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Effects of Wrist Cooling on Recovery From Exercise-Induced Heat Stress With Firefighting Personal Protective Equipment


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Objective: To determine the effects of wrist cooling on recovery from exercise-induced heat stress (EIHS) from wearing firefighting personal protective equipment (PPE) and self-contained breathing apparatus. Methods: Using a single-blind, counterbalanced, crossover-design, in 11 healthy males, we measured heart rate (HR), HR variability (HRV), core temperature (TCore), thermal strain (TS) and fatigue at rest, during 30-min of exercise in PPE+SCBA, and during recovery while wearing a wrist cooling band (control[off] vs. cool[on]). Results: No differences were observed between trials at baseline or during exercise, in HR, TCore, TS, or fatigue. Time to 50% and recovery were not different between trials. Upon recovery, TCore was lower, while HR, fatigue, HRV, and TS were relatively indifferent with cooling. Conclusion: Wrist cooling after EIHS only modestly enhanced recovery, questioning its implementation during on-scene rehabilitation of firefighters.
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Copyright © 2018 American College of Occupational and Environmental Medicine. Unauthorized reproduction of this article is prohibited
Journal of Occupational and Environmental Medicine, Publish Ahead of Print
DOI : 10.1097/JOM.0000000000001436
Effects of Wrist Cooling on Recovery from Exercise-Induced Heat Stress with
Firefighting Personal Protective Equipment
Emily Schlicht B.S., Ronald Caruso B.S., Kelsey Denby B.S., Alexs Matias B.S., Monique
Dudar, Stephen J. Ives Ph.D.
Department of Health and Human Physiological Sciences, Skidmore College, Saratoga Springs,
Email addresses of coauthors:,,,,,
Corresponding Author:
Stephen J. Ives, Ph.D.
Associate Chair and Assistant Professor
Health and Human Physiological Sciences
Skidmore College
815 N. Broadway
Saratoga Springs, NY 12866
518-580-8366 (phone)
518-580-8356 (fax)
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Conflicts of Interest: None declared
Sources of Support: DhamaUSA provided funding and equipment (to SJI); though the sponsors
had no role in the design of the study; collection, analyses, or interpretation of data; in the
writing of the manuscript, and in the decision to publish the results.
Copyright © 2018 American College of Occupational and Environmental Medicine. Unauthorized reproduction of this article is prohibited
Objective: To determine the effects of wrist cooling on recovery from exercise-induced heat
stress (EIHS) from wearing firefighting personal protective equipment (PPE) and self-contained
breathing apparatus. Methods: Using a single-blind, counterbalanced, crossover-design, in 11
healthy males, we measured heart rate (HR), HR variability (HRV), core temperature (TCore),
thermal strain (TS) and fatigue at rest, during 30-min of exercise in PPE+SCBA, and during
recovery while wearing a wrist cooling band (control[off] vs. cool[on]). Results: No differences
were observed between trials at baseline or during exercise, in HR, TCore, TS, or fatigue. Time to
50% and recovery were not different between trials. Upon recovery, TCore was lower, while HR,
fatigue, HRV, and TS were relatively indifferent with cooling. Conclusion: Wrist cooling after
EIHS only modestly enhanced recovery, questioning its implementation during on-scene
rehabilitation of firefighters.
Keywords: Heart rate recovery, active cooling, fatigue, thermal strain, heart rate variability
Copyright © 2018 American College of Occupational and Environmental Medicine. Unauthorized reproduction of this article is prohibited
Firefighting is an incredibly dangerous occupation that leads to a variety of physiological
stresses [1-3] and can result in loss of life [4-6]. While trauma and burns are expectedly
causative in firefighter mortality [4], cardiovascular-related death is also highly prevalent [4-6].
Specifically, extreme heat, dehydration, and physical exertion-induced metabolic heat
production, coupled with impaired heat dissipation associated with the use of personal protective
equipment (PPE), act in concert to dramatically increase cardiovascular demand [1, 3, 7-9],
which may contribute to the elevated cardiovascular-related death in firefighters [4-6].
Additionally, the general nature of the occupation requires irregular bouts of activity and shift
work [2, 10], which further threatens those with an already heightened risk of heart disease [11,
12]. This cardiovascular strain associated with firefighting and thermoregulation, combined with
underlying cardiovascular disease risk [12] or presence [11], are likely contributing to the fact
that ~50% of on-duty deaths are cardiac related [6], highlighting the need for effective
Currently, firefighters manage heat stress through on-scene rehabilitation, which is
recommended and common practice as per the National Fire Protection Association (NFPA) [13,
14]. On-scene rehabilitation offers firefighters time to rest, recover, cool down, and rehydrate, as
well as time for their vital signs to be monitored [13, 14]. However, previous work suggests that
in the line of duty firefighters often experience relatively rapid increases in core temperature of
>1.9 °C, which are slow to return to baseline, compounding core temperature during subsequent
bouts [1]. Such heat exposure reduces time to fatigue during subsequent bouts (1 hr later), and
likely even the following day [15]. Thus, the ability to recover core temperature from bouts of
firefighting is critical for readiness in subsequent bouts during the same call, but also mission
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readiness for future calls in the same shift. Moreover, this sustained cardiovascular strain
associated with thermoregulation may be contributory to increased incidence of acute
cardiovascular events after firefighting [6]. Collectively, enhancing recovery is critical for the
health and effective functioning of firefighters.
To this end, multiple strategies have been devised and assessed, such as partial cold water
immersion, cooling shirts, intravenous infusion of cold saline, or cool air exposure to explore the
effects of cooling on heart rate and temperature recovery from firefighting [16-20]. Cooling
shirts or vests have been demonstrated to be similar to passive cooling via cool air exposure, but
may be less effective than forearm immersion [16, 18], the efficacy of which may depend upon
the temperature of water, ambient environment, and/or the depth of hand/forearm immersion [17-
19]. However, there is also evidence suggesting there may be no difference in cooling modalities
(cooling fan, hand cooling, hand + forearm cooling, infusion of cold saline, cooling vest, or
passive cooling in temperate room) after simulated firefighting exercise in PPE [17]. Given the
importance of cooling and reducing core body temperature during rehabilitation from firefighting
coupled with uncertainty about the efficacy and practicality of cooling methods, it has been
suggested that more work is needed to understand optimal and practical cooling strategies in
firefighters [19].
