Applied Ergonomics 48 (2015) 42e48
Contents lists available at ScienceDirect
Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo
Effect of firefighters' personal protective equipment on gait Huiju Park a, *, Seonyoung Kim a, 1, Kristen Morris a, 2, Melissa Moukperian a, 2, Youngjin Moon b, 3, Jeffrey Stull c, 4 a
Department of Fiber Science and Apparel Design, Cornell University, Ithaca, NY, USA Korea Institute of Sports Science, San223-19, Gongneung-dong Nowon-gu, Seoul, South Korea c International Personnel Protection Inc., P. O. Box 92493, Austin, TX 78709-2493, USA b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 January 2014 Accepted 5 November 2014 Available online xxx
The biomechanical experiment with eight male and four female firefighters demonstrates that the effect of adding essential equipment: turnout ensemble, self-contained breathing apparatus, and boots (leather and rubber boots), significantly restricts foot pronation. This finding is supported by a decrease in anterior-posterior and medial-lateral excursion of center of plantar pressure (COP) trajectory during walking. The accumulation of this equipment decreases COP velocity and increases foot-ground contact time and stride time, indicating increased gait instability. An increase in the flexing resistance of the boots is the major contributor to restricted foot pronation and gait instability as evidenced by the greater decrease in excursion of COP in leather boots (greater flexing resistance) than in rubber boots (lower resistance). The leather boots also shows the greatest increase in foot contact time and stride time. These negative impacts can increase musculoskeletal injuries in unfavorable fire ground environments. © 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.
Keywords: Firefighters Foot Gait
1. Introduction Firefighting is one of many physically demanding occupations, where daily tasks often occur in dangerous environments (Coca et al., 2010). Wearing personal protective equipment (PPE) is the only, irreplaceable protection for firefighters who are exposed to multiple hazards. Firefighters' PPE includes turnout coat, pants, boots, hood, gloves, self-contained breathing apparatus and helmet, which are governed by NFPA (National Fire Protection Association) 1971 and 1981 standards. These items of PPE are designed and certified by following NFPA's rigorous requirements and testing
* Corresponding author. 131 Human Ecology Building, Department of Fiber Science and Apparel Design, Cornell University, Ithaca, NY 14853, USA. Tel.: þ1 607 255 0185; fax: þ1 607 255 1093. E-mail addresses: [email protected] (H. Park), [email protected] (S. Kim), [email protected] (K. Morris), [email protected] (M. Moukperian), moonyj@ sports.re.kr (Y. Moon), [email protected] (J. Stull). 1 131 Human Ecology Building, Department of Fiber Science and Apparel Design, Cornell University, Ithaca, NY 14853, USA. Tel.: þ1 607 255 0185; fax: þ1 607 255 1093. 2 T41 Human Ecology Building, Department of Fiber Science and Apparel Design, Cornell University, Ithaca, NY 14853, USA. Tel.: þ1 607 255 3151; fax: þ1 607 255 1093. 3 Tel.: þ82 2 970 9500; fax: þ82 2 970 9502. 4 Tel.: þ1 512 288 8272; fax: þ1 512 344 9588. http://dx.doi.org/10.1016/j.apergo.2014.11.001 0003-6870/© 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.
methods to protect firefighters from not only flame and high heat, but also from exposure to hazardous liquid, physical, and electrical hazards. Boorady et al. (2013) reported that the enhanced protection of PPE has greatly reduced burn injuries. However, recent literature (Chiou et al., 2012; Punakallio, 2005; Sobeih et al., 2006) reported that wearing PPE poses additional adverse effects, such as restricting movement and impeding firefighter job performance. Smith (2008) found that added weight and bulkiness of PPE for enhanced protection led to increased mobility restriction and physical strains. Park et al. (2010) reported that impaired body balance and mobility restriction are the most significant contributors to musculoskeletal injuries such as slips, trips and falls. These injuries accounted for 27.6 percent of firefighters' on-duty injuries in 2003 (Sobeih et al., 2006). NFPA (2014) also reported that the number of US firefighters' fireground injuries in 2012 from sprain and strain (55%) is greater than burn injuries (7%), thermal stress (6%), and toxic gas inhalation (4%). Such fireground injuries account for 25% of the total injury-related time lost for firefighters (Cloutier and Champoux, 2000). Physically demanding environments in conjunction with cumbersome PPE further increase challenges placed on personal balance control systems while working on unfavorable fireground with typically low visibility in damaged building structure (Punakallio, 2005; Sobeih et al., 2006). Hence, firefighters' locomotion and body balance are critical to safety and job performance.
