James C. Croll

Prefrontal cortex oxygenation during incremental exercise in chronic fatigue syndrome

This study examined the effects of maximal incremental exercise on cerebral oxygenation in chronic fatigue syndrome (CFS) subjects. Furthermore, we tested the hypothesis that CFS subjects have a reduced oxygen delivery to the brain during exercise. Six female CFS and eight control (CON) subjects (similar in height, weight, body mass index and physical activity level) performed an incremental cycle ergometer test to exhaustion, while changes in cerebral oxy‐haemoglobin (HbO2), deoxy‐haemoglobin (HHb), total blood volume (tHb = HbO2 + HHb) and O2 saturation [tissue oxygenation index (TOI), %)] was monitored in the left prefrontal lobe using a near‐infrared spectrophotometer. Heart rate (HR) and rating of perceived exertion (RPE) were recorded at each workload throughout the test. Predicted VO2peak in CFS (1331 ± 377 ml) subjects was significantly (P ≤ 0·05) lower than the CON group (1990 ± 332 ml), and CFS subjects achieved volitional exhaustion significantly faster (CFS: 351 ± 224 s; CON: 715 ± 176 s) at a lower power output (CFS: 100 ± 39 W; CON: 163 ± 34 W). CFS subjects also exhibited a significantly lower maximum HR (CFS: 154 ± 13 bpm; CON: 186 ± 11 bpm) and consistently reported a higher RPE at the same absolute workload when compared with CON subjects. Prefrontal cortex HbO2, HHb and tHb were significantly lower at maximal exercise in CFS versus CON, as was TOI during exercise and recovery. The CFS subjects exhibited significant exercise intolerance and reduced prefrontal oxygenation and tHb response when compared with CON subjects. These data suggest that the altered cerebral oxygenation and blood volume may contribute to the reduced exercise load in CFS, and supports the contention that CFS, in part, is mediated centrally.

Cervical Cancer Screening Practices among University Women

OBJECTIVE To assess predictors of young womens intentions to be screened for cervical cancer. DESIGN A descriptive, correlational, cross-sectional study using the Theory of Planned Behavior (TPB). PARTICIPANTS A total of 904 young women (mean age=20.7 years; SD=1.77) participated in an online cervical cancer screening survey. METHOD A web-based survey (WebCT) was used to survey young women, 25 years of age or less, attending a university in eastern Canada. Descriptive, correlational, and logistic regression statistics were calculated. RESULTS Findings indicated that social norms (perceptions about whether or not people close to them think Pap screening is important) and perceived behavioral control (perceptions about personal resources or barriers to receiving a Pap test) were significantly related to young womens intentions to be screened. CONCLUSION Strategies to promote cervical cancer screening among young university women need to recognize the impact of social norms and perceived barriers on Pap screening intentions in this population.

Measuring Neuromuscular Fatigue in Cervical Spinal Musculature of Military Helicopter Aircrew

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.

Physiological Effects of Night Vision Goggle Counterweights on Neck Musculature of Military Helicopter Pilots

UNLABELLED Increased helmet-mounted mass and specific neck postures have been found to be a cause of increased muscular activity and stress. However, pilots who use night vision goggles (NVG) frequently use counterweight (CW) equipment such as a lead mass that is attached to the back of the flight helmet to provide balance to counter the weight of the NVG equipment mounted to the front of the flight helmet. It is proposed that this alleviates this stress. However, no study has yet investigated the physiological effects of CW during an extended period of time during which the pilots performed normal operational tasks. METHODS Thirty-one Canadian Forces pilots were monitored on consecutive days during a day and a NVG mission in a CH-146 flight simulator. Near infrared spectroscopy probes were attached bilaterally to the trapezius muscles and hemodynamics, i.e., total oxygenation index, total hemoglobin, oxyhemoglobin, and deoxyhemoglobin, were monitored for the duration of the mission. Pilots either wore CW (n = 25) or did not wear counterweights (nCW, n = 6) as per their usual operational practice. RESULTS Levenes statistical tests were conducted to test for homogeneity and only total oxygenation index returned a significant result (p < or = 0.05). For the near infrared spectroscopy variables, significant differences were found to exist between CW and nCW pilots for total hemoglobin, deoxyhemoglobin, and oxyhemoglobin during NVG flights. The CW pilots displayed less metabolic and hemodynamic stress during simulated missions as compared to the nCW pilots. CONCLUSION The results of this study would suggest that the use of CW equipment during NVG missions in military helicopter pilots does minimize the metabolic and hemodynamic responses of the trapezius muscles.

Helicopter cockpit seat side and trapezius muscle metabolism with night vision goggles.

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.

Neck Pain and Muscle Function in a Population of CH-146 Helicopter Aircrew

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.

A predictive logistic regression equation for neck pain in helicopter aircrew.

INTRODUCTION While many studies have investigated neck strain in helicopter aircrew, no one study has used a comprehensive approach involving multivariate analysis of questionnaire data in combination with physiological results related to the musculature of the cervical spine. METHODS There were 40 aircrew members who provided questionnaire results detailing lifetime prevalence of neck pain, flight history, physical fitness results, and physiological variables. Isometric testing data for flexion (Flx), extension (Ext), and right (RFlx) and left (LFlx) lateral flexion of the cervical spine that included maximal voluntary contraction (MVC) force and submaximal exercise at 70% MCV until time-to-fatigue (TTF) was also collected. Muscles responsible for the work performed were monitored with electromyography (EMG) and near-infrared spectroscopy (NIRS) and the associated ratings of perceived exertion (RPE) were collected simultaneously. Results were compiled and analyzed by logistic regression to identify the variables that were predictive of neck pain. RESULTS While many variables were included in the logistic regression, the final regression equation required two, easy to measure variables. The longest single night vision goggle (NVG) mission (NVGmax; h) combined with the height of the aircrew member in meters (m) provided an accurate logistic regression equation for approximately one-half of our sample (N = 19). Cross-validation of the remaining subjects (N = 21) confirmed this accuracy. CONCLUSION Our regression equation is simple and can be used by global operational units to provide a cursory assessment without the need for acquiring specialized equipment or training.

Posture and Helmet Load Influences on Neck Muscle Activation.

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.