Recently, a novel wearable wrist cooling device has been developed (dhamaSPORTtm,
DhamaUSA) and could be a viable cooling intervention; however, there is a paucity of
independent peer-reviewed studies of its effectiveness. To this end, Edmonds et al. studied the
impact of wrist cooling in firefighters during recovery from live firefighting training scenarios
[21]. Specifically, during rehabilitation firefighters were randomly assigned to wear a wrist
cooling band, which was either “on”, providing cooling, or “off”, providing no cooling. Despite
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trends for improved thermal comfort and improved recovery of heart rate variability, core
temperature was not measured [21]. While this study suggests that wrist cooling during recovery
might offer some relief from heat stress firefighters are exposed to, and thus potentially
beneficial for on-site rehabilitation, whether wrist cooling during recovery might improve the
return of core temperature remains unanswered.
Accordingly, the current study sought to determine the efficacy of the dhamaSPORTtm
cooling band on recovery from exercise-induced heat stress while wearing PPE in a workload-
matched and controlled environmental setting. It was hypothesized that dhamaSPORTtm cooling
band would improve recovery of heart rate and core temperature after physical work in
firefighting PPE.
Subjects and General Procedures
Eleven healthy, physically active, male participants aged 18-34 years old were recruited
by public advertisement and word of mouth from XXX and the greater XXX region in New
York. To be considered healthy, participants could not have been current or recent (<6 months)
smokers, and those with any history of cardiovascular, renal, musculoskeletal, or metabolic
diseases were excluded. Health history was collected using questionnaires (American College of
Sports Medicine Pre-Participation Screening) to assess for eligibility. To be included, and ensure
completion of the exercise protocol, participants must have been physically active, which was
defined, in accordance with ACSM, as regularly engaging in a minimum of 30 minutes of
moderate intensity aerobic activity at least 3 days a week [22]. Further, as core temperature was
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monitored using a telemetry pill, participants also completed a screening form, and any
participant with contraindications to telemetry pill use were excluded from the study.
Participants were asked to arrive rested without recent strenuous exercise (within 24 hours) and
without alcohol or caffeine for 12 hours prior. Participants were instructed to arrive >4 hours
post prandial and hydrated, to achieve hydration they were suggested to ingest 500 ml 2-3 hours
prior and 250 ml 15 minutes prior to arrival. Participants were instructed to maintain a diet
similar in macronutrient composition and caloric content for the duration of the study, and to
avoid all dietary supplements (e,g. multivitamins, etc.). All participants provided written
informed consent prior to participation. Approval for this study was granted by the Human
Subjects Institutional Review Board (IRB#1612-569) of XXX and is in accordance with the most
recent revisions of the Declaration of Helsinki. All studies were conducted in a thermoneutral
(21 ± 1°C, 29 ± 12% relative humidity), and normobaric (~750 mmHg) environment.
This study utilized a single-blind, counterbalanced, within-subjects crossover design, to
assess the recovery from exercise-induced heat stress (Experimental Overview can be seen in
Figure 1). Specifically, all subjects were randomly assigned to complete two trials, one
experimental trial and one control trial. On both days the DhamaSPORTtm cooling band was
worn during recovery, but on one day the band was not active and the other day the band was
activated (control vs. cool). In the cooling condition when the band was activated (cool
condition) it was set to the coldest setting (7°C). While we attempted to reduce possible
anticipatory responses through single blinding and not making the participants’ aware of which
condition they were receiving, when the band was active participants’ were able to detect the
cooling, but when the band was off they were unsure. The heat transfer rate (q) for this device
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ranges from 0.2-200 watts, with typical values of 0.5-50 watts, depending upon ambient
conditions. The cooling was activated prior to participants putting the band on, but is nearly
instantaneous upon activation. Study visits were scheduled to be matched for time of day on an
individual basis (range from 10am-2pm), minimally 48 hours apart, but were constrained to be
completed within 2 weeks. Participants were instructed to ingest a telemetry pill (CorTemp®
Ingestible Core Body Temperature Sensor, HQInc.) 8 hours prior to the scheduled trial time [23,
24]. To avoid potential confound of fluid intake on gastrointestinal core temperature, participants
were not allowed to consume fluids at any point during the study visit. Upon arrival, participants
height (cm), and weight (kg) were measured, and body mass index (BMI) was calculated.
Participants were then instrumented with a heart rate monitor (H7, Polar, Lake Success, NY),
presence of the telemetry pill was confirmed, and were rested for 10 minutes prior to obtaining
baseline measurements. Resting heart rate (HR), heart rate variability (HRV), core temperature
(TCore), thermal sensation (TS, 0-8 scale), rating of perceived exertion (RPE, 1-10), and visual
analog scale (VAS) for fatigue [25, 26] were measured. Over a 1 minute breathing paced period,
time domain based indices of HRV, including: root mean square of successive differences
(RMSSD), natural log transformed RMSSD (lnRMSSD), standard deviation of N-N (normal R-
R) intervals (SDNN), the number of pairs of successive N-N intervals that differ by more than 50
ms (NN50), and percent of NN50 of total NN intervals (PNN50), were measured using the Elite
HRV Application [27, 28].
After baseline measures participants donned structural personal protective firefighting
clothing (turnout coat, pants, thermal hood, helmet, gloves) and self-contained breathing
apparatus (SCBA) weighing approximately 20 kg. Based upon prior work in our lab, participants
walked on a treadmill (Trackmaster TMX428CP) for 30 minutes at 4.83 kilometers per hour and
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5% incline, which has been sufficient to induce heat stress of ~1°C in young healthy controls
[29]. During exercise HR and TCore were recorded every minute. RPE and TS were taken every 5
minutes during exercise. Upon completion, the PPE were doffed as quickly as possible, similar
to an occupational setting, the participant was then instrumented with the DhamaSPORTtm
cooling band, set to its coldest setting (~7°C), and escorted to a chair, upon sitting a timer was
started to document the time to recovery. This transition period was minimal and well-matched
between conditions HR and TCore were recorded every 30 seconds until HR recovered to within
15% of resting HR (recovery = HR<15% of HRREST). As individual differences in recovery time
were likely, upon reaching HR recovery, RPE, TS, TCore, HR, HRV, and VAS were again
Data Analysis
Statistical evaluations were completed using SPSS (SPSS v. 22.0 IBM Inc., Armonk, NY,
USA). Time to 50% recovery was calculated to determine if wrist cooling might alter the kinetics
of recovery. Time to recovery and time to 50% recovery between conditions were compared
using paired samples t-tests. To ensure participants arrived to the lab in a similar state, paired
samples t-tests were run to determine if any significant differences existed at baseline. To
quantify if the heat stress and cardiovascular strain prior to cooling was similar during exercise
between conditions, two-way repeated measures analysis of variance (condition x time) were
used to compare the HR, RPE, TS, TCore exercise responses. Further, HR, RPE, TS, TCore during
the final minute of exercise, just prior to cooling, were compared using paired samples t-tests.