H. Park et al. / Applied Ergonomics 48 (2015) 42e48
A review of the literature identified the negative effect of PPE on firefighters' locomotion and work efficiency. Physiological studies show that heavy and bulky PPE is a dominant factor contributing to fatigue with increased energy expenditure, causing more injuries (Chiou et al., 2012). Punakallio (2005) and Park et al. (2010) concluded that the self-contained breathing apparatus (SCBA) was the single-most influential piece of firefighting gear effecting balance. Park et al. (2010) further demonstrated that the weight of SCBA is closely related to the risk of slipping trauma. Taylor et al. (2011) found that footwear had a greater impact on firefighter exertion than other equipment, such as SCBA and turnout ensembles. Studies that specifically investigated the impact of firefighters' boots on physiological stress and job performance found the weight of firefighter boots to significantly increase physiological stress. Neeves et al. (1989) reported that wearing heavier rubber boots resulted in greater negative impact on firefighters' performance as compared to lighter weight leather boots, because of the greater fatigue associated with energy expenditure while wearing rubber boots. However, the recent study by Huang et al. (2009) found conflicting results. Their study showed that, when wearing rubber boots, firefighters were more effective in resisting fatigue and had increased force production than when wearing leather boots. The study did not find evidence of greater fatigue in rubber boots than in leather boots, although the rubber boots (2.93 ± 0.24 kg) weighed more than leather boots (2.44 ± 0.21 kg). Although the impact of the turnout ensemble, SCBA, and boots on firefighters' performance has been studied, the available data is insufficient to draw a consensus on the level of negative impact of those factors. The current body of literature has not investigated the incremental impact of wearing each item (turnout ensemble, SCBA, and boots) on body balance and gait pattern. Considering the importance of firefighters' locomotion and dynamic body balance on unfavorable fireground, this study aimed to 1) investigate impacts of wearing each item (turnout ensemble, SCBA, and boots) on gait by using plantar pressure sensor technology, and 2) identify contributing factors that affect gait, which may serve as practical implications to improving design of PPE for enhanced gait performance and improved body balance. 2. Research background 2.1. Impeding factors to normal gait and body balance Human gait is achieved through a biphasic forward movement of the center of gravity of the human body, in which stance phase and swing phase movements alternate. Stance phase refers to the time period when the foot is in contact with the ground for foot pronation (heel strikeemid stanceetoe off), bearing the body weight and maintaining body balance. Swing phase indicates the time period when the foot is not in contact with the ground (Gage, 2004). Normal gait consists of approximately 60% stance phase and 40% swing phase with about 20% of the time spent in the double support phase, where the two feet are in contact with the ground at the same time (Perry, 1992). Literature indicates additional weight and footwear characteristics as external factors affecting body balance and gait pattern. Additional weight on the body amplifies dynamic instability, pulling the new center of mass (body mass þ added weight) away from the original point, located inside the pelvis, without load carriage (Gronqvist et al., 1989; You et al., 2001; Regia-Corte and Wagman, 2008; Park et al., 2013). Therefore, the center of gravity of the total system, which is a vertical projection of the center of mass of the system on the ground, moves away from the base of support (Gronqvist et al., 1989; You et al., 2001). This has been found to
43
increase dynamic instability, causing greater risk of traumatic injuries such as falling and slipping (You et al., 2001). Therefore, the human body automatically alters the gait pattern in order to maintain balance by increasing the stance phase and double support time (Birrell and Haslam, 2010; Kinoshita, 1985; Park et al., 2013). The characteristics of footwear such as fit, footwear morphology, and flexing resistance constitute another external factor. For example, looseness of the footwear makes the foot slide forward and causes the foot to be squeezed in the toe area, which lead to joint and tissue deformation. This results in impaired foot function and altered gait (Goonetilleke, 2012). In addition, wearing footwear with a high outsole (e.g. high-heeled shoes) changes range of motion of the foot by limiting foot abduction, eversion and medial rotation (Goonetilleke, 2012). An increase in heel height also induces excessive weight bearing on the forefoot. These two factors resulting from the height of the outsole leads to a significant change in gait pattern and also leads to disturbed body balance, and increased risk of ankle sprain and rapid fatigue (Goonetilleke, 2012). Similarly, wearing footwear with high flex resistance due to stiff materials or poor construction can cause mechanical binding and poor interaction between foot, footwear, and the ground that can impair foot function and alter gait (Cikajlo and Matja ci c, 2007). 