The Effects of Chronic Shiftwork and Heat Stress on Static and Dynamic Postural Balance in Firefighters: a Pilot Study
Abstract No:
1706
Abstract Type:
Student Poster
Authors:
R Zeiler1, A Bhattacharya1
Institutions:
1University of Cincinnati, Cincinnati, OH
Presenter:
Rachel Zeiler
University of Cincinnati
University of Cincinnati
Faculty Advisor:
Dr. Amit Bhattacharya, PhD
University of Cincinnati
University of Cincinnati
Description:
Firefighters are subjected to a range of hazards every day; the cumulative effect of these hazards has not been well-defined in research. In this study, we investigate the impact of chronic exposure to shiftwork and heat stress on postural balance and gait functions using wearable sensor technology. This is a sub-analysis of an on-going larger study and does not include the results from the functional MRI (fMRI) or immune biomarker analysis aspects.
Situation/Problem:
During their job, firefighters are exposed to a variety of chemical, safety, ergonomic, and physical hazards. Although acute exposure to chemical or safety hazards may be life threatening, chronic shiftwork and heat stress may also have long-lasting adverse health effects [1, 5-6, 9]. Firefighters regularly perform physically demanding work in high heat environments; the duration of exposure is often unpredictable. Acute effects of heat stress have been studied following a shift or live-burn training, but the chronic impact on balance and cognitive decision making has never been evaluated [1-3].
Because of the urgency of the job, most firefighters work a 24 hour on/48 hour off schedule and average 60 hours/week [4]. During the extended shift period (up to 48 hours), a firefighter's sleep may be frequently interrupted for emergencies. Poor sleep quality and interrupted sleep has been associated with decreased cognitive function, reduced immune function, and increased postural instability, all which may leave a firefighter vulnerable to workplace accidents and illnesses [1, 5-7]. In this study we proposed to evaluate the functional balance outcomes in firefighters with a long history of work experience as a firefighter. Our hypothesis is that chronic cumulative exposures to heat stress and shiftwork as a firefighter will increase postural instability and increase the risk of falls.
Because of the urgency of the job, most firefighters work a 24 hour on/48 hour off schedule and average 60 hours/week [4]. During the extended shift period (up to 48 hours), a firefighter's sleep may be frequently interrupted for emergencies. Poor sleep quality and interrupted sleep has been associated with decreased cognitive function, reduced immune function, and increased postural instability, all which may leave a firefighter vulnerable to workplace accidents and illnesses [1, 5-7]. In this study we proposed to evaluate the functional balance outcomes in firefighters with a long history of work experience as a firefighter. Our hypothesis is that chronic cumulative exposures to heat stress and shiftwork as a firefighter will increase postural instability and increase the risk of falls.
Methods:
Twenty-one subjects were recruited from the Greater Cincinnati Area between the ages of 30-45 years of age that had worked as a volunteer, part-time, or full-time firefighter for at least one year. All participating subjects gave informed consent and completed shiftwork questionnaires for descriptive statistics.
Instrumentation: A force platform (AMTI, model OR6-6-1000, Watertown, MA) is used during static postural balance testing to detect postural instability by quantifying changes in center of pressure (CP) movement patterns during a 30-second test. Five inertial sensors (BioSensics LEGSys+TM Newton, MA) equipped with a 3-D gyroscope and accelerometer were attached to the chest, thigh, and shin of each firefighter to measure linear acceleration and angular velocity during static and dynamic postural stability testing. A custom software (bas_v1.35) was used to quantify the measured variables from the sensors and force platform. The software transforms the measurements from the LEGSys sensors to derive linear and angular acceleration, displacement, and velocity. The force platform measures are converted into linear acceleration, displacement, and velocity [8].
Static testing: Firefighters stand on a force platform and undergo 30 second tests using four test conditions: (1) eyes open on two legs, (2) eyes closed on two legs, (3) eyes open on one leg, and (4) eyes closed on one leg. The conditions are designed to challenge the sensory afferents associated with balance. For example, two-legs, eyes closed tests challenge the proprioceptive and vestibular systems and one-leg, eyes open tests challenge the visual and proprioceptive system. If at any time, the firefighter loses balance or has to put their foot down during a one-legged test, the test is stopped and recorded as "Fall"; the test is not repeated. Force platform and LEGSys sensor data are processed and analyzed separately.
Dynamic testing: Firefighters performed an instrumented timed-up-and-go (iTUG) test. During the iTUG test, the firefighters are instructed to stand up from a chair, walk at a normal pace seven meters across the room, turn around a cone, walk back to the chair, and sit down. Firefighters also perform an iTUG with dual task: the firefighter is asked to continuously subtract by three from a given number throughout the duration of the iTUG test. The dual task is designed to test the firefighter's motor function while performing a mentally stimulating task challenging the cognitive executive function. The measurements from the iTUG test are analyzed as gait and gait phase plane [1].