The individual nadir for HR and TCore during recovery were assessed using paired samples t-
tests. Given, individual differences in time to recovery, HR, HRV indices (RMSSD, lnRMSSD,
SDNN, NN50, and PNN50), TS, Fatigue, RPE, and TCore were compared between trials, at the
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point of achieving HR recovery, using paired samples t-tests. Further, the kinetics recovery of
HR and TCore were interrogated with regression analysis. Alpha values of 0.05 were used for all
comparisons. Data are presented as means ± standard deviation.
Participants and Baseline
Participants were 11 young healthy males (23 ± 5 years, 176 ± 3 cm, 84 ± 12 kg, BMI 27
± 3 kg/m2). Baseline measures of core temperature, thermal sensation, fatigue (RPE and VAS),
HR, and HRV, were not different at the start of each trial (Table 1).
Exercise-Induced Heat Stress
No significant interaction (condition x time) or condition effects were observed in HR or
TCore throughout exercise (Figure 2, p > 0.05), though expectedly there was a main effect for time
where HR and TCore increased over time (p < 0.05). During the final minute of exercise just prior
to cooling, HR (148 ± 22 vs. 145 ±19 bpm) and TCore (37.9 ± 0.3 vs. 37.8 ± 0.3°C) were also not
different (control vs. cooling, p > 0.05). RPE and TS were also not different between trials
throughout exercise (data not shown), as no interaction (condition x time) or main effects of
condition were observed (p > 0.05), though again, expectedly there was a time effect where RPE
and TS increased over the duration of exercise (p < 0.05). During the final minute of exercise,
just prior to cooling, RPE (5 ± 1 vs. 5 ± 1) and TS (6.4 ± 0.8 vs. 6.5 ± 0.4) were not different
between trials (both, control vs. cooling, p > 0.05).
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Impact of Wrist Cooling on Recovery
Time to 50% recovery (46 ± 41 vs. 43 ± 41 sec) and time to recovery (519 ± 275 vs. 624
± 289 sec) were not significantly different with the band active (p > 0.05, control vs. cooling).
Figure 3 illustrates the TCore and HR responses throughout recovery measured every 30 seconds.
The average individual nadir HR during recovery was significantly lower with the band active
(79 ± 12 vs. 72 ± 9 bpm, p < 0.05, control vs. cooling), while the average nadir for TCore during
recovery (37.75 ± 0.3 vs. 37.63 ± 0.3 °C) only approached statistical significance (p=0.08,
control vs. cooling). Despite similar intercepts, the slope for average TCore was -0.009 vs. -
0.033°C/minute for control (off) and cooling (on), respectively, or about a 279% increase in rate
of cooling. For HR, again starting from similar intercepts, the rate of HR recovery assessed by
the slope was not different with the band activated, -4 vs. -5 bpm/minute, for control (off) and
cooling (on), respectively.
Given the individual differences in HR recovery kinetics, at the individual point of HR
recovery, with the band actively cooling, TCore was significantly lower (p < 0.05) by 0.2 °C
(Table 2). Heart rate tended to be lower as well, by 4 bpm (p = 0.06) (Table 2). However, indices
of HR variability (RMSSD, lnRMSSD, SDNN, NN50, or PNN50) were unaffected (all p > 0.05,
Table 2). Thermal sensations were unaffected, but perceptions of fatigue, RPE and VAS,
approached statistical significance with the band active (p = 0.06 and p = 0.08, for RPE and
VAS, respectively, Table 2).
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The purpose of this study was to evaluate the effects of wrist cooling on recovery from
exercise-induced heat stress (EIHS) while wearing PPE in a controlled environment with
matched workload and physiological demand. It was hypothesized that recovery time to resting
heart rate and core temperature would be shorter when the cooling band was activated. The main
findings from the current study are that use of the dhamaSPORTtm cooling band: did not impact
time to recovery, but at time of recovery; lowered core temperature (TCore) to a greater extent, but
only tended to lower heart rate, and lessen perceptions of fatigue. Wrist cooling via the
dhamaSPORTtm cooling band provided modest cooling, possibly beneficial in aiding recovery
from exercise-induced heat stress, particularly in recovery from situations where heat dissipation
is impeded by encapsulating PPE such as in firefighting scenarios.
Impact of Wrist Cooling on Physiological Recovery
Given the thermal stress firefighters face, through combination of environment, physical
work, and impaired heat dissipation core temperature can reach values 39°C or higher [1], and
the cardiovascular strain associated with the attempt to thermoregulate could be contributory in
the prevalence of acute cardiovascular events after firefighting [30]. To mitigate this
physiological stress, multiple interventions have been devised and assessed in terms of their
efficacy in cooling and recovering heart rate after firefighting [16-20]. However, as some of
these methods are invasive (i.e. cold saline IV infusion), and some are impractical (e.g. cold
water immersion) or minimally effective, the search for cooling alternatives remains resolute
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In the present study, starting from similar baselines (Table 1) coupled with matching of
workload, the physiological responses to exercise (i.e. HR and TCore) were expectedly similar
between conditions (Figure 2). Thus, any differences observed during the recovery period were
not due to differences in baseline, exercise stimulus, or response between days as trials were
counterbalanced. In these contexts, in contrast to our hypothesis, the kinetics of HR recovery
were not meaningfully different, despite trends for a lower HR during recovery (Figure 3) and
lower nadir HR during recovery period. In contrast to the study of Edmonds et al. [21], we did
not find an impact of wrist cooling via the dhamaSPORTtm cooling band on any measure of heart
rate variability, but did find that HR was ~5bpm lower at recovery and approached statistical
significance (p=0.06). While the mechanisms responsible this disparity are not readily apparent,
in the prior study, HR during recovery, on average, never fell below 100 bpm during the 15
minutes of rehabilitation, likely due to higher ambient temperatures, and HR variability was only
obtained on a subset (n=10) [21], perhaps complicating such comparison. In comparison to other
work, Barr et al. found that HR was lower during recovery with forearm immersion or combined
with a cooling vest, but not cooling vest alone or control [18]. However, a comparison of
multiple active cooling strategies from exercise-induced heat stress found that arm or hand
immersion, fan, cold IV saline, and cooling vest were not different from passive cooling via
room temperature in terms of heart rate recovery [17]. Although, both aforementioned studies
were lab based exercises, but in agreement in live fire training settings forearm immersion HR
recovery was also found to be not different [16]. Thus, the wrist cooling method employed in the
current study might not affect the rate of HR recovery, per se, but might result in lower HR at
recovery perhaps better preparing individuals for subsequent bouts of activity.
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Similar to HR, TCore was also trending for greater resolution with wrist cooling towards
baseline, as evidenced in the steeper slope (Figure 3) and trend for lower nadir observed during
recovery. However, TCore was significantly lower at the point of recovery (Table 2), and as time
to recovery was not different, these paired observations are supportive of a greater rate of
recovery. As the Edmonds et al. study did not measure core temperature [21], thus the current
study is the first to document the potential cooling effects of the dhamaSPORTtm cooling band.