2.2. Analysis of plantar pressure distribution Gait analysis has been done in several ways using biomechanical measurement technologies such as three-dimensional motion analysis systems and force plates. In addition, analysis of the dynamic change in plantar pressure distribution is widely used to diagnose gait changes and balance control problems (Abdul Razak et al., 2012). By calculating the timing and duration of the plantar pressure detected on a specific part of the foot, current technology is capable of assessing changes in stance phase, swing phase, double support, stride time, walking velocity and other spatiotemporal parameters of gait. Specifically, the center of plantar pressure (COP) has been used as an indicator of changes in gait and body balance related to fall injury risks in biomechanics (Maki et al., 1994; Stel et al., 2003). COP is the point where all ground reaction forces, acting on the foot when it is in contact with the ground, are balanced (Harris and Smith, 2007). COP is considered to be concentrated and representative of the total force by the foot required to move the body forward while maintaining balance during walking. It is a calculated value based on the amplitude of plantar pressure and the location of the individual pressures under the plantar foot (Harris and Smith, 2007). In normal walking, COP travels from the middle of the heel, passing through the midpoint towards the big toe, creating a bow shaped trajectory as shown in Fig. 1 (Harris and Smith, 2007). Restricted foot movement resulting from external stimuli such as poorly designed footwear, decreases the anteriorposterior (AP) and the medial-lateral (ML) excursion of COP trajectory (Fig. 1). 3. Methodology To identify changes in gait in different PPE configurations, a series of human performance tests were conducted. With institutional review board approval, eight male firefighters (age: 28.6 ± 8.3, height: 183.5 ± 3.8 cm, weight: 85.5 ± 15.7 kg) and four female firefighters (age: 31.5 ± 13.5, height: 170.8 ± 7.6 cm, weight: 68.3 ± 14.3 kg) were recruited from the North Eastern region of the U.S. All participants were structural firefighters with an average of 6.58 years of experience and had no history of any orthopedic or muscular disorders or surgery or deformities. Only right-handed
44
H. Park et al. / Applied Ergonomics 48 (2015) 42e48
Fig. 1. COP trajectory during stance phase.
volunteers were recruited to control for possible influence of dominance on movement patterns. Three of the participants were career firefighters, while the remaining nine participants were volunteer firefighters. 3.1. PPE configurations and boot fitting Five different garment conditions were tested (Fig. 2). Garment condition G1 includes each participant's own short sleeve T-shirt with shorts, running socks and previously broken-in running shoes that they have worn in order to allow for the participants' natural body movements. Garment condition G2 includes wearing the participant's own turnout coat and pants, on top of G1, without gloves and tools. Garment condition G3 includes additionally wearing SCBA, without gas in the air bottle and face mask. Garment conditions G1 through G3 were designed to identify the incremental impact of wearing turnout gear (G2) and SCBA (G3) while wearing the running shoes. Conditions G3 through G5 were designed to identify the impact of footwear design while wearing turnout gear and SCBA. Garment conditions G4 and G5 included the
same garment configuration as G3, but also firefighting rubber boots (G4) or leather boots (G5) instead of the running shoes. All participants wore the same styles of rubber and leather boots, which were certified to the 2007 edition of NFPA 1971, Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting. To ensure the proper boot size, multiple sizes of new rubber and leather boots were offered to each participant 1e2 weeks before the experiment. In the standardized fitting process, participants were asked to don their entire PPE including the SCBA and helmet with the prospective boots. While wearing the socks normally worn with the PPE ensemble, they walked for 3 min to determine adequate comfort and fit. The process was repeated if necessary with different sizes of boots until the proper size was identified. The method was repeated for both the rubber and leather styles. This process was performed to control for possible impact of poor footwear size on foot movement and gait pattern. Each participant was instructed to wear both new pairs of rubber and leather boots for a minimum of 3 h before the experiment in order to familiarize participants with the given boots. This process was done to minimize the possible impact of wearing new footwear on gait pattern in the experiment. The researchers recorded the characteristics of each PPE item used in G1through G5 as summarized in Table 1. Considering the research purpose of identifying changes in gait pattern, the researchers measured the longitudinal flex resistance of the footwear based on ISO 17707, FootweareTest methods for outsoleseFlex resistance, as shown in Fig. 3. The footwear (running shoes, rubber boots, and leather boots) was placed on top of two folding plates with the creasing point of the footwear located at the hinge (folding point) of the two plates. The forefoot section of the footwear was firmly fixed and weight was added until the rear section of the footwear flexed to 30 from the base (Fig. 3). The applied weight for the 30 longitudinal flex was then converted to a force unit. The running shoes had the least resistance, the rubber boots had the next highest level of resistance, and the leather boots showed the highest resistance as shown in Table 1. 3.2. Walking trials In each garment condition, an in-shoe plantar pressure sensor (F-scan Inc., Boston, MA) was placed on the insole of both the left
Fig. 2. Garment conditions G1 ~ G5. Adapted with permission from “Beyond Protection: Technology and Design Moving toward Human Factors of Fire Gear”, by Park et al., 2014, AATCC Review.
