Abstract
Slips and falls account for a significant number of injuries suffered by firefighters. Obesity may be a contributing factor to these slips and falls since many firefighters have become significantly heavier over the last decade. This study’s objective was to determine whether obesity places firefighters at a higher risk of slips/falls by impacting postural balance. Thirteen firefighters – 6 obese and 7 overweight/normal, had their postural balance measured over a single shift (at 12-hour intervals). Each assessment contained three specific tasks: eyes open while standing, eyes closed standing on foam, and a dynamic reach task. The firefighters wore turnout gear with and without SCBA. Obese firefighters were found to have less postural sway, particularly when their postural control systems were compromised. When standing on foam, obese firefighters reduced their sway area by 26% as compared to overweight/normal firefighters. Similarly, obese firefighters had an 18% decrease in postural sway during the reach task. In all, the results indicate obese firefighters compensated posturally, reducing the potential for external demands resulting in a slip or fall. The key issue is that the obese firefighters sampled in the current study were able to compensate under ideal situations, particularly when required to wear gear and equipment.
Keywords: Postural balance, emergency response, personal protective equipment, slips and falls
1. Introduction
Firefighters work in a very physically demanding occupation under harsh conditions including extreme heat, cold, elevated heights, slippery and unstable surfaces. Firefighters also have to wear a significant amount of protective gear which adds an additional load to the firefighter and may also impact their mobility and stability. From 1994 to 1998, slips or falls accounted for 19% of fire ground injuries [10]. In 2003, falls, slips, and jumps were the second leading cause of injury during fire ground activities, accounting for 27.6% of total injuries [11]. With high rates of injury that have continued to increase in recent years, it is necessary to understand the factors contributing to the slips and falls that cause a significant amount of injuries in firefighters.
A few studies have investigated the addition of protective gear as a cause for slips and falls among firefighters. A significant association between the use of the self-contained breathing apparatus (SCBA) and falls was found in a study by Heineman and colleagues [8]. This epidemiological study points to the addition of heavy protective equipment as impacting the postural response of firefighters. A laboratory study by Kincl and colleagues [12] also supports this notion based on the findings that wearing different protective equipment had significant impact on postural balance, particularly in the presence of muscle fatigue. In the firefighter population, Sobeih and associates [20] found that postural balance indices (e.g. sway length and sway area) decreased when SCBA and turnout gear was worn, implying an improvement in the postural stability. It was hypothesized that firefighters may have adapted their postural response through a conditional reflex that allows them to adjust to adverse conditions commonly faced by them.
Another potential contributing factor for slips and falls is the increased prevalence of firefighters with excessive weight (either overweight with Body Mass Index (BMI) > 28 kg/m2 or obese with BMI > 30 kg/m2). Several studies have found high percentages of firefighters being overweight and obese. In a study of 218 firefighters [5], the average BMI was 28.8 kg/m2 (± 4.5), with less than 20% of the firefighters having a normal bodyweight, 48% being overweight, 29.8% being obese, and 2.3% being morbidly obese. Essentially, a startling 80.1% of the firefighters were classified as being overweight, obese, or morbidly obese. Similar trends were observed in several other large studies with approximately 45 to 60% being overweight, and 30 to 40% being obese [3,9]. Thus, based on these previous studies, a significant portion of the firefighting population meets the criteria for being considered overweight or obese.
This additional body weight may place additional stress on the body or alter the postural stability response, potentially resulting in increased risk of slips and falls. One potential effect of the excessive weight would be a change in distribution of body weight that alters the ability of the firefighters to maintain postural stability, particularly under adverse conditions such as a dark smoke filled building, slippery and wet surfaces, and unstable floors. Another potential response might be similar to that noted by Sobeih and associates [20] who identified an adaptation to the increased weight of the SCBA and turnout gear. Similarly, the excessive weight may produce altered postural sway in a highly trained work population like firefighters that may allow them to maintain posture in very difficult environments. However, no research has been conducted to determine if being overweight or obese has the potential to increase the risk of slips and falls in firefighters compared to their normal weight comrades and whether adaptations may be occurring for this at risk population. Therefore, the objective of this study was to determine the impact of excessive body weight (obese) on the postural balance of firefighters.