Though, the exercise-induced heat stress elicited by a single moderate duration bout, while
significantly higher than resting, was relatively modest as compared to other studies with
multiple bouts ranging from 20-40 minutes [16-18]. Thus, the relatively lower starting point of
core temperature might explain the on average lower rate of cooling elicited by the band (-
0.033°C/min) when compared to previous studies (0.04-0.06 °C/min) [17]. The multiple
differences (e.g. exercise intensity, environment, number and length of bouts, and thus degree of
EIHS) makes direct comparisons between studies problematic. In the context of the current
study, the dhamaSPORTtm cooling band did tend to increase the rate of cooling and thus lowered
the core temperature observed at recovery.
Relatedly, Edmonds et al. [21] reported that thermal comfort and sensation were lower
after 5 and 10 minutes with the dhamaSPORTtm cooling band on, respectively. The sustained HR
and greater improvement in thermal comfort might be due to the on average warmer and more
humid ambient conditions in which the Edmonds et al. study was conducted [21]. In the current
study, we extend these findings by including measures of fatigue, and report that both categorical
(RPE) and continuous (VAS) reports of fatigue were lower (p=0.06-0.08) with the cooling band
activated. The current findings complement the previous work by Edmonds et al. [21] who
demonstrated that use of the dhamaSPORT cooling band enhanced recovery and thermal comfort
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in a live-fire scenario. The improved thermal comfort with wrist cooling may be the result of
relatively dense population of sensory afferent neurons at the wrist and specifically the transient
receptor potential melastatin 8 (TRPM8), the canonical cold and menthol sensitive receptor,
activation of which has been shown to reduce thermal sensation during exercise in the heat [31].
This portable, lightweight, wrist cooling device modestly impacted recovery of heart rate,
core temperature, and lessened sensations of fatigue after exercise-induced heat stress. Given
cost of implementation, coupled with forearm ice water immersion being at least equally
effective, and perhaps superior, the cost-benefit ratio for on-scene rehabilitation may favor ice
water immersion. Though, wrist cooling devices might provide continued additional cooling in
transfer back to the station, when ice water immersion is perhaps impractical. Populations other
than firefighters may also benefit from this wrist cooling device, such as clinical populations
who may be heat sensitive, for example patients with multiple sclerosis [32, 33] or spinal cord
injury [34]; however controlled work is needed to determine if this device is beneficial in these
populations. Future studies might explore if such devices may aide in carrying out activities of
daily living in such populations.
In summary, the results of the current study demonstrate for the first time the efficacy of
the novel wrist cooling device in reducing core temperature, heart rate, and fatigue in an
occupationally relevant model of exercise-induced heat stress. These findings suggest wrist
cooling only provides modest effects on recovery from exercise-induced heat stress in young
healthy males.
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ACKNOWLEDGEMENTS: The authors would like to thank those who graciously volunteered
for the study and the Faculty Student Summer Research Program for supporting student work
(XXX and XXX).
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Copyright © 2018 American College of Occupational and Environmental Medicine. Unauthorized reproduction of this article is prohibited
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Copyright © 2018 American College of Occupational and Environmental Medicine. Unauthorized reproduction of this article is prohibited
Table 1. Comparison of baseline core temperature, cardiovascular, and perceptual measures
Variable OFF ON Significance
Core Temperature (C) 37.3 ± 0.3 37.3 ± 0.4 N.S.
Heart Rate (bpm) 67 ± 11 62 ± 8 N.S.
Thermal Sensation 3.5 ± 0.8 3.6 ± 0.9 N.S.
Rating of Perceived Exertion 1.2 ± 0.4 1.3 ± 0.5 N.S.
Fatigue (VAS) 0.6 ± 0.8 0.6 ± 0.9 N.S.
RMSSD (ms) 97 ± 68 119 ± 61 N.S.
LnRMSSD 4.5 ± 0.8 4.7 ± 0.6 N.S.
SDNN (ms) 143 ± 72 153 ± 78 N.S.
NN50 28 ± 13 32 ± 14 N.S.
PNN50 (%) 42± 21 50 ± 20 N.S.
Mean ± standard deviation
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Copyright © 2018 American College of Occupational and Environmental Medicine. Unauthorized reproduction of this article is prohibited
Table 2. Comparison of post-recovery core temperature, cardiovascular, and perceptual
Variable OFF ON Significance
Core Temperature (C) 37.8 ± 0.3 37.6 ± 0.3 p=0.03
Heart Rate (bpm) 75 ± 12 71 ± 10 p=0.06
Time to Recovery (s) 519 ± 46 624 ± 59 N.S.
Time to 50% Recovery (s) 46 ± 41 43 ± 41 N.S.
Thermal Sensation 3.7 ± 0.8 3.8 ± 0.9 N.S.
Rating of Perceived Exertion 2.7 ± 1.4 2.3 ± 1.5 p=0.06
Fatigue (VAS) 2.9 ± 2 2.5 ± 2 p=0.08
RMSSD (ms) 84 ± 59 78 ± 44 N.S.
LnRMSSD 4.1 ± 0.9 4.2 ± 0.6 N.S.
SDNN (ms) 113 ± 61 109 ± 49 N.S.
NN50 21 ± 16 23 ± 12 N.S.
PNN50 (%) 31± 25 33 ± 20 N.S.
Mean ± Standard Deviation
... In firefighter research, many different portable HRV monitoring systems have been used while firefighters are on duty to complete simulation protocols or to discern the physiological burden placed upon the cardiovascular system by firefighting (Biéchy et al., 2021;Marcel-Millet, Groslambert, Gimenez, Grosprêtre, & Ravier, 2021;Marciniak, Wahl, & Ebersole, 2021;Robertson et al., 2017;Schlicht et al., 2018). The most restricting HRV monitor appears to be the VitalJacket®. ...
... Firefighting, an often laborious and dangerous occupation, places many firefighters in harm's way due to the accompanying heat stress, dehydration, and physical exertion. The combination of these factors may cause acute sympathetic activation in firefighters (Larsen, Snow, & Aisbett, 2015;Pluntke, Gerke, Sridhar, Weiss, & Michel, 2019;Schlicht et al., 2018;Shin et al., 2016). However, as recommended by many researchers, policy makers, and fire departments, regular physical activity provides a cardioprotective effect, such as bradycardia, and improved cardiovascular fitness. ...
... The study highlighted the versatility of using HRV in determining the usefulness in using various recovery measures in firefighters. Schlicht et al. (2018) investigated the effect of wrist cooling on recovery in firefighters, using HRV (Polar H7 heart rate monitor) as the recovery indicator. Although the study did not find a significance using HRV as an indicator of recovery, it did share a similar result of non-significance with rating of fatigue. ...
