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Introduction: Night vision goggles (NVG) are linked to increased neck muscle activation and pain. Counterweights (NVGcw) are hypothesized to mitigate these effects. The purpose of this study was to investigate the muscular response to varying helmet loads and postures., Methods: Volunteering from a representative squadron were 16 male helicopter aviators (pilots, N = 9; flight engineers, N = 7). Subjects performed head movements to assume nine different postures (three directions: left, center, and right, at three different levels: down, level, and up) with four different head loads (no helmet; helmet only; NVG; and NVGcw) in randomized order. Subjects were provided real time visual guidance and feedback while assuming the appropriate posture in a cockpit seat in a laboratory setting. Neck muscle activation was assessed with electromyography (EMG) of four different muscle groups, bilaterally, including the sternocleidomastoid, splenius capitis, and mid and lower trapezius., Results: Two- to fourfold increases in muscle activation were observed in postures to the left (down, level, and up) while subjects wore either the NVG or NVGcw as compared to the baseline of no helmet. This was most prevalent in smaller muscle groups (i.e., the sternocleidomastoid and splenius capitis) as compared to larger muscle groups (i.e., the mid and lower trapezius)., Discussion: The use of NVGcw did not decrease neck muscle activity as compared to NVG only, particularly when the head posture moved the field of view below the horizon. This suggests interventions to decrease neck muscle activity and fatigue in military helicopter aircrew using NVG should focus on task specific guidelines with respect to countermeasures.

Introduction: To address the high prevalence of neck dysfunction in helicopter aircrew, a 12-wk training program was designed to examine the effects on neck muscular strength and endurance., Methods: Subjects were recruited from Canadian Forces (CF) helicopter aircrew and randomized into either a neck coordination training program (CTP; N = 10), an endurance training program (ETP; N = 11), or a nontreatment control (CON; N = 8). Baseline assessments determined maximal voluntary contraction (MVC) strength and endurance capacity using a submaximal contraction to fatigue at 70% of their MVC for extension, flexion, and left (Ltflx) and right (Rtflx) lateral flexion. The ETP subjects performed dynamic contractions at 30% of their MVC in the four testing directions using a head harness and Thera-band tubing. The CTP consisted of exercises that focused on strengthening the deep cervical musculature using the mass of the head as resistance and progressing to exercises that incorporated the superficial cervical muscles., Results: Post-intervention, the ETP achieved the only statistically significant increase in maximal force when compared to the CON (14.4%). Improved times to fatigue were achieved by the CTP for flexion (26.34 +/- 20.72 s), Ltflx (23.54 +/- 13.94 s), and Rtflx (28.72 +/- 4.88 s)., Conclusion: The provision of an ETP and CTP resulted in a positive trend toward improved maximal force and muscular endurance. The greatest improvements in endurance and strength were found for those subjects assigned to the CTP treatment. Our research demonstrates the importance of including a designed and supervised training program into the daily routine of helicopter aviators.

Introduction: Neck pain in the Canadian Forces (CF) helicopter community related to night vision goggles (NVG) use is of growing concern. This study compares symptom reports and physiological responses and provides comparison between pilots and flight engineers (FE)., Methods: Aircrew (22 pilots, 18 FE) detailed their neck pain symptoms, flight history, and fitness results. Subjects participated in isometric testing of flexion, extension, and right and left lateral flexion of the cervical spine that included maximal voluntary contraction (MVC) force and 70% MVC endurance trials. Cervical muscles were monitored with electromyography (EMG) and near-infrared spectroscopy (NIRS) and ratings of perceived exertion (RPE) were collected., Results: Of the aircrew, 53% reported neck pain. No significant differences were observed between pilots and FE with respect to frequency of reporting pain. MVC results were found to differ when extension was compared to flexion and when left flexion was compared to right flexion. Time-to-fatigue (TTF) results were obtained and no significant differences were found between groups. EMG assessment of normalized median frequency indicated fatigue onset while NIRS results changed from baseline for most variables during the time-to-fatigue trials., Discussion: Neck pain in Canadian Forces helicopter crewmembers continues to be an occupational concern. No significant differences between FE and pilot results were found, suggesting that the cause of the pain is likely something common to both aircrew during flight.

Unlabelled: Neck pain and muscle function in aircrew have received considerable attention. We hypothesized normalized electromyography (EMG) frequency would provide insight into appropriate methods to assess muscle fatigue in helicopter aircrew., Methods: 40 helicopter aircrew performed isometric testing that included maximal voluntary contractions (MVC) and 70% MVC endurance protocols of extension, flexion, and left and right lateral flexion for cervical muscles. Bilateral muscle activity in the splenius capitis, sternocleidomastoid, and upper trapezius was monitored with EMG. Normalized mean EMG frequency was calculated for each muscle at the start and end of the 70% MVC trials to determine which muscles fatigued and limited force maintenance during each isometric movement., Results: For extension, the left and right splenius capitis fatigued by approximately 21-22% (p < 0.01); for flexion, the left and right sternocleidomastoid fatigued by approximately 11-14% (p < 0.01); for right flexion, the right sternocleidomastoid fatigued by approximately 15% (p < 0.01); for left flexion, the left spenus capitis and left sternocleidomastoid fatigued by approximately 7.2% (p = 0.02) and approximately 11.2% (p = 0.03), respectively; in no trials did the trapezius muscles display fatigue as measured by EMG., Conclusion: The smaller agonist muscles were the most susceptible to fatigue during submaximal isometric endurance movements in the cervical muscles of helicopter aircrew.

Introduction: Documented neck strain among military helicopter aircrew is becoming more frequent and many militaries use helicopters that provide pilots with the option of sitting in the left or right cockpit seat during missions., Purpose: The purpose of this study was to use near infrared spectroscopy (NIRS) to investigate the physiological changes in trapezius muscle oxygenation and blood volume during night vision goggle (NVG) flights as a function of left and right cockpit seating., Methods: There were 25 pilots who were monitored during NVG flight simulator missions (97.7 +/- 16.1 min). Bilateral NIRS probes attached to the trapezius muscles at C7 level recorded total oxygenation index (TOI, %), total hemoglobin (tHb), oxyhemoglobin (Hbo2), and deoxyhemo-globin (HHb)., Results: No significant differences existed between variables for pilots seated in the right cockpit seat as compared with the pilots seated in the left cockpit seat in either trapezius muscle (pTOI = 0.72; ptHb = 0.72; pHbo2 = 0.57; pHHb = 0.21)., Conclusion: Alternating cockpit seats on successive missions is not a means to decrease metabolic stress for helicopter pilots using NVG. This suggests that cockpit layout and location of essential instruments with respect to the horizontal and the increased head supported mass of the NVG may be important factors influencing metabolic stress of the trapezius muscle.