet-mounted displays (HMDs)—can contribute to neck pain. The equipment mounted on a helmet changes its weight distribution on the head and neck in a way that can impede vision and cause irritation that forces the pilot to use more awkward neck positions.

Whole-body vibration, especially in helicopters, transmits mechanical vibration from the aircraft throughout the bodies of its occupants, but primarily to the pilot. The amount of whole-body vibration (WBV) a pilot experiences, combined with other factors such as posture and helmet fit, further increases the risk for neck pain or worsens existing pain.

Concerns

Pilots are not the only military personnel at risk for neck pain. Those who are confined to small spaces, with poor seating posture, and/or are exposed to WBV (e.g., tanks and high-speed marine craft) for a long period of time may also experience symptoms.

It is important to recognize symptoms of potentially serious neck pain and seek medical advice early on. Avoid self-medicating with high doses of over-the-counter drugs such as ibuprofen, which can lead to other health problems if taken for a long time. Only medical treatment can address whether the pain is easily treatable or a symptom of a more serious chronic condition.

Debrief (Military Relevance)

Several studies strongly recommend the use of “G-warm up” and neck stretching techniques prior to flying. Other research suggests that neck stabilization and strengthening exercise routines may also improve neck pain and range of motion (ROM). While these techniques have not proven to be effective for all pilots, some individuals have had success with personalized neck strengthening and training regimens.

Researchers also have recommended equipment-related solutions that are undergoing military scrutiny and development, such as the redesign of cockpits and pilot seating, inner lining of helmets, and seat pads to reduce transmission of mechanical vibration to aircraft occupants.

For more details and in-depth information on neck pain in military pilots and aircrew, see HPRC’s research brief “Neck Pain Among Pilots and Aircrew.”

Research Summary

Key Points

  • An increasing number of helicopter and fast-jet military pilots are reporting neck, back, and leg pain related to their flight experience.
  • Chronic neck pain can be related to helmet fit, use of night vision goggles (NVG), seat posture, vibrations, flight duration, frequency of exposure, and physical conditioning.
  • Pilots and aircrew frequently do not seek medical attention for chronic or acute neck pain for fear of losing flight status or being grounded.
  • Measures to prevent neck pain in pilots include changes in the ergonomics of aircraft cockpits and helmets, as well as the implementation of pre- and post-flight exercise programs for the neck and upper body.

Background

Neck pain in military pilots and crew is a growing, international aeromedical concern. Several surveys in Canada, Australia, and Sweden investigating neck pain have found an alarmingly high rate of pain, sometimes chronic, in both helicopter and fast jet pilots.1-3 In 2010–2011, the DoD conducted an online survey of nearly 10,000 U.S. helicopter pilots and aircrew to evaluate self-reported neck, back, and leg pain related to flight.4 Consistent with other studies, approximately 85% of U.S. military helicopter pilots and aircrew suffered some form of neck, back, or leg pain that they believed to be associated with flying. 25% of in-service and 23% of post-service responders to the DoD survey experienced neck pain or discomfort more than once per week while flying, and 62% of the in-service population sampled avoided seeking medical attention or sought out treatment from civilian doctors for fear of being grounded or losing their flight status. The bottom line is that neck (and back) pain impacts mission readiness and effectiveness when air crew (especially pilots) are distracted by the pain and fatigue, cancel or miss their flights, take time out to seek medical treatment, lose flight status, are temporarily grounded, require surgery, and/or end their flying careers.

Neck pain is usually associated with muscle stiffness or soreness, possibly due to weakness and/or fatigue.5 The etiology of neck pain differs between helicopter and fast-jet pilots, although both experience chronic pain and even acute injury, as well as degenerative changes of the cervical vertebrae that can lead to chronic neck pain. Sitting postures, gravitational forces (G- forces), whole-body vibrations, high-risk head movements, and helmet fit, weight, and equipment are factors that affect both types of pilots but vary between them.