Statistical analysis:
Firefighters were separated into two groups based on years of experience as a firefighter (Group 1 = ≤5 yrs, Group 2 = > 5 yrs). A custom program, bas_v1.35 was used to analyze force platform and sensor data. R Studio_v1.2.1335 was used to design classification trees for each analysis.
Instrumentation: A force platform (AMTI, model OR6-6-1000, Watertown, MA) is used during static postural balance testing to detect postural instability by quantifying changes in center of pressure (CP) movement patterns during a 30-second test. Five inertial sensors (BioSensics LEGSys+TM Newton, MA) equipped with a 3-D gyroscope and accelerometer were attached to the chest, thigh, and shin of each firefighter to measure linear acceleration and angular velocity during static and dynamic postural stability testing. A custom software (bas_v1.35) was used to quantify the measured variables from the sensors and force platform. The software transforms the measurements from the LEGSys sensors to derive linear and angular acceleration, displacement, and velocity. The force platform measures are converted into linear acceleration, displacement, and velocity [8].
Static testing: Firefighters stand on a force platform and undergo 30 second tests using four test conditions: (1) eyes open on two legs, (2) eyes closed on two legs, (3) eyes open on one leg, and (4) eyes closed on one leg. The conditions are designed to challenge the sensory afferents associated with balance. For example, two-legs, eyes closed tests challenge the proprioceptive and vestibular systems and one-leg, eyes open tests challenge the visual and proprioceptive system. If at any time, the firefighter loses balance or has to put their foot down during a one-legged test, the test is stopped and recorded as "Fall"; the test is not repeated. Force platform and LEGSys sensor data are processed and analyzed separately.
Dynamic testing: Firefighters performed an instrumented timed-up-and-go (iTUG) test. During the iTUG test, the firefighters are instructed to stand up from a chair, walk at a normal pace seven meters across the room, turn around a cone, walk back to the chair, and sit down. Firefighters also perform an iTUG with dual task: the firefighter is asked to continuously subtract by three from a given number throughout the duration of the iTUG test. The dual task is designed to test the firefighter's motor function while performing a mentally stimulating task challenging the cognitive executive function. The measurements from the iTUG test are analyzed as gait and gait phase plane [1].
Statistical analysis:
Firefighters were separated into two groups based on years of experience as a firefighter (Group 1 = ≤5 yrs, Group 2 = > 5 yrs). A custom program, bas_v1.35 was used to analyze force platform and sensor data. R Studio_v1.2.1335 was used to design classification trees for each analysis.
Results / Conclusions:
RESULTS
Demographics: The study participants consisted of twenty-one, male, part-time and full-time firefighters. The firefighters were separated into two groups based on years of experience as a firefighter (Group 1= ≤ 5 yrs; Group 2= > 5yrs).
Static balance:
There was no significant difference between the static postural outcomes, but there were still falls during static testing and those with more work experience had, on average, more falls.
Dynamic testing:
Gait Analysis:
Peak linear acceleration and angular velocity around the turn were classifying variables for both single and dual task, but there was no significant difference between gait outcomes.
Gait Phase Plane Analysis:
The classification tree determined fourteen classifying variables for single-task gait phase plane. Four of those variables were significantly different between the two experience groups, AP Displacement vs ML Displacement Percent Out Mean, ML Displacement vs ML Velocity Length Total, ML Displacement vs ML Acceleration Area, and ML Displacement vs ML Acceleration Length Total (ML = medial-lateral, AP = anterior-posterior).
The classification tree determined thirteen classifying variables for dual-task gait phase plane. Three of those variables were significantly different between the two experience groups, ML Displacement vs ML Velocity Length Total, ML Displacement vs ML Acceleration Length Total, ML Displacement vs ML Acceleration Length Variance.
CONCLUSION
Static balance – Sway Phase Plane
While Singh, et al. provided evidence that acute exposure to heat stress increased the combined stability parameter during static testing, our results showed that cumulative chronic exposure to firefighting and shiftwork detrimentally influenced the fall status without any acute heat stress [1]. Decreased static postural stability in firefighters has been observed after performing a 24-hour shift, but the chronic effects have never been assessed until now [9].
Dynamic balance – Gait Analysis and Gait Phase Plane
Results from our study demonstrated the firefighters with a longer work history (Group 2 vs Group 1) of fighting fires and shiftwork, experienced decrement in their postural instability during performance of the iTUG under single and dual task conditions. Park et al. showed that acute fatigue from firefighting in heat stress situations effected gait parameters and increased the risk of tripping over obstacles [10]. Sleep deprivation from chronic shiftwork has been shown to impact neurocognitive functions which may also put firefighters at risk for accidents at work [3, 5].