2. Methods
2.1. Participants
Thirteen firefighters at the Sycamore Township Fire Department, Cincinnati, Ohio (Station 92) volunteered for this study. Of these 13 firefighters, 6 of them were obese (body mass index (BMI) > 30 kg/m2) while the remaining 7 were classified into overweight (4 with BMI between 28 and 30) and normal (3 with BMI below 28 kg/m2). Table 1 provides a summary of the demographic variables. At the start of the study, all participants were provided a summary of the study procedures, read and signed a consent form approved by the University of Cincinnati Institutional Review Board. A short health questionnaire was completed to screen the participants for any history of any of the following conditions that may affect their balance: dizziness, tremors, alcoholism, vestibular disorders, neurological disorders, diabetic symptoms, and chronic back pain and were then excluded for any positive occurrences. All subjects who volunteered to participate in the study met the inclusion criteria with no exclusions being made. Of the original pool of subjects, two subjects (one male and one female) decided to withdraw for personal reasons prior to any data collection. In the original data published by Sobeih and associates [20], there were 13 males and 1 female. For the current analyses, the female was removed from the data set due to the potential for gender-specific influences on obesity and postural stability. The remaining 13 male participants were then classified into two categories: 1) obese (BMI > 30 kg/m2) and 2) overweight/normal (BMI < 30 kg/m2). All participating firefighters were Caucasian and were actively working in the fire station.
Table 1.
Summary of the personal characteristics of the 13 male firefighter participants (mean values with standard deviations in parentheses)
| Obesity Group | Age (years) |
Experience (Years) |
Height (cm) |
Weight (kg) |
Body Mass Index (kg/m2) |
|---|---|---|---|---|---|
| Obese | 32.5 (6.3) |
12.7 (6.4) |
182.2 (8.9) |
115.5 (20.5) |
34.6 (4.4) |
| Overweight/Normal | 32.3 (7.3) |
8.1 (4.8) |
186.9 (8.1) |
88.9 (7.7) |
25.6 (3.5) |
2.2. Measurement of postural balance
A portable microprocessor-based postural balance measurement system was used to continuously monitor the movement of the body’s center of pressure (CP) while performing specific test conditions. The test conditions were designed to evaluate the contributions by various afferents relevant for postural control [2]. During the maintaining of upright postures, the body relies upon three sensory afferents or inputs – visual, somatosensory, and vestibular to control postural sway during standing and other handling tasks. Quantification of the natural variation in movement of CP through a noninvasive method provides an indirect measure of the effect of both physiological and biomechanical stress on the subject [14]. The portable postural balance measurement system contains a force platform system, Accusway Plus (Advanced Mechanical Technologies Inc. Watertown, MA) along with a laptop computer in conjunction with SwayWin95 software. The software quantifies the position of the CP over the entire data collection trial (signal collected at 50 Hz). The output from this system is used to calculate the x and y coordinates (in the horizontal plane) of the movement of the CP [21]. The movement of CP has been used for quantifying postural balance or sway in previous research studies under similar conditions tested in the current study [1,7,12,13,15,18,19].
2.3. Data collection procedure
At the beginning of each data collection day and at the end of each session, a standardized calibration test was conducted on the portable postural balance measurement system to ensure the highest quality of data and repeatability of the signals. For each participant, assessments were conducted at the start of the work shift and at 12-hour intervals until they left work. After being enrolled into the study, participants signed the consent form and completed the health and demographic characteristic questionnaire. During each assessment, the participants completed a session questionnaire and had their postural balance measured while completing three test conditions or tasks (standing stationary with eyes open, standing stationary on foam with eyes closed, and reaching) while wearing the turnout gear with and without the Self Contained Breathing Apparatus (SCBA). In half of the test trials, the firefighters wore turnout gear consisting of standard US firefighter protective apparel (garment, pants, helmet, and boots) weighing about 10 kg. For the other half of the tests, the firefighters wore turnout gear and the SCBA which was a standard US firefighter metal air bottle on their backs with the face-piece around their necks (total weight was about 20 kg). Each of these tests lasted 30 seconds. The current study evaluated the most demanding conditions where the firefighters performed the tasks with turnout gear and turnout gear with SCBA. These conditions were chosen to more effectively evaluate the role of obesity in the responses to conditions similar to the most demanding conditions in fire and rescue response. Complete results of all the conditions can be found in our previously published paper [20]. This protocol was used in previous studies to indirectly assess the effect of different stressors on the central nervous system (CNS) [2].
During each of the actual testing conditions or trials, participants stood in the middle of the force plate with their feet approximately shoulder width apart. Their footprints were traced on the first session and saved for the following tests to standardize the position of their feet. Physical measurement of height and weight were collected for each participant at the time of enrollment (first assessment).