Firefighters are required to maintain all aspects of their health and wellness in order to sustain their fitness for duty. Heart rate variability (HRV) has been used as a reliable tool when assessing the stressors placed on firefighters, be it physical, emotional, or psychological. This review determined the usefulness of using HRV as a tool to determine the physical, physiological, and psychological health of firefighters at a more regular and frequent scale. HRV is a versatile technology with a plethora of uses, particularly in monitoring the cardiovascular strain as a result of firefighting and recovery post-fire suppression. In addition, the literature showed that HRV could be used to successfully monitor physical fitness, physiological stress, psychological stress, decision making, risk taking behavior and recovery in firefighters. The use of mobile technology measuring HRV may be used to successfully assess firefighter occupational performance. In future research, longitudinal studies investigating HRV use in firefighters are warranted.
... Recently, a company has developed a wearable, active cooling method (dhamaSPORT tm , DhamaUSA, Scotts Valley, CA, USA) that is light weight (115 g, 6 cm wide) and can be worn on the wrist during activity while posing minimal disruption or burden to the athlete (e.g., ice vest). While we have demonstrated that this wrist cooling device improved physiological recovery and reduced fatigue from an occupationally relevant model of exercise-induced heat stress [10], it has yet to be determined whether wrist percooling is capable of improving endurance performance in the heat, and if this might impact post-exercise recovery. Aside from the obvious potential to provide cooling, mitigating exercise-induced elevations in core temperature, surface percooling might activate the transient receptor potential melastatin 8 (TRPM8) "cold receptor", which might alter thermal sensation and/or exercise performance [11]. ...
... After 10 min of quiet rest, a one minute [18], breathing frequency paced [19], recording of heart rate (HR) and R-R intervals were obtained via HR monitor, sent to a mobile device (IPad Pro, Apple, Cupertino, CA, USA) via Bluetooth™ and analyzed by a mobile device application (Elite HRV, Gloucester, MA, USA). The Elite HRV application performs artifact correction and has been shown to be valid [20] and has been used in previous studies [10,[20][21][22]. Specifically, along with mean HR, R-R intervals were analyzed for the standard deviation of R-R intervals, SDNN; root mean square of successive differences, RMSSD; and the log transformed RMSSD, LnRMSSD. ...
... A prior meta-analytical review demonstrated that more aggressive cooling methods, such as whole body cooling likely help to recover performance [42], though few studies have focused on recovery of core temperature. Much of this work has been done in occupational models, such as firefighting, using multiple interventions, some invasive, to induce cooling and recovery of heart rate after firefighting [43][44][45][46][47]. Accordingly, our previous work using this wrist cooling device to induce cooling after an occupational model of exercise-induced heat stress via exercise in encapsulating clothing, revealed a significant positive impact of wrist cooling on recovery of temperature and heart rate [10]. However, in that study the exercise was necessarily more modest (walking) and shorter, thus the rise in core temperature was lower, all only increasing by 1 • C or less, potentially creating multiple differentials between the present and the aforementioned study. ...
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Environmental heat stress poses significant physiological challenge and impairs exercise performance. We investigated the impact of wrist percooling on running performance and physiological and perceptual responses in the heat. In a counterbalanced design, 13 trained males (33 ± 9 years, 15 ± 7% body fat, and maximal oxygen consumption, VO 2 max 59 ± 5 mL/kg/min) completed three 10 km running time trials (27 • C, 60% relative humidity) while wearing two cooling bands: (1) both bands were off (off/off), (2) one band on (off/on), (3) both bands on (on/on). Heart rate (HR), HR variability (HRV), mean arterial pressure (MAP), core temperature (T CO), thermal sensation (TS), and fatigue (VAS) were recorded at baseline and recovery, while running speed (RS) and rating of perceived exertion (RPE) were collected during the 10 km. Wrist cooling had no effect (p > 0.05) at rest, except modestly increased HR (3-5 ∆beats/min, p < 0.05). Wrist percooling increased (p < 0.05) RS (0.25 ∆mi/h) and HR (5 ∆beats/min), but not T CO (∆ 0.3 • C), RPE, or TS. Given incomplete trials, the distance achieved at 16 min was not different between conditions (off/off 1.96 ± 0.16 vs. off/on 1.98 ± 0.19 vs. on/on 1.99 ± 0.24 miles, p = 0.490). During recovery HRV, MAP, or fatigue were unaffected (p > 0.05). We demonstrate that wrist percooling elicited a faster running speed, though this coincides with increased HR; although, interestingly, sensations of effort and thermal comfort were unaffected, despite the faster speed and higher HR.
... As an example, current guidelines in New South Wales, Australia (NSW) instruct that after the depletion of one to two breathing apparatus cylinders or 20-40 min of intense work, firefighters should rest and rehydrate, however these recommendations are due for review (Fire and Rescue NSW, 2010). Previous research on cooling strategies to relieve heat strain have indicated that forearm/wrist cooling (Barr et al., 2009;Schlicht et al., 2018), ice slushy ingestion (Walker et al., 2014) and cold water immersion (Walker et al., 2014) show small to moderate effectiveness in reducing core temperature and recovery of other physiological parameters from simulated fire-fighting activities (although data on physical and cognitive performance is limited). This evidence, and others (Brearley and Walker, 2015), has led to various recommendations on best practice for cooling in these populations (e.g. ...
... no fridges/ice machines on trucks). There is some evidence to indicate the efficacy of these suggested strategies (forearm/wrist cooling (Barr et al., 2009;Schlicht et al., 2018), ice slushy ingestion (Walker et al., 2014) and cold water immersion (Walker et al., 2014)) in reducing core temperature, although results vary across environmental conditions, task exposure and experimental designs (Brearley and Walker, 2015). ...
Objectives The aim of this study was to assess current perceptions of heat stress, fatigue and recovery practices during active duty in Australian firefighters. Design Prospective survey. Methods 473 firefighters from Fire and Rescue New South Wales completed a two-part, 16-item survey. Questions included perceptions of the operational activities and body areas associated with the most heat stress, the most mentally and physically demanding activities, and levels of fatigue felt. Further questions focussed on the use and importance of recovery practices, effectiveness of currently used heat-mitigation strategies and additional cooling strategies for future use. Results Around a third of firefighters (62%) reported structural fire-fighting as the hottest operational activities experienced, followed by bushfire-fighting (51%) and rescue operations (38%). The top three responses for which body-parts get the hottest ranked as ‘the head’ (58%), ‘the whole body’ (54%) and ‘the upper back’ (40%), respectively. The majority of firefighters (~90%) stated they always or sometimes use the opportunity to recover at an incident, with the top three being ‘sit in the shade’ (93%), ‘cold water ingestion (drinking)’ (90%) and ‘removing your helmet, flash hood and jacket’ (89%). Firefighters reported higher usefulness for more easily deployed strategies compared to more advanced strategies. Limited age and gender differences were found, although location of active service differences were present. Conclusion These findings may inform future research, and translation to operational directives for recovery interventions; including exploration of protective gear and clothing, education, resources and provision of cooling methods, as well as recovery aid development.