The methods of this study should be replicated in a larger study to confirm these findings.
Demographics: The study participants consisted of twenty-one, male, part-time and full-time firefighters. The firefighters were separated into two groups based on years of experience as a firefighter (Group 1= ≤ 5 yrs; Group 2= > 5yrs).
Static balance:
There was no significant difference between the static postural outcomes, but there were still falls during static testing and those with more work experience had, on average, more falls.
Dynamic testing:
Gait Analysis:
Peak linear acceleration and angular velocity around the turn were classifying variables for both single and dual task, but there was no significant difference between gait outcomes.
Gait Phase Plane Analysis:
The classification tree determined fourteen classifying variables for single-task gait phase plane. Four of those variables were significantly different between the two experience groups, AP Displacement vs ML Displacement Percent Out Mean, ML Displacement vs ML Velocity Length Total, ML Displacement vs ML Acceleration Area, and ML Displacement vs ML Acceleration Length Total (ML = medial-lateral, AP = anterior-posterior).
The classification tree determined thirteen classifying variables for dual-task gait phase plane. Three of those variables were significantly different between the two experience groups, ML Displacement vs ML Velocity Length Total, ML Displacement vs ML Acceleration Length Total, ML Displacement vs ML Acceleration Length Variance.
CONCLUSION
Static balance – Sway Phase Plane
While Singh, et al. provided evidence that acute exposure to heat stress increased the combined stability parameter during static testing, our results showed that cumulative chronic exposure to firefighting and shiftwork detrimentally influenced the fall status without any acute heat stress [1]. Decreased static postural stability in firefighters has been observed after performing a 24-hour shift, but the chronic effects have never been assessed until now [9].
Dynamic balance – Gait Analysis and Gait Phase Plane
Results from our study demonstrated the firefighters with a longer work history (Group 2 vs Group 1) of fighting fires and shiftwork, experienced decrement in their postural instability during performance of the iTUG under single and dual task conditions. Park et al. showed that acute fatigue from firefighting in heat stress situations effected gait parameters and increased the risk of tripping over obstacles [10]. Sleep deprivation from chronic shiftwork has been shown to impact neurocognitive functions which may also put firefighters at risk for accidents at work [3, 5].
The methods of this study should be replicated in a larger study to confirm these findings.
Primary Topic:
Ergonomics
Secondary Topics:
Changing Workforce Demographics/Environment/Total Worker Health
Sensor Technologies
Co-Authors
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Acknowledgements and References
List any additional people who worked on the project or provided guidance and support along with details on the role they played in the research. (Please include first name, last name, organization, city, state and country).
REFERENCES
1. Singh, U., Mani, A., James, K., Rao, M.B., Bhattacharya, A., Effects of Heat Exposure from Live-Burn Fire Training on Postural Stability of Firefighters. Ergonomics International Journal, 2019. 3(4).
2. Nybo, L., N.H. Secher, and B. Nielsen, Inadequate heat release from the human brain during prolonged exercise with hyperthermia. J Physiol, 2002. 545(2): p. 697-704.
3. Goel, N., et al., Neurocognitive consequences of sleep deprivation. Semin Neurol, 2009. 29(4): p. 320-39.
4. CDC, Working Hours, Sleep, & Fatigue Forum. 2019.
5. Barger, L.K., et al., Common sleep disorders increase risk of motor vehicle crashes and adverse health outcomes in firefighters. J Clin Sleep Med, 2015. 11(3): p. 233-40.
6. Nagai, M., et al., Effects of fatigue on immune function in nurses performing shift work. J Occup Health, 2011. 53(5): p. 312-9.
7. Kucharczyk, E.R., K. Morgan, and A.P. Hall, The occupational impact of sleep quality and insomnia symptoms. Sleep Med Rev, 2012. 16(6): p. 547-59.
8. Dicesare, C., Balance Analysis Suite User Guide. 2020: University of Cincinnati.
9. Sobeih, T.M., et al., Postural balance changes in on-duty firefighters: effect of gear and long work shifts. J Occup Environ Med, 2006. 48(1): p. 68-75.
10. Park, K., et al., Assessing gait changes in firefighters due to fatigue and protective clothing. Safety Science, 2011. 49(5): p. 719-726.
Practical Application
How will this help advance the science of IH/OH?
This study also highlights the use of wireless, inertial sensors in laboratory studies. The LEGSys sensors used were able to detect significant differences in the functional outcomes between two groups of experienced and inexperienced firefighters.