H. Park et al. / Applied Ergonomics 48 (2015) 42e48
and right test shoes to measure plantar pressure distribution for the calculation of the center of plantar pressure (COP) trajectory and measurement of gait pattern. After donning PPE items and test shoes, the participant was instructed to walk, starting with their left foot, 10 m in a straight line on a level wooden floor at a selfpreferred speed. The task was repeated three times for each of the five garment conditions. The four sequential steps from the third to the sixth step (2 steps of the right foot and 2 of the left foot) were included in the analysis to capture normal walking pattern. This process excluded the initial and terminal steps as they do not represent normal walking patterns. AP excursion of COP (cm), ML excursion of COP (cm), and COP velocity (cm/sec.) in each step during the walking trials were measured at 30 Hz to assess changes in foot function. In order to identify changes in AP/ML excursion of COP in different PPE configurations without the undesirable confounding influence of individual foot size, the two variables were normalized, thus expressed as a percentage of each participant's foot length, instead of actual length. Stride time (sec.), stance phase (%) and double support (%) were analyzed to assess changes in gait pattern. To control for the possible effect of garment order on foot function and gait pattern, each participant was randomly assigned to a balanced-block design of garment conditions. 3.3. Statistical analysis A mixed models analysis was performed using SPSS (version 20). The experimental design was repeated measures because each firefighter was measured repeatedly with five different garment configurations for three walking trials for two steps on each side (left and right side). Responses of the mixed model are normalized anterior-posterior excursion of COP, normalized medial-lateral excursion of COP, COP velocity, stride time (sec.), stance phase (%) and double support (%). Fixed independent variables of interest are gender, garment and their interaction. The models also control for side, step order and order of garment configurations as fixed effect. Participants, garment configurations nested in participants, and
45
Fig. 3. Flexing test.
walking trial nested within garments and participants, are random effects in the model. Post-hoc pairwise comparisons using Bonferroni correction were conducted when the garment effect or its interaction with gender was significant. All statistical tests were done at the 0.05 level of significance. 4. Results The results of the statistical analysis are summarized in Table 2. No significant effect of the order of garment testing conditions was found on any dependent variables. 4.1. Changes in COP trajectory pattern 4.1.1. Normalized AP excursion A significant garment effect was found (p < 0.001) as shown in Table 2. Estimated means of normalized AP excursion in Table 2
Table 1 Garment conditions. Garment conditions
Total weight Clothing & Equipment
Footwear
G1
G2
G3
G4
G5
1.39 (±0.26) kg T-shirts Shorts Socks Running shoes
7.81 (±1.06) kg G1 Turnout ensemble
15.23 (±1.06) kg G2 SCBA
17.67 (±1.35) kg G2 SCBA
17.54 (±1.25) kg G2 SCBA
Running shoes
Running shoes
Rubber boots
Leather boots
Characteristics of items T-shirts, shorts and socks Turnout ensemble SCBA Running shoes (used in G1~G3) Rubber boots (used in G4)
Leather boots (used in G5)
Weight: 0.68 (±0.27) kg Weight: 5.74 (±0.79) kg Weight: 8.1 kg (all participants used the same SCBA) Length: 46 cm, Radius of air bottle: 9.08 cm Weight: 0.71 (±0.24) kg Flex resistance: 5.97 (±2.28) N Weight: 3.15 (±0.29) kg Flex resistance: 27.2 (±1.2) N Collar height: 38 cm from the footbed Outsole height: 3 cm at the heel/1.5 cm at the forefoot Materials: Rubber was used in the upper and outsole. Metal toe cap and metal shank were inserted. Weight: 3.02 (±0.19) kg Flex resistance: 34.4 (±2.6) N Collar height: 34 cm from the footbed Outsole height: 3.5 cm at the heel/1.8 cm at the forefoot Materials: Leather on the lower foot 60% Kevlar/40% Nomex fabric for the upper Rubber was used in outsole Metal toe cap and metal shank were inserted.