Acute and chronic neck pain—including cervical vertebral fractures and ligament tears6,7—is more frequent among fast-jet pilots and aircrew and likely relates to high G-forces and non-neutral neck positions experienced during performance maneuvers. This neck pain in U.S. fighter pilots has been correlated with pilot age, flight hours, G-force level and onset rate, decreased muscle strength, number of repeated exposures, duration of exposure, and duration of rest between exposures.8 The risk of neck injury in F-16 pilots has been found to increase 6.9% per 100 hours of flying time.9

Whole-body vibration (WBV), use of night-vision goggles (NVG), helmet-mounted displays (HMD), and poor cockpit sitting posture—“helo hunch”—are significant factors among helicopter pilots and aircrew.5

Myths/Claims

In addition to the external risk factors for flight-related neck pain such as pilot equipment and ergonomic factors, there are two hypotheses that attempt to explain the underlying physiological processes that can contribute to neck pain. The Cinderella Hypothesis proposes that the continuous contraction of small, type-I muscle fibers during low-intensity, long-duration tasks (as experienced by helicopter pilots) can increase risk for future damage to these muscles. The Nitric Oxide Ratio Hypothesis suggests that inhibition of the terminal enzyme in the mitochondrial electron transport chain—cytochrome oxidase—reduces the ability of the cells to aerobically generate adenosine triphosphate (ATP). Muscle cells then must rely on anaerobic glycolysis to produce energy, which results in lactic acid. Lactic acid may activate certain neural fibers, which ultimately leads to pain.5

Facts and Evidence

Several factors play a role in the onset of neck pain in helicopter and fast-jet pilots, as mentioned above. While some of these may influence each type of pilot to a different extent, the combination of posture, ergonomics, helmet fit and equipment, and exposure to whole-body vibration for extended periods of time can lead to chronic pain and, potentially, disability.

Posture and ergonomics

Postural concerns for fast-jet pilots are primarily related to the head movements required during aerial maneuvers. Normal cervical spine movement consists of flexion, extension, lateral bending, and rotation of the head and neck. High G-forces compound the effects of these movements, adding strain and stress to the neck and resulting in compressive, tensile, and shear components. However, the most common adverse effects are associated with compression of the cervical spine as a result of positive forces acting downward (+Gz ; i.e., toward the feet). High-performance flying and aerial maneuvers can exert extremely intense forces, sometimes greater than +9Gz. Forces greater than +4Gz have been associated with potential neck injury, and most surveys report onset of pain between +4 and +9Gz.10-12 Research has also identified certain neck movements in high G-force conditions as high risk for neck pain: neck rotation beyond 35°, lateral bending, extension (i.e., looking up) beyond 30°, flexion (i.e., looking down) beyond 15°, and “checking six.” This last movement—“checking six,” or turning to look towards the tail of the aircraft—can present the highest risk. It requires maximal neck rotation and maximal recruitment of muscle motor units. Each of these movements creates significant stress by requiring substantial forces from supporting tissues to stabilize the head and neck. However, the neck rotator muscles generate the least isometric force of all the neck muscles.13 In addition to neck rotation, the pilot’s neck is also in flexion or extension and lateral bending, a combination that often leads to acute neck injuries.14 The seat angle of fast jets—with the addition of high +Gz forces—has an effect on subjective discomfort and neck pain in their pilots. One study found that differences in cervical spine biomechanics in F-16 aircraft with a 30° reclined seat required an additional 15° forward flexion of the neck to maintain normal direction of the pilot’s gaze.14

Due to the design of helicopter cockpits, pilots are forced into a misaligned posture, also known as “helo-hunch,” which has also been cited as a cause for low-back pain.15 The current seating system in helicopter cockpits was originally designed for “crashworthiness” to reduce injuries from hard landings or the flat-vertical crashes common in the Vietnam era. Pilots sit in vertically adjustable seats installed at a fixed reclined angle of 15°.4 The pilot must often bend forward to see out of the cockpit, with reduced or absent lordosis (normal curvature of the lower back) and the trunk slightly rotated to the left to reach pitch levers and controls. This posture forces the lower cervical spine into flexion and the upper cervical spine into extension so this portion of the spine is continuously activated. Helo-hunch low-back pain symptoms and strain can be aggravated by the addition of a helmet and/or whole-body vibration. One of the major recommendations to come out of the 2011 DoD study was that current seating systems should be updated and that modifications should focus on using state-of-the-art materials and ergonomically sound engineering, with the use of non-traditional and creative solutions.