2.4. Study design
The study was a repeated measures design where each firefighter completed the set of tests at 12-hour intervals. The dependent variables included sway area (SA) – the area encompassing the x-y plot of the body’s CP in the horizontal x-y plane due to sway (also known as a stabilogram), sway length (SL) – the total distance traveled by the CP during the test period, medio-lateral (ML) excursion – net deviation of CP in the medial-lateral direction (side to side) and anterio-posterior (AP) excursion – net deviation of CP in the anterior-posterior direction (front to back). The independent variables included obesity group – obese firefighters based on BMI > 30 kg/m2 and overweight/normal firefighters based on BMI < 30 kg/m2 and task – standing with eyes open, standing on foam with eyes closed, and reaching. For the standing with eyes open task, the firefighters remained still for 30 seconds with their arms at the side. For this test, postural balance was control by all three afferents i.e. visual, vestibular and proprioception systems. For the eyes closed standing on foam task, the participants stood on a 4-inch thick foam that was placed on top of the force plate and remained stationary with the arms at the side and with their eyes closed. This particular task required the firefighter to rely primarily upon the vestibular system inputs to remain steady. This task simulates a situation where there is limited visibility (e.g. heavy smoke) and the floor is not stable enough to provide accurate proprioceptive input for postural control (possibly due to fire related destruction and/or slippery conditions). During the reaching task, the participants stood on the platform for eight seconds in an upright and still position and the bent over and lifted a five-pound weight from a shelf placed at knee height directly in front to chest level (upright posture). Once obtaining upright posture, the participant lowered the weight to the shelf and repeated this sequence 3 more times at which time the participant stood quietly for the remaining part of the 30-second test period. This test evaluated the maintenance of postural balance during task performance. Previous studies have indicated that these tasks were sensitive to subtle postural balance responses when the central nervous system is placed in a challenging environment [2,4,18].
2.5. Data and statistical analayses
Customized software computed the postural balance outcome variables (SA, SL, ML excursion, and AP excursion). A repeated measures split-plot analysis of variance (ANOVA) was performed for each of the independent variables utilizing the Statistical Analysis System (SAS) with main effects of task (eyes closed on foam and reach), obesity group (obese and overweight/normal), and work shift duration (session one, two, and three). A full factorial design with interactions was employed with obesity being nested within the subject variable. An alpha-level of 0.05 was used to judge significance for effects with least significant difference (LSD) t-tests being utilized to determine the source of the significance.
3. Results
The statistical analysis (see Table 2 for summary of the ANOVA results) indicated that obesity group and task main effects significantly impacted all four of the postural balance indices (P < 0.02). In addition, the interaction between task and obesity group was significant for postural sway and medio-lateral excursion (p < 0.02). Table 3 provides a summary of the main effects of obesity group and task on the postural balance parameters. As expected, all of the postural balance parameters were largest for the reach task while the standing with eyes open task had the lowest values. All of the postural balance parameters were found to be significantly lower for the obese firefighters as compared to the normal/overweight group (between 4 and 17% difference). These consistent results indicate that the overall postural balance was impacted by both obesity group and task.
Table 2.
Summary (p-values) for the Analysis of Variance tests for each of the independent variables (Bold values represent statistical significance at p < 0.05)
| Sway Area | Sway Length | Medio-Lateral Excursion | Anterior-Posterior Excursion | |
|---|---|---|---|---|
| Obesity Group (OG) | 0.0007 | 0.005 | 0.05 | 0.02 |
| Task (Ta) | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 |
| Time (Ti) | 0.36 | 0.16 | 0.06 | 0.40 |
| OG*Ta | 0.02 | 0.17 | 0.13 | 0.02 |
| OG*Ti | 0.44 | 0.43 | 0.22 | 0.80 |
| Ti*Ta | 0.99 | 0.54 | 0.19 | 0.52 |
| OG*Ta*Ti | 0.79 | 0.70 | 0.82 | 0.57 |
Table 3.