... Accordingly, Schlicht and colleagues found negligible improvements of wrist cooling on core temperature during recovery from exercise-induced heat stress from wearing firefighting protective equipment. 37 Further consideration and caution must be considered, bearing in mind that some of these garments seem to only create a perception of cooling without core temperature decrease. 34 Several companies have created new cooling wearable technologies during the last year, with some of the most novel and promising summarised in table 1. ...
Full-text available
The Tokyo 2020 Olympic Games is expected to be among the hottest Games in modern history, increasing the chances for exertional heat stroke (EHS) incidence, especially in non-acclimatised athletes/workers/spectators. The urgent need to recognise EHS symptoms to protect all attendees’ health has considerably accelerated research examining the most effective cooling strategies and the development of wearable cooling technology and real-time temperature monitoring. While these technological advances will aid the early identification of EHS cases, there are several potential ethical considerations for governing bodies and sports organisers. For example, the impact of recently developed cooling wearables on health and performance is unknown. Concerning improving athletic performance in a hot environment, there is uncertainty about this technology’s availability to all athletes. Furthermore, the real potential to obtain real-time core temperature data will oblige medical teams to make crucial decisions around their athletes continuing their competitions or withdraw. Therefore, the aim of this review is (1) to summarise the practical applications of the most novel cooling strategies/technologies for both safety (of athletes, spectators and workers) and performance purposes, and (2) to inform of the opportunities offered by recent technological developments for the early recognition and diagnosis of EHS. These opportunities are presented alongside several ethical dilemmas that require sports governing bodies to react by regulating the validity of recent technologies and their availability to all.
Objectives Due to the nature of firefighting, most effective cooling interventions to reduce heat strain and optimise performance are not practically viable. This study quantified the effects of two practical cooling strategies, co-designed with subject-matter experts, on physiological strain and physical, perceptual, and visuo-motor performance during simulated firefighting in the heat. Design Randomised cross-over. Methods On three occasions 14 firefighters completed an 80-min simulation in a hot-humid environment (32.0[0.9]°C, 59[3]%RH) including two 20-minute firefighting tasks in full protective clothing, each followed by 20-minutes seated recovery. Recovery involved removal of protective clothing and one of three interventions – control (CON; ambient-temperature water consumption), basic (BASIC; cool-water consumption, ambient-forearm immersion/towels, fan), and advanced (ADV; ice-slushy consumption, cool-forearm immersion/ice packs, misting-fan). Thermal (core temperature) and cardiovascular (heart rate, arterial pressure) responses were measured throughout, whilst physical (handgrip/balance), visuo-motor (reaction time/memory recall) and perceptual (fatigue/thermal sensation/comfort) measures were assessed pre- and post-trial. Results Compared to CON, core temperature was lower in BASIC and ADV following the second task (ADV: 37.7[0.4]; BASIC: 38.0[0.4]; CON: 38.3[0.4]°C) and recovery protocol (ADV: 37.5[0.3]; BASIC: 37.7 [0.3] CON: 38.3[0.4]°C). This was paralleled by lowered heart rate, rate pressure product, and thermal sensation following the recovery protocols, in the ADV and BASIC condition compared to CON (p < .05). No physical or visuo-motor outcomes differed significantly between conditions. Conclusion Whilst these observations need to be extended to field conditions, our findings demonstrate that two novel cooling interventions developed in collaboration with subject-matter experts offered benefits for reducing thermal strain and optimising firefighter safety.
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Purpose: The study investigated the effect of a non-thermal cooling agent, L-menthol, on exercise at a fixed subjective rating of perceived exertion (RPE) in a hot environment. Method: Eight male participants completed two trials at an exercise intensity between 'hard' and 'very hard', equating to 16 on the RPE scale at ~35 °C. Participants were instructed to continually adjust their power output to maintain an RPE of 16 throughout the exercise trial, stopping once power output had fallen by 30%. In a randomized crossover design, either L-menthol or placebo mouthwash was administered prior to exercise and at 10 min intervals. Power output, [Formula: see text]O2, heart rate, core and skin temperature was monitored, alongside thermal sensation and thermal comfort. Isokinetic peak power sprints were conducted prior to and immediately after the fixed RPE trial. Results: Exercise time was greater (23:23 ± 3:36 vs. 21:44 ± 2:32 min; P = 0.049) and average power output increased (173 ± 24 vs. 167 ± 24 W; P = 0.044) in the L-menthol condition. Peak isokinetic sprint power declined from pre-post trial in the L-menthol l (9.0%; P = 0.015) but not in the placebo condition (3.4%; P = 0.275). Thermal sensation was lower in the L-menthol condition (P = 0.036), despite no changes in skin or core temperature (P > 0.05). Conclusion: These results indicate that a non-thermal cooling mouth rinse lowered thermal sensation, resulting in an elevated work rate, which extended exercise time in the heat at a fixed RPE.
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Increases in oxidative stress or decreases in antioxidant capacity, or redox imbalance, are known to alter physiological function and has been suggested to influence performance. To date, no study has sought to manipulate this balance in the same participants and observe the impact on physiological function and performance. Using a single-blind, placebo-controlled, and counterbalanced design, this study examined the effects of increasing free radicals, via hyperoxic exposure (FiO2 = 1.0), and/or increasing antioxidant capacity, through consuming an antioxidant cocktail (AOC; vitamin-C, vitamin-E, α-lipoic acid), on 5-kilometer (km) cycling time-trial performance, and the physiological and fatigue responses in healthy college-aged males. Hyperoxic exposure prior to the 5 km TT had no effect on performance, fatigue, or the physiological responses to exercise. The AOC significantly reduced average power output (222 ± 11 vs. 214 ± 12 W), increased 5 km time (516 ± 17 vs. 533 ± 18 sec), suppressed ventilation (VE; 116 ± 5 vs. 109 ± 13 L/min), despite similar oxygen consumption (VO2; 43.1 ± 0.8 vs. 44.9 ± 0.2 mL/kg per min), decreased VE/VO2 (35.9 ± 2.0 vs. 32.3 ± 1.5 L/min), reduced economy (VO2/W; 0.20 ± 0.01 vs. 0.22 ± 0.01), increased blood lactate (10 ± 0.7 vs. 11 ± 0.7 mmol), and perception of fatigue (RPE; 7.39 ± 0.4 vs. 7.60 ± 0.3) at the end of the TT, as compared to placebo (main effect, placebo vs. AOC, respectively). Our data demonstrate that prior to exercise, ingesting an AOC, but not exposure to hyperoxia, likely disrupts the delicate balance between pro- and antioxidant forces, which negatively impacts ventilation, blood lactate, economy, perception of fatigue, and performance (power output and 5 km time) in young healthy males. Thus, caution is warranted in athletes taking excess exogenous antioxidants.