46
H. Park et al. / Applied Ergonomics 48 (2015) 42e48
Table 2 Estimated marginal means of garment and gender effect for dependent variables and their statistical significance. Garment effect Items Footwear
Normalized AP excursion (%) Normalized ML excursion (%) COP velocity (cm/sec.) Stride time (sec.) Stance phase (%) Double support (%)
Garment Conditions G1 G2 G3 G4 G5 Short sleeve T-shirts + shorts G1 + Protective ensemble G2 + SCBA G2 + SCBA G2 + SCBA Running Shoes Running Shoes Running Shoes Rubber Boots Leather Boots Flexing resistance Flexing resistance Flexing resistance Flexing resistance Flexing resistance (5.97 ± 2.28N) (5.97 ± 2.28N) (5.97 ± 2.28N) (27.2 ± 1.2N) (34.4 ± 2.6N) Est. Mean
Est. Mean
Est. Mean
Est. Mean
Est. Mean
68.66c
67.67c
67.24bc
64.27ab
63.35a
1.26
10.01
Contents lists available at ScienceDirect
Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo
Effect of firefighters' personal protective equipment on gait Huiju Park a, *, Seonyoung Kim a, 1, Kristen Morris a, 2, Melissa Moukperian a, 2, Youngjin Moon b, 3, Jeffrey Stull c, 4 a
Department of Fiber Science and Apparel Design, Cornell University, Ithaca, NY, USA Korea Institute of Sports Science, San223-19, Gongneung-dong Nowon-gu, Seoul, South Korea c International Personnel Protection Inc., P. O. Box 92493, Austin, TX 78709-2493, USA b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 January 2014 Accepted 5 November 2014 Available online xxx
The biomechanical experiment with eight male and four female firefighters demonstrates that the effect of adding essential equipment: turnout ensemble, self-contained breathing apparatus, and boots (leather and rubber boots), significantly restricts foot pronation. This finding is supported by a decrease in anterior-posterior and medial-lateral excursion of center of plantar pressure (COP) trajectory during walking. The accumulation of this equipment decreases COP velocity and increases foot-ground contact time and stride time, indicating increased gait instability. An increase in the flexing resistance of the boots is the major contributor to restricted foot pronation and gait instability as evidenced by the greater decrease in excursion of COP in leather boots (greater flexing resistance) than in rubber boots (lower resistance). The leather boots also shows the greatest increase in foot contact time and stride time. These negative impacts can increase musculoskeletal injuries in unfavorable fire ground environments. © 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.
Keywords: Firefighters Foot Gait
1. Introduction Firefighting is one of many physically demanding occupations, where daily tasks often occur in dangerous environments (Coca et al., 2010). Wearing personal protective equipment (PPE) is the only, irreplaceable protection for firefighters who are exposed to multiple hazards. Firefighters' PPE includes turnout coat, pants, boots, hood, gloves, self-contained breathing apparatus and helmet, which are governed by NFPA (National Fire Protection Association) 1971 and 1981 standards. These items of PPE are designed and certified by following NFPA's rigorous requirements and testing
* Corresponding author. 131 Human Ecology Building, Department of Fiber Science and Apparel Design, Cornell University, Ithaca, NY 14853, USA. Tel.: þ1 607 255 0185; fax: þ1 607 255 1093. E-mail addresses: [email protected] (H. Park), [email protected] (S. Kim), [email protected] (K. Morris), [email protected] (M. Moukperian), moonyj@ sports.re.kr (Y. Moon), [email protected] (J. Stull). 1 131 Human Ecology Building, Department of Fiber Science and Apparel Design, Cornell University, Ithaca, NY 14853, USA. Tel.: þ1 607 255 0185; fax: þ1 607 255 1093. 2 T41 Human Ecology Building, Department of Fiber Science and Apparel Design, Cornell University, Ithaca, NY 14853, USA. Tel.: þ1 607 255 3151; fax: þ1 607 255 1093. 3 Tel.: þ82 2 970 9500; fax: þ82 2 970 9502. 4 Tel.: þ1 512 288 8272; fax: þ1 512 344 9588. http://dx.doi.org/10.1016/j.apergo.2014.11.001 0003-6870/© 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.
methods to protect firefighters from not only flame and high heat, but also from exposure to hazardous liquid, physical, and electrical hazards. Boorady et al. (2013) reported that the enhanced protection of PPE has greatly reduced burn injuries. However, recent literature (Chiou et al., 2012; Punakallio, 2005; Sobeih et al., 2006) reported that wearing PPE poses additional adverse effects, such as restricting movement and impeding firefighter job performance. Smith (2008) found that added weight and bulkiness of PPE for enhanced protection led to increased mobility restriction and physical strains. Park et al. (2010) reported that impaired body balance and mobility restriction are the most significant contributors to musculoskeletal injuries such as slips, trips and falls. These injuries accounted for 27.6 percent of firefighters' on-duty injuries in 2003 (Sobeih et al., 2006). NFPA (2014) also reported that the number of US firefighters' fireground injuries in 2012 from sprain and strain (55%) is greater than burn injuries (7%), thermal stress (6%), and toxic gas inhalation (4%). Such fireground injuries account for 25% of the total injury-related time lost for firefighters (Cloutier and Champoux, 2000). Physically demanding environments in conjunction with cumbersome PPE further increase challenges placed on personal balance control systems while working on unfavorable fireground with typically low visibility in damaged building structure (Punakallio, 2005; Sobeih et al., 2006). Hence, firefighters' locomotion and body balance are critical to safety and job performance.