Summary (mean and standard deviation) of postural stability indices (SA, SL, ML excursion, and AP excursion) as a function of obesity group and task (all effects significant at p < 0.02)
| Sway Area (cm2) | Sway Length (cm) | Medio-Lateral Excursion (cm) | Anterior-Posterior Excursion (cm) | |
|---|---|---|---|---|
| Obesity Group | ||||
| Obese | 13.98 (13.80) | 86.31 (52.16) | 3.54 (1.86) | 5.73 (3.93) |
| Normal/Overweight | 16.46 (16.64) | 90.67 (55.38) | 3.69 (1.82) | 6.20 (4.49) |
| Task | ||||
| Standing with Eyes Open | 2.56 (1.36) | 34.29 (9.05) | 1.91 (0.73) | 2.24 (0.76) |
| Standing on Foam with Eyes Closed | 8.37 (4.45) | 75.28 (21.79) | 3.41 (1.16) | 4.26 (1.40) |
| Reaching | 34.84 (9.49) | 156.09 (20.04) | 5.53 (1.28) | 11.42 (2.10) |
While the main effect of both obesity group and task were significant, two interactions were noted as being significant and need to be interpreted to understand these effects. First, for postural sway, there was virtually no difference between the two obesity groups during the standing with eyes open task but significant differences occur when standing on foam with eyes closed and reaching tasks. It is under these conditions that the obese firefighters reduced postural sway by as much as 18% to 26% as compared to the normal/overweight group. Medio-lateral excursion exhibited an almost identical trend as postural sway with obese firefighters having lower medio-lateral excursion under the standing on foam with eyes closed and even lower for the reaching task. Thus, the excursion and sway area was most altered by excessive weight under more extreme conditions, indicating that obese firefighters may adapt differently. This may have significant ramifications on how firefighters respond in diverse and demanding environments.
4. Discussion
While some of the results are very intriguing, there are a few limitations that need to be discussed to truly understand the results. First, the number of subjects was relatively small, which may limit the broader generalization of the results. However, significance was detected for several of the effects of interest, thus limiting the potential impact of a statistical power issue. The small number of subjects may also be subjected to potential bias of the sample recruited. A small sample size also limits the ability to statistically control for potential co-factors that may also help to explain the results. The study population was limited to male firefighters from one fire department. As a result, the postural stability responses may be more reflective of males under a more suburban fire station that has many emergency runs with few structural fires. During the current observation period (random days of testing), the emergency runs that the firefighters responded to were all emergency medical service runs (EMS runs) and no actual fires were encountered. Fire runs would typically be expected to be more physically demanding than EMS runs and may involve exposure to combustion products, some of which may have significant effects on the CNS. Thus, the current results may reflect the current environmental exposures and demands with some limitations to the generalizability of the results.
A second limitation of the sample population was the breakdown of obesity groups which was based on body mass index and does not take into account muscle weight. For example, a very large and muscular firefighter may have a high BMI but be in very good shape physically. Also, several of the normal/overweight firefighters had BMI that were close to the 30 kg/m2 classification level, which may have clouded the results. A larger study with more firefighters in three classification groups (normal, overweight, and obese) may provide better insight into the complex response in firefighters with excessive body weight. Further, morbidly obese firefighters may be at increased risk of postural instability, which was not adequately explored in the current study. The obese group was well below the morbidly obese category with only one firefighter above the morbidly obese limit. Thus, the results of the current study may reflect a relatively “healthy” obese group. The bottom line with these limitations is that the results offer only an initial snap shot of the impact of obesity in firefighters. Furthermore, there remains a need for a larger more comprehensive investigation of the postural balance response under many of the diverse environments that firefighters face on a daily basis as well as to identify whether obese and particularly morbidly obese firefighters respond differently than firefighters with healthy and normal body weight.
Overall, there was a clear indication that the obese firefighters had adjusted their postural stability response to become more conservative with respect to their base of support, thus potentially reducing the risk of falls during tasks that exploit different neuromuscular control systems. However, additional analysis indicated that obese firefighters actually had worse postural balance outcomes during the standing task with eyes open while wearing only the firefighter uniform (no turnout gear or SCBA). Under this basic task, the sway area and sway length were greater (although not significant) for obese firefighters than the normal/overweight firefighters (for SA- obese: 2.4 cm2 vs. normal/overweight: 2.15 cm2, for SL- obese: 37.1 cm vs. normal/overweight: 34.1 cm). When the firefighters were required to perform tasks with unstable floor (e.g. standing on foam) or perform a lifting task (e.g. reaching), the obese firefighters reduced their postural sway. One hypothesized reason for these compensations might be that more control is required of the postural sway due to the center of pressure for obese firefighters being more anterior as compared to the normal/overweight firefighters due to the excessive adipose tissue around the torso (e.g. pot-belly). Having a more anterior center of pressure may place the firefighter closer to the boundaries of their base of support, even though the motion of the posture is smaller. Thus, these compensations may be a safety mechanism that the obese firefighters have adapted over the years.