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The introduction of smart phone applications has allowed athletes and practitioners to record and store R-R intervals on smart phones for immediate heart rate variability (HRV) analysis. This user-friendly option should be validated in the effort to provide practitioners confidence when monitoring their athletes before implementing such equipment.The objective of this investigation was to examine the relationship and validity between a vagal related HRV index, rMSSD when derived from a smart phone application accessible with most operating systems against a frequently utilized computer software program, Kubios HRV 2.2R-R intervals were recorded immediately upon awakening over 14 consecutive days using the Elite HRV smartphone application. R-R recordings were then exported into Kubios HRV 2.2 for analysis. The relationship between rMSSDln derived from Elite HRV and Kubios HRV 2.2 was examined using a Pearson Product Moment Correlation and a Bland-Altman Plot.An extremely large relationship was identified (r = 0.92; p < 0.0001; CI 95% = 0.90;0.93). A total of 6.4% of the residuals fell outside of the 1.96 ±SD (CI 95% = -12.0%; 7.0%) limits of agreement. A negative bias was observed (mean: -2.7%; CI 95% = -3.10%;-2.30%) whose CI 95% failed to fall within the line of equality.Our observations demonstrated differences between the two sources of HRV analysis. However, further research is warranted as this smartphone HRV application may offer a reliable platform when assessing parasympathetic modulation.
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Background Firefighting is a highly stressful occupation with unique physical challenges, apparel and environments that increase the potential for dehydration. Dehydration leaves the firefighter at risk of harm to their health, safety and performance. The purpose of this review was to critically analyse the current literature investigating the impact of fighting ‘live’ fires on firefighter hydration. MethodsA systematic search was performed of four electronic databases for relevant published studies investigating the impact of live fire suppression on firefighter hydration. Study eligibility was assessed using strict inclusion and exclusion criteria. The included studies were critically appraised using the Downs and Black protocol and graded according to the Kennelly grading system. ResultsTen studies met the eligibility criteria for this review. The average score for methodological quality was 55 %, ranging from 50 % (‘fair’ quality) to 61 % (‘good’ quality) with a ‘substantial agreement’ between raters (k = .772). Wildfire suppression was considered in five studies and structural fire suppression in five studies. Results varied across the studies, reflecting variations in outcome measures, hydration protocols and interventions. Three studies reported significant indicators of dehydration resulting from structural fire suppression, while two studies found mixed results, with some measures indicating dehydration and other measures an unchanged hydration status. Three studies found non-significant changes in hydration resulting from wildfire firefighting and two studies found significant improvements in markers of hydration. Ad libitum fluid intake was a common factor across the studies finding no, or less severe, dehydration. Conclusions The evidence confirms that structural and wildfire firefighting can cause dehydration. Ad libitum drinking may be sufficient to maintain hydration in many wildfire environments but possibly not during intense, longer duration, hot structural fire operations. Future high quality research better quantifying the effects of these influences on the degree of dehydration is required to inform policies and procedures that ensure firefighter health and safety.
Introduction: Best practice recommendations suggest five days of short term heat acclimation (STHA) prior to multi-bout exercise days to reduce risk of exertional heat illnesses. It is unknown if five days of STHA is sufficient to mitigate thermal strain and protect against EHI. Purpose: To determine lasting physiological effects of exercise in heat on subsequent exercise before and after STHA. Methods: Eighteen men (age: 22 ± 3 y, height: 180.0 ± 6.0 cm, weight: 74.24 ± 7.42 kg, body fat: 9.4 ± 4.1%, maximal oxygen consumption: 54.6 ± 5.1 ml·kg-1·min-1) performed two intermittent treadmill exercise sessions two hours apart, followed by one session the following day (40°C, 40% relative humidity). Three additional days of STHA consisted of 90 minutes of exercise in the same environment. Subjects again completed a double exercise session followed by a single session the following day. Heart rate (HR), rectal temperature (Tre), and perceptual scales were assessed throughout exercise. Environmental symptoms and blood variables were assessed Pre- and Post-exercise. Results: Before STHA, resting HR and Tre were lower before Bout 1 (80 ± 12 bpm, 36.79 ± 0.44°C) compared to Bout 2 (103 ± 17 bpm, p < 0.001; 37.06 ± 0.50°C, p = 0.038) but were similar to Day 2 (81 ± 13 bpm, p = 0.728; 36.80 ± 0.32°C, p = 0.924), respectively. Exercising HR and Tre were similar between Bouts 1 and 2 despite a shorter exercise duration during Bout 2 (93 ± 27 min) than Bout 1 (120 ± 0 min, p < 0.001). Rate of Tre rise was greater during Bout 2 (0.031 ± 0.011°C·min-1) than Bout 1 (0.023 ± 0.004°C·min-1, p = 0.011). The STHA protocol induced a partially acclimated state, indicated by decreased exercising Tre, HR, thermal sensation, and perceived exertion (p < 0.05). Both Pre- and Post-STHA, many participants were unable to complete the full exercise protocol due to elevated Tre, environmental symptoms, and fatigue. Conclusion: Multi-bout exercise on the first of two sequential days led to a higher resting level of fatigue and premature cessation of exercise during the second bout of exercise both Pre- and Post-STHA.
Background The United States Fire Administration (USFA) provides high-quality data for firefighter deaths (FFDs), but until now this data has not been analyzed for temporal trends. This analysis explores FFDs between 1990–2016 to determine high risk groups for outreach and training. Methods Mortality rates were calculated using USFA information compared against the total number of deaths per-year. Rates were compared between 1990–2009 (early period) and 2010–2016 (recent period). Multinomial logistic regression was used to determine predictors of death in firefighters by age group (≤45 yrs. old and >45) and by work status (career vs volunteer). Results Analysis of 3159 FFDs revealed a decline in crude-rate mortality between 1990–2009 and 2010–2016 (47.4 vs 35 FF deaths/million, p<0.0001). Firefighters ≤45 yrs. old were less likely to die in the 2010s than in the 1990s-2000’s, (13.7 vs 24.7 FF deaths/million, p=0.0002). Trauma related deaths decreased (13.1 vs 8.1, p=0.0003) while CV-related deaths remained constant (19.4 vs 19.5, p=0.24). Regression analysis determined that volunteer firefighters were more likely to die from burns (OR 1.7, CI:1.2–2.4, P<0.0001) and trauma (OR 1.8, CI:1.5–2.2, p<0.0001) than career firefighters. Younger firefighters were also more likely to die from burns (OR 10.4, CI 6.9–15.6, P<0.0001) and trauma (OR 6.5, CI:5.4–7.8, p<0.0001). Conclusions Although overall FFDs were lower after 2010, younger and volunteer firefighters saw an increase in burn and trauma related mortality. Cardiovascular related fatalities were consistent throughout the study. Future research should continue to make use of high-standard data to track FFDs and efficacy of interventions.