H. Park et al. / Applied Ergonomics 48 (2015) 42e48
A review of the literature identified the negative effect of PPE on firefighters' locomotion and work efficiency. Physiological studies show that heavy and bulky PPE is a dominant factor contributing to fatigue with increased energy expenditure, causing more injuries (Chiou et al., 2012). Punakallio (2005) and Park et al. (2010) concluded that the self-contained breathing apparatus (SCBA) was the single-most influential piece of firefighting gear effecting balance. Park et al. (2010) further demonstrated that the weight of SCBA is closely related to the risk of slipping trauma. Taylor et al. (2011) found that footwear had a greater impact on firefighter exertion than other equipment, such as SCBA and turnout ensembles. Studies that specifically investigated the impact of firefighters' boots on physiological stress and job performance found the weight of firefighter boots to significantly increase physiological stress. Neeves et al. (1989) reported that wearing heavier rubber boots resulted in greater negative impact on firefighters' performance as compared to lighter weight leather boots, because of the greater fatigue associated with energy expenditure while wearing rubber boots. However, the recent study by Huang et al. (2009) found conflicting results. Their study showed that, when wearing rubber boots, firefighters were more effective in resisting fatigue and had increased force production than when wearing leather boots. The study did not find evidence of greater fatigue in rubber boots than in leather boots, although the rubber boots (2.93 ± 0.24 kg) weighed more than leather boots (2.44 ± 0.21 kg). Although the impact of the turnout ensemble, SCBA, and boots on firefighters' performance has been studied, the available data is insufficient to draw a consensus on the level of negative impact of those factors. The current body of literature has not investigated the incremental impact of wearing each item (turnout ensemble, SCBA, and boots) on body balance and gait pattern. Considering the importance of firefighters' locomotion and dynamic body balance on unfavorable fireground, this study aimed to 1) investigate impacts of wearing each item (turnout ensemble, SCBA, and boots) on gait by using plantar pressure sensor technology, and 2) identify contributing factors that affect gait, which may serve as practical implications to improving design of PPE for enhanced gait performance and improved body balance. 2. Research background 2.1. Impeding factors to normal gait and body balance Human gait is achieved through a biphasic forward movement of the center of gravity of the human body, in which stance phase and swing phase movements alternate. Stance phase refers to the time period when the foot is in contact with the ground for foot pronation (heel strikeemid stanceetoe off), bearing the body weight and maintaining body balance. Swing phase indicates the time period when the foot is not in contact with the ground (Gage, 2004). Normal gait consists of approximately 60% stance phase and 40% swing phase with about 20% of the time spent in the double support phase, where the two feet are in contact with the ground at the same time (Perry, 1992). Literature indicates additional weight and footwear characteristics as external factors affecting body balance and gait pattern. Additional weight on the body amplifies dynamic instability, pulling the new center of mass (body mass þ added weight) away from the original point, located inside the pelvis, without load carriage (Gronqvist et al., 1989; You et al., 2001; Regia-Corte and Wagman, 2008; Park et al., 2013). Therefore, the center of gravity of the total system, which is a vertical projection of the center of mass of the system on the ground, moves away from the base of support (Gronqvist et al., 1989; You et al., 2001). This has been found to
43
increase dynamic instability, causing greater risk of traumatic injuries such as falling and slipping (You et al., 2001). Therefore, the human body automatically alters the gait pattern in order to maintain balance by increasing the stance phase and double support time (Birrell and Haslam, 2010; Kinoshita, 1985; Park et al., 2013). The characteristics of footwear such as fit, footwear morphology, and flexing resistance constitute another external factor. For example, looseness of the footwear makes the foot slide forward and causes the foot to be squeezed in the toe area, which lead to joint and tissue deformation. This results in impaired foot function and altered gait (Goonetilleke, 2012). In addition, wearing footwear with a high outsole (e.g. high-heeled shoes) changes range of motion of the foot by limiting foot abduction, eversion and medial rotation (Goonetilleke, 2012). An increase in heel height also induces excessive weight bearing on the forefoot. These two factors resulting from the height of the outsole leads to a significant change in gait pattern and also leads to disturbed body balance, and increased risk of ankle sprain and rapid fatigue (Goonetilleke, 2012). Similarly, wearing footwear with high flex resistance due to stiff materials or poor construction can cause mechanical binding and poor interaction between foot, footwear, and the ground that can impair foot function and alter gait (Cikajlo and Matja ci c, 2007). 