Helmet fit and equipment

Helmet fit is another major factor in reported neck pain among pilots and aircrew. Helmets have evolved beyond simply protecting the head to providing a mount for the advanced technology required for today’s missions. Pilots and aircrew rely on NVG, HMD, and even counterweights (CW), which add to the weight of the helmet and change its weight distribution on the head and neck. The forward weight of HMD becomes a factor at high G-forces, impeding vertical eye coordination and peripheral vision which and forcing the fast-jet pilot into even more awkward neck positions during certain maneuvers. Proper helmet fit and a redesigned inner lining can decrease the feeling of helmet gliding, neck load, pressure points, and irritation/distraction, increasing overall comfort and reducing neck pain during flight.16 Research also has found significant differences in postures and neck loads between night and day flights: During night flights requiring the use of NVG, compression forces on the neck were found to be greater, and a pilot’s neck was spent mildly flexed 74% of the time, compared to 43% of the time during day flights, when NVG were not worn.17 And one study demonstrated the extent to which the use of NVG increased the rate of neck pain in helicopter pilots when combined with longer duration flights: Helicopter pilots who flew more than 700 hours using NVG had an 80% likelihood of developing neck pain, compared with 53% for aircrew with fewer than 200 hours with NVGs.18

Whole-body vibration

WBV is defined as “the mechanical vibration that, when transmitted to the whole body, entails risk to the health and safety of workers, in particular lower-back morbidity and trauma of the spine.”19 WBV is experienced by the pilot (primarily from the seat) and by the crew throughout the helicopter, and intensities vary depending on a crew member’s position in the aircraft. The normal vibration levels of fixed-wing aircrafts are lower than those of helicopters, which vibrate at frequencies related to the speeds of revolution of the main rotor (4-11 Hz), tail rotor (30-60 Hz), and engine (110 Hz). Studies designed to quantify the effects of WBV have found that vibration frequency as low as 5 Hz can increase helmet and head displacement exponentially when vibrations are transmitted from the buttocks to the head in the seated position.20,21 However, other studies22,23 have found that WBV for most helicopter aircrew do not exceed thresholds for health risk according to international guidelines24 and did not induce muscular fatigue in crew members.18 This research suggests that WBV, in addition to posture, might increase the risk for low back pain and potentially neck pain as well. It should be noted that vibration levels do vary with every mission depending on the type of aircraft and duration of flight.

Cautions

Neck pain has been identified as a problem for pilots; however, other occupations requiring the use of helmets and NVG, confinement to small spaces with poor seated posture, or exposure to WBV (e.g., tanks25 and high-speed marine craft26)are also at risk for neck pain. It’s important to recognize the symptoms early and seek out appropriate treatment.

Use of ibuprofen for alleviation of pain is common among service members, including pilots. However, taking ibuprofen for a prolonged period of time can have other serious health consequences.27

Military Relevance

Several studies recommend a “G-warmup” and neck stretching prior to flights. Others have found significant improvements of neck pain and ROM in study groups who engage in neck stabilization and other strengthening exercise routines.28-30 However, other studies have found no protective benefit or significant differences among study subjects with and without neck pain.31,32 Other inflight techniques have also been suggested, although not proven28,29, to minimize the movement of the head during high G-force maneuvers. These include prepositioning the head prior to the onset of G-forces and “unloading” the forces on the aircraft before moving the neck. Significant decreases in neck injuries have been noted among F-16 pilots who used the unloading technique.9

According to an extensive literature review5, exercise therapy is the most common treatment modality for non-specific neck pain. Although the exact role and efficacy of exercise therapy to treat and prevent neck pain is still being studied, some research has found pilots to be successful in reducing neck pain after a six-week exercise regimen.33 Another study found that helicopter pilots least likely to suffer from neck pain were those who participated in daily aerobic exercise.18 The review mentioned above did recommend further research into the efficacy of low-resistance endurance and coordination training for both treatment and prevention of neck pain.5 The evidence for and against the effectiveness of G-warm ups and stretching is still conflicting, and there may be no one-size-fits-all solution; various exercise and training programs have shown promise, so individualized training should also be explored.28

Summary

The consequences of neck pain can affect a pilot’s concentration, interfere with safety, and decrease quality of life. Additionally, pilots may not report pain or may seek treatment from civilian doctors for fear of being grounded. Whereas the etiology for each pilot may be different, the effects of external risk factors such as helmet weight and fit, seat vibrations, and G-forces can be minimized with certain modifications, special in-flight techniques, pilot education, and perhaps future policy changes. However, preventive and treatment measures such as exercise therapy have not yet been proven to be effective for all pilots. Ample evidence exists to show that interventions are both justified and needed to eliminate the problem of neck, back, and leg pain among this military cohort.4 Future and ongoing efforts will include improving the ergonomics of the cockpit (including more ‘human-centric’ seats with vibration isolators) and the fit of helmets, promoting pre/post flight exercises, and improving flight surgeon and aircrew relationships.

References

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