Background: The occupation of firefighting is strenuous and dangerous. Firefighters perform demanding work while wearing heavy, insulative PPE. Thus, heat stress is a constant concern. The fire service has protocols to allow for rest, rehydration, and cooling. However, finding cooling techniques that are effective and convenient remains a challenge for many departments. The aim of this study was to determine the effectiveness of a novel cooling device during firefighting training drills. Methods: Firefighters reported to REHAB during a day-long training class, and were randomly assigned to wear the dhamaSPORT cooling band in cooling mode or off mode. During the required REHAB, heart rate and perceived measures of comfort were assessed on 41 volunteer firefighters. Additionally, a subgroup of 12 firefighters wore a continuous heart rate monitoring system to assess autonomic balance changes during cooling vs. control. Results: There was a significant reduction in the perceptual measures when wearing the cooling band, and there is enhanced improvement of the autonomic nervous system balance evidenced by a decrease in RMSSD, indicating a decrease in parasympathetic tone following firefighting. However, this reduction was less in the cooling group. The results of this study indicate that the wearable cooling band improves perceptual measures and hastens autonomic nervous system recovery. Additional testing is warranted to assess the long-term impact on firefighters' health and recovery from firefighting duties, training, or actual fire calls.
Heat stress increases cardiovascular strain and is of particular concern in occupations, such as firefighters, where individuals are required to perform strenuous work while wearing personal protective equipment (PPE). Sudden cardiac events are associated with strenuous activity and are the leading cause of duty-related death among firefighters, accounting for ∼50% of duty-related fatalities/year. Understanding the acute effects of exercise-induced heat stress (EIHS) on vascular endothelial function may provide insight into mechanisms precipitating acute coronary events in firefighters. Therefore, the purpose of this study was to determine the effects of EIHS on vascular endothelial function. METHODS: Using a balanced crossover design, 12 healthy males performed 100 min of moderate-intensity, intermittent exercise with and without EIHS (PPE or cooling vest, respectively). Measurements of flow-mediated dilation (FMD), reactive hyperemia (RH), and shear rate area under the curve (SRAUC) were performed pre- and post-exercise. RESULTS: During EIHS, core temperature was significantly higher (38±0.1 vs. 37±0.1°C). Post-exercise FMD tended to be suppressed in both conditions, but was not different from pre-exercise. RH was reduced following no-EIHS but was increased following EIHS. Thus, normalizing FMD to the shear stimulus (FMD/SRAUC) revealed a significant reduction in FMD following EIHS only (Pre: 0.15±0.04 and 0.13±0.02 vs. post: 0.13±0.02 and 0.06±0.02 s−1, no-EIHS vs. EIHS, respectively). CONCLUSION: Moderate heat stress superimposed on moderate-intensity exercise resulted in reduced vascular endothelial function. This heat stress-induced alteration in the shear-dilatory relationship may relate to increased risk of acute coronary events associated with activities that combine physical exertion and heat stress (i.e. firefighting).
Introduction: Firefighters experience significant heat stress while working with heavy gear in a hot, humid environment. This study compared the cooling effectiveness of immersing the forearms and hands in 10 and 20 degrees C water. Methods: Six men (33 :+/- 10 yr; 180 +/- 4 cm; 78 +/- 9 kg; 19 +/- 5% body fat) wore firefighter 'turn-out gear' (heavy clothing and breathing apparatus weighing 27 kg) in a protocol including three 20-min exercise bouts (step test, 78 W, 40 degrees C air, 40% RH) each followed by a 20-min rest/cooling (21 degrees C air); i.e., 60 min of exercise, 60 min of cooling. Turn-out gear was removed during rest/cooling periods and subjects either rested (Control), immersed their hands in 10 or 20'C water (H-1 0, H-20), or immersed their hands and forearms in 10 or 20 degrees C water (HF-10, HF-20). Results: In 20 degrees C water, hand immersion did not reduce core temperature compared with Control; however, including forearm immersion decreased core temperature below Control values after both the second and final exercise periods (p < 0.001). In 10 degrees C water, adding forearm with hand immersion produced a lower core temperature (0.8 degrees C above baseline) than all other conditions (1.1 to 1.4 degrees C above baseline) after the final exercise period (p < 0.001). Sweat loss during Control 0 458 g) was greater than all active cooling protocols (1146 g) (p < 0.001), which were not different from each other. Discussion: Hand and forearm immersion in cool water is simple, reduces heat strain, and may increase work performance in a hot, humid environment. With 20'C water, forearms should be immersed with the hands to be effective. At lower water temperatures, forearm and/or hand immersion will be effective, although forearm immersion will decrease core temperature further.
Objective: The objective of this study was to retrospectively investigate aspects of medical monitoring, including medical complaints, vital signs at entry, and vital sign recovery, in firefighters during rehabilitation following operational firefighting duties. Results: Incident scene rehabilitation logs obtained over a 5-year span that included 53 incidents, approximately 40 fire departments, and more than 530 firefighters were reviewed. Only 13 of 694 cases involved a firefighter reporting a medical complaint. In most cases, vital signs were similar between firefighters who registered a complaint and those who did not. On average, heart rate was 104 ± 23 beats·min(-1), systolic blood pressure was 132 ± 17 mmHg, diastolic blood pressure was 81 ± 12 mmHg, and respiratory rate was 19 ± 3 breaths·min(-1) upon entry into rehabilitation. At least two measurements of heart rate, systolic blood pressure, diastolic blood pressure, and respiratory rate were obtained for 365, 383, 376, and 160 cases, respectively. Heart rate, systolic and diastolic blood pressures, and respiratory rate decreased significantly (p < 0.001) during rehabilitation. Initial vital signs and changes in vital signs during recovery were highly variable. Conclusions: Data from this study indicated that most firefighters recovered from the physiological stress of firefighting without any medical complaint or symptoms. Furthermore, vital signs were within fire service suggested guidelines for release within 10 or 20 minutes of rehabilitation. The data suggested that vital signs of firefighters with medical symptoms were not significantly different from vital signs of firefighters who had an unremarkable recovery.