2.2. Analysis of plantar pressure distribution Gait analysis has been done in several ways using biomechanical measurement technologies such as three-dimensional motion analysis systems and force plates. In addition, analysis of the dynamic change in plantar pressure distribution is widely used to diagnose gait changes and balance control problems (Abdul Razak et al., 2012). By calculating the timing and duration of the plantar pressure detected on a specific part of the foot, current technology is capable of assessing changes in stance phase, swing phase, double support, stride time, walking velocity and other spatiotemporal parameters of gait. Specifically, the center of plantar pressure (COP) has been used as an indicator of changes in gait and body balance related to fall injury risks in biomechanics (Maki et al., 1994; Stel et al., 2003). COP is the point where all ground reaction forces, acting on the foot when it is in contact with the ground, are balanced (Harris and Smith, 2007). COP is considered to be concentrated and representative of the total force by the foot required to move the body forward while maintaining balance during walking. It is a calculated value based on the amplitude of plantar pressure and the location of the individual pressures under the plantar foot (Harris and Smith, 2007). In normal walking, COP travels from the middle of the heel, passing through the midpoint towards the big toe, creating a bow shaped trajectory as shown in Fig. 1 (Harris and Smith, 2007). Restricted foot movement resulting from external stimuli such as poorly designed footwear, decreases the anteriorposterior (AP) and the medial-lateral (ML) excursion of COP trajectory (Fig. 1). 3. Methodology To identify changes in gait in different PPE configurations, a series of human performance tests were conducted. With institutional review board approval, eight male firefighters (age: 28.6 ± 8.3, height: 183.5 ± 3.8 cm, weight: 85.5 ± 15.7 kg) and four female firefighters (age: 31.5 ± 13.5, height: 170.8 ± 7.6 cm, weight: 68.3 ± 14.3 kg) were recruited from the North Eastern region of the U.S. All participants were structural firefighters with an average of 6.58 years of experience and had no history of any orthopedic or muscular disorders or surgery or deformities. Only right-handed
44
H. Park et al. / Applied Ergonomics 48 (2015) 42e48
Fig. 1. COP trajectory during stance phase.
volunteers were recruited to control for possible influence of dominance on movement patterns. Three of the participants were career firefighters, while the remaining nine participants were volunteer firefighters. 3.1. PPE configurations and boot fitting Five different garment conditions were tested (Fig. 2). Garment condition G1 includes each participant's own short sleeve T-shirt with shorts, running socks and previously broken-in running shoes that they have worn in order to allow for the participants' natural body movements. Garment condition G2 includes wearing the participant's own turnout coat and pants, on top of G1, without gloves and tools. Garment condition G3 includes additionally wearing SCBA, without gas in the air bottle and face mask. Garment conditions G1 through G3 were designed to identify the incremental impact of wearing turnout gear (G2) and SCBA (G3) while wearing the running shoes. Conditions G3 through G5 were designed to identify the impact of footwear design while wearing turnout gear and SCBA. Garment conditions G4 and G5 included the
same garment configuration as G3, but also firefighting rubber boots (G4) or leather boots (G5) instead of the running shoes. All participants wore the same styles of rubber and leather boots, which were certified to the 2007 edition of NFPA 1971, Standard on Protective Ensembles for Structural Fire Fighting and Proximity Fire Fighting. To ensure the proper boot size, multiple sizes of new rubber and leather boots were offered to each participant 1e2 weeks before the experiment. In the standardized fitting process, participants were asked to don their entire PPE including the SCBA and helmet with the prospective boots. While wearing the socks normally worn with the PPE ensemble, they walked for 3 min to determine adequate comfort and fit. The process was repeated if necessary with different sizes of boots until the proper size was identified. The method was repeated for both the rubber and leather styles. This process was performed to control for possible impact of poor footwear size on foot movement and gait pattern. Each participant was instructed to wear both new pairs of rubber and leather boots for a minimum of 3 h before the experiment in order to familiarize participants with the given boots. This process was done to minimize the possible impact of wearing new footwear on gait pattern in the experiment. The researchers recorded the characteristics of each PPE item used in G1through G5 as summarized in Table 1. Considering the research purpose of identifying changes in gait pattern, the researchers measured the longitudinal flex resistance of the footwear based on ISO 17707, FootweareTest methods for outsoleseFlex resistance, as shown in Fig. 3. The footwear (running shoes, rubber boots, and leather boots) was placed on top of two folding plates with the creasing point of the footwear located at the hinge (folding point) of the two plates. The forefoot section of the footwear was firmly fixed and weight was added until the rear section of the footwear flexed to 30 from the base (Fig. 3). The applied weight for the 30 longitudinal flex was then converted to a force unit. The running shoes had the least resistance, the rubber boots had the next highest level of resistance, and the leather boots showed the highest resistance as shown in Table 1. 3.2. Walking trials In each garment condition, an in-shoe plantar pressure sensor (F-scan Inc., Boston, MA) was placed on the insole of both the left
Fig. 2. Garment conditions G1 ~ G5. Adapted with permission from “Beyond Protection: Technology and Design Moving toward Human Factors of Fire Gear”, by Park et al., 2014, AATCC Review.