These reductions in postural sway may also represent a triggered conditional reflex that the firefighters have learned over time. Under the current conditions, the firefighters performed the tasks with turnout gear with and without SCBA, requiring additional muscular response and control during the more demanding tasks (standing on foam with eyes closed and reaching). This muscular response may have produced contractions that reduced the postural sway through more coactivation. An increased muscular contractions required by the obese group suggest that this group is maintaining postural balance at a higher muscular workload than that used by the overweight group. Furthermore, chronic use of higher muscular workload in the obese group would render them to develop fatigue easily when presented with tasks challenging their postural stability. There may be some credence to the learned motor pattern since the obese firefighters were more experienced (on average by 4.5 years) than the normal/overweight firefighters. As a person gains weight, one can adapt to the slow changes in weight distribution as well as alter their neuromuscular response as a protective response. Part of this response would lead to a “healthy worker” population where only the most advantageous obese firefighters can withstand the demands of the job without suffering an injury due to a slip or fall.
Sobeih and associates [20] reported a similar potential of a learned conditional reflex where the gear worn significantly impacted the postural sway of the firefighters. When the firefighters wore either the turnout gear or turnout gear with SCBA, the postural balance parameters were significantly reduced as compared to the regular firefighter uniform. The addition of 10 to 20 kg of weight appears to have resulted in the triggering of a conditional reflex, where firefighters become more alert and recruit more muscles to maintain their balance. It appears that the extra weight for obese firefighters has a very similar response where postural sway measurements were also reduced. Obviously, this effect needs to be further explored along with how experience may alter the conditional reflex response. It is interesting to note that under simple static tasks, Punakallio et al. [16] reported that the use of SCBA increased postural sway parameters among firefighters tested during their off-duty time, which is in contradiction to the current study. Further, other researchers have identified the use of SCBA as a potential risk factor of fire ground injuries due to falls (Heineman et al. [8]). The results of these previous studies indicate that the maintenance of appropriate posture in firefighting situations is very complex with a tremendous need to more comprehensively explore the postural stability responses in firefighters. This can not be done by one simple study but may require a major research focus from multiple researchers.
One final interesting note was about the overall status of the firefighters postural sway as compared to the general population. The general population’s mean postural sway area [Mean age: 33.6 (6.9), N = 35] in standing with eyes open (baseline condition) was 1.78 cm2 (0.96 SD) as compared to the obese firefighters (2.4 cm2) and normal/overweight (2.15 cm2) [17]. This increase in postural sway area indicates that the postural balance of the firefighters may already be compromised. Thus, the conservative approach through the reduction of postural sway by obese firefighters may be a necessity with respect to safety.
5. Conclusion
The results indicate that postural balance was significantly impacted by both obesity and task being performed by the firefighters. Based on the results and the potential influence of experience, there appears to be conditional reflex that reduces the postural sway in the obese group. Obese firefighters reduced their postural sway as compared to normal/overweight firefighters during tasks that tax the neuromuscular system such as standing on unstable floor or reaching for objects. Future research needs to more comprehensively evaluate the role of excessive weight through a larger study that expands the full spectrum of body masses. Finally, the study was the first of its kind to identify the potential shift in postural sway among obese firefighters, shedding light on the neuromuscular adaptations to demanding tasks. However, we are just beginning to understand the ramifications of these adaptations and compensations.
Fig. 1.
Postural sway for obese and Normal/Overweight firefighters during the three tasks: 1) standing with eyes open, 2) standing on foam with eyes closed, and 3) reaching for weight.
Fig. 2.
Medio-lateral excursion for obese and Normal/Overweight firefighters during the three tasks: 1) standing with eyes open, 2) standing on foam with eyes closed, and 3) reaching for weight.
Acknowledgements
This research project was partially funded by a pilot research training grant from the University of Cincinnati’s Education and Research Center (ERC) which is supported by the Training Grant T42/CCT510420 from the Center for Disease Control and Prevention/National Institute for Occupational Safety and Health. The contents are the sole responsibility of the authors and do not necessarily represent the official view of the National Institute for Occupational Safety and Health.