H. Park et al. / Applied Ergonomics 48 (2015) 42e48
and right test shoes to measure plantar pressure distribution for the calculation of the center of plantar pressure (COP) trajectory and measurement of gait pattern. After donning PPE items and test shoes, the participant was instructed to walk, starting with their left foot, 10 m in a straight line on a level wooden floor at a selfpreferred speed. The task was repeated three times for each of the five garment conditions. The four sequential steps from the third to the sixth step (2 steps of the right foot and 2 of the left foot) were included in the analysis to capture normal walking pattern. This process excluded the initial and terminal steps as they do not represent normal walking patterns. AP excursion of COP (cm), ML excursion of COP (cm), and COP velocity (cm/sec.) in each step during the walking trials were measured at 30 Hz to assess changes in foot function. In order to identify changes in AP/ML excursion of COP in different PPE configurations without the undesirable confounding influence of individual foot size, the two variables were normalized, thus expressed as a percentage of each participant's foot length, instead of actual length. Stride time (sec.), stance phase (%) and double support (%) were analyzed to assess changes in gait pattern. To control for the possible effect of garment order on foot function and gait pattern, each participant was randomly assigned to a balanced-block design of garment conditions. 3.3. Statistical analysis A mixed models analysis was performed using SPSS (version 20). The experimental design was repeated measures because each firefighter was measured repeatedly with five different garment configurations for three walking trials for two steps on each side (left and right side). Responses of the mixed model are normalized anterior-posterior excursion of COP, normalized medial-lateral excursion of COP, COP velocity, stride time (sec.), stance phase (%) and double support (%). Fixed independent variables of interest are gender, garment and their interaction. The models also control for side, step order and order of garment configurations as fixed effect. Participants, garment configurations nested in participants, and
45
Fig. 3. Flexing test.
walking trial nested within garments and participants, are random effects in the model. Post-hoc pairwise comparisons using Bonferroni correction were conducted when the garment effect or its interaction with gender was significant. All statistical tests were done at the 0.05 level of significance. 4. Results The results of the statistical analysis are summarized in Table 2. No significant effect of the order of garment testing conditions was found on any dependent variables. 4.1. Changes in COP trajectory pattern 4.1.1. Normalized AP excursion A significant garment effect was found (p < 0.001) as shown in Table 2. Estimated means of normalized AP excursion in Table 2
Table 1 Garment conditions. Garment conditions
Total weight Clothing & Equipment
Footwear
G1
G2
G3
G4
G5
1.39 (±0.26) kg T-shirts Shorts Socks Running shoes
7.81 (±1.06) kg G1 Turnout ensemble
15.23 (±1.06) kg G2 SCBA
17.67 (±1.35) kg G2 SCBA
17.54 (±1.25) kg G2 SCBA
Running shoes
Running shoes
Rubber boots
Leather boots
Characteristics of items T-shirts, shorts and socks Turnout ensemble SCBA Running shoes (used in G1~G3) Rubber boots (used in G4)
Leather boots (used in G5)
Weight: 0.68 (±0.27) kg Weight: 5.74 (±0.79) kg Weight: 8.1 kg (all participants used the same SCBA) Length: 46 cm, Radius of air bottle: 9.08 cm Weight: 0.71 (±0.24) kg Flex resistance: 5.97 (±2.28) N Weight: 3.15 (±0.29) kg Flex resistance: 27.2 (±1.2) N Collar height: 38 cm from the footbed Outsole height: 3 cm at the heel/1.5 cm at the forefoot Materials: Rubber was used in the upper and outsole. Metal toe cap and metal shank were inserted. Weight: 3.02 (±0.19) kg Flex resistance: 34.4 (±2.6) N Collar height: 34 cm from the footbed Outsole height: 3.5 cm at the heel/1.8 cm at the forefoot Materials: Leather on the lower foot 60% Kevlar/40% Nomex fabric for the upper Rubber was used in outsole Metal toe cap and metal shank were inserted.
46
H. Park et al. / Applied Ergonomics 48 (2015) 42e48
Table 2 Estimated marginal means of garment and gender effect for dependent variables and their statistical significance. Garment effect Items Footwear
Normalized AP excursion (%) Normalized ML excursion (%) COP velocity (cm/sec.) Stride time (sec.) Stance phase (%) Double support (%)
Garment Conditions G1 G2 G3 G4 G5 Short sleeve T-shirts + shorts G1 + Protective ensemble G2 + SCBA G2 + SCBA G2 + SCBA Running Shoes Running Shoes Running Shoes Rubber Boots Leather Boots Flexing resistance Flexing resistance Flexing resistance Flexing resistance Flexing resistance (5.97 ± 2.28N) (5.97 ± 2.28N) (5.97 ± 2.28N) (27.2 ± 1.2N) (34.4 ± 2.6N) Est. Mean
Est. Mean
Est. Mean
Est. Mean
Est. Mean
68.66c
67.67c
67.24bc
64.27ab
63.35a
1.26
10.01