References
- [1].Benda B, Riley P and Krebs D, Biomechanical Relationship Between Center of Gravity and Center of Pressure During Standing, IEEE Transactions on Rehabilitation Engineering 2 (1994), 4–9. [Google Scholar]
- [2].Bhattacharya A, Morgan R, Shukla R, Ramakrishanan HK, and Wang L, Non-invasive estimation of afferent inputs for postural stability under low levels of alcohol, Annals of Biomedical Engineering 15 (1987), 533–550. [DOI] [PubMed] [Google Scholar]
- [3].Byczek L, Walton SM, Conrad KM, Reichelt PA and Samo DG, Cardiovascular Risks in Firefighter – Implications for occupational health nurse practice, AAOHN Journal 52 (2004), 66–76. [PubMed] [Google Scholar]
- [4].Chiou S, Bhattacharya A, Lai CF and Succop P, Effects of Environmental and Task Risk Factors on Workers’ Perceived Sense of Postural Sway and Instability, Occupational Ergonomics 1 (1998), 81–93. [Google Scholar]
- [5].Clark S, Rene A, Theurer W and Marshall M, Association of body mass index and health status in firefighters, Journal of Occupational and Environmental Medicine 44 (2002), 940–946. [DOI] [PubMed] [Google Scholar]
- [6].Corlett E and Manenica I, The effects and measurement of working postures, Applied Ergonomics 11 (1980), 7–16. [DOI] [PubMed] [Google Scholar]
- [7].Dick RB, Bhattacharya A and Shukla R, Use of a computerized postural sway measurement system for neurobehavioral toxicology. Neurotoxicology and Teratology 12 (1990), 1–6. [DOI] [PubMed] [Google Scholar]
- [8].Heineman EF, Shy CM and Checkoway H, Injuries on the fireground: risk factors for traumatic injuries among professional firefighters, American Journal of Industrial Medicine 15 (1989), 267–282. [DOI] [PubMed] [Google Scholar]
- [9].Kales SN, Polyhronopoulos GN, Aldrich JM, Leitao EO and Christiani DC, Correlates of body mass index in hazardous materials firefighters, Journal of Occupational and Environmental Medicine 41 (1999), 589–595. [DOI] [PubMed] [Google Scholar]
- [10].Karter MJ, Patterns of Firefighter Fireground Injuries, 2000.
- [11].Karter MJ and Molis JL, US Firefighter Injuries −2001. 2003.
- [12].Kincl LD, Bhattacharya A, Succop PA and Clark CS, Postural sway measurements: a potential safety monitoring technique for workers wearing personal protective equipment, Applied Occupational and Environmental Hygiene 17 (2002), 256–266. [DOI] [PubMed] [Google Scholar]
- [13].Kuo W, Bhattacharya A, Succop P and Linz D, Postural stability assessment in sewer workers, Journal of Occupational and Environmental Medicine 38 (1996), 27–34. [DOI] [PubMed] [Google Scholar]
- [14].Nashner L, Practical Biomechanics and Physiology of Balance, in: Handbook of Balance Function Testing, Gnckj Jacobson, ed., St. Louis, MO: Mosby Year Book, 1993. [Google Scholar]
- [15].Pippenger C, Effects of a respirator helmet and postural fatigue on upright balance, Department of Environmental Health, University of Cincinnati, 1993. [Google Scholar]
- [16].Punakallio A, Lusa S and Luukkonen R, Protective equipment affects balance abilities differently in younger and older firefighters, Aviation Space and Environmental Medicine 74 (2003), 1151–1156. [PubMed] [Google Scholar]
- [17].Sack DM, Linz D, Shukla R, Rice C, Bhattacharya A and Suskind R, Health Status of Pesticide Applicators: Postural Stability Assessments, Journal of Occupational Medicine 35 (1993), 1196–1202. [PubMed] [Google Scholar]
- [18].Seliga R, Bhattacharya A, Succop P, Wickstrom R, Smith D and Willeke K, Effect of work load and respirator wear on postural stability, heart rate, and perceived exertion, American Industrial Hygiene Association Journal 52 (1991), 417–422. [DOI] [PubMed] [Google Scholar]
- [19].Smith LB, Bhattacharya A, Lemasters G, Succop P, Puhala E, Medvedovic M and Joyce J, Effect of chronic low-level exposure to jet fuel on postural balance of US Air Force personnel, Journal of Occupational and Environmental Medicine 39 (1997), 623–632. [DOI] [PubMed] [Google Scholar]
- [20].Sobeih TM, Davis KG, Succop PA, Jetter WA and Bhattacharya A, Postural balance changes in on-duty firefighters: effect of gear and long work shifts, Journal of Occupational and Environmental Medicine 48 (2006), 68–75. [DOI] [PubMed] [Google Scholar]
- [21].Wickstorm R, Bhattacharya A and Shukla R, Changes in Postural Stability, Performance, Perceived Exertion and Discomfort with Manipulative Activity in a Sustained Stooped Posture, Trends in Ergonomics and Human Factors 5 (1988) 795–800. [Google Scholar]