ACKNOWLEDGEMENTS
• NIOSH• SunshineERC• Students,facultyandstaffatUSF• Researchcollaborators:
– Dr.ThomasE.Bernard– Dr.EricCoris– Dr.RebeccaLopez
• Introductiontoacclimatization• Physiologicaladaptationsofacclimatization• Howlongtoacclimatize?• Whataboutdecayofacclimatization?• Howlongtore-acclimatizeafterabsence?• Acclimatization/Re-acclimatizationGuidelines
EXERTIONAL HEAT ILLNESS
• Exertionalheatillnessisariskforworkersinhotenvironments.
Fatalillnesses(n=14)
Nonfatalillnesses(n=11)
Totalsample(n=25)
Unacclimatizedn(%)
11(78.6) 1(9.1) 12(48.0)
TustinAW,LamsonGE,JacklitschBL,etal.EvaluationofOccupationalExposureLimitsforHeatStressinOutdoorWorkers—UnitedStates,2011–2016.MMWRMorbMortalWklyRep2018;67:733–737.
PHYSIOLOGY OF ACCLIMATIZATION: HEART RATE
• Decreasedheartrateforagivenintensity• Increasedplasmavolume• Increasedstrokevolume• Increasedskinbloodflow
130
135
140
145
150
155
160
1 2 3 4 5 6 7 8
HeartR
ate
DaysofAcclimatization
HeartRate
PHYSIOLOGY OF ACCLIMATIZATION: CORE TEMPERATURE
• Decreasedcoretemperatureforagivenworkload• Decreasedthresholdfortheonsetofsweating
38
38.1
38.2
38.3
38.4
38.5
1 2 3 4 5 6 7 8
CoreTem
perature
DaysofAcclimatization
CoreTemperature
PHYSIOLOGY OF ACCLIMATIZATION: SWEAT RATE
• Greatersweatrate• Moredilutesweat• Sweatatalowercoretemperature
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1 2 3 4 5 6 7 8 9 10
SweatLoss(L/hr)
DaysofAcclimatization
SweatRatewithAcclimtization
AND…
• Decreasedperceivedexertion• Reducedoxygendemandatagivenintensity• Fitnessconfersanadvantagetoacclimatization
CURRENT ACCLIMATIZATION GUIDELINES
• OccupationalSafetyandHealthAdministration:– 5daysbeginningwith50%;increaseto100%byday5
• NationalInstituteforOccupationalSafetyandHealth:– 5daysbeginningwith20%;increase20%eachday
• MiningSafetyandHealthAdministration– 6daysbeginningwith50%;increase20%eachday
• Militaryguidelines– 2weeks
HOW LONG TO ACCLIMATIZE?
• n=18• Evidenceofacclimatization=plateauincoretemperatureoverlast30minutesfor3days
• à6daysforacclimatization
36
36.5
37
37.5
38
38.5
39
39.5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120
Tre
time
Tre- Acclimation-S7
Tre 1 Tre 2 Tre 3 Tre 4 Tre 5 Tre 6 Tre7 Tre 8
• Adaptationsinheartrateandcoretemperatureoccurin5dayswithdailyheatexposure.– Increaseddurationofdailyheatexposureimprovescoretemperatureadaptations.
– IncreasedWBGTimprovessweatrateadaptations.
SYSTEMATIC REVIEW
Heat Acclimation Decay and Re-Induction: A Systematic Reviewand Meta-Analysis
Hein A. M. Daanen1 • Sebastien Racinais2 • Julien D. Periard2,3
Published online: 11 November 2017! The Author(s) 2017. This article is an open access publication
AbstractBackground Although the acquisition of heat acclimation
(HA) is well-documented, less is known about HA decay
(HAD) and heat re-acclimation (HRA). The available lit-erature suggests 1 day of HA is lost following 2 days of
HAD. Understanding this relationship has the potential to
impact upon the manner in which athletes prepare formajor competitions, as a HA regimen may be disruptive
during final preparations (i.e., taper).
Objective The aim of this systematic review and meta-analysis was to determine the rate of HAD and HRA in
three of the main physiological adaptations occurring
during HA: heart rate (HR), core temperature (Tc), andsweat rate (SR).
Data Sources Data for this systematic review were
retrieved from Scopus and critical review of the citedreferences.
Study Selection Studies were included when they met the
following criteria: HA, HAD, and HRA (when available)were quantified in terms of exposure and duration. HA had
to be for at least 5 days and HAD for at least 7 days forlongitudinal studies. HR, Tc, or SR had to be monitored in
human participants.
Study Appraisal The level of bias in each study wasassessed using the McMaster critical review form. Multiple
linear regression techniques were used to determine the
dependency of HAD in HR, Tc, and SR from the number ofHA and HAD days, daily HA exposure duration, and
intensity.
Results Twelve studies met the criteria and were system-atically reviewed. HAD was quantified as a percentage
change relative to HA (0% = HA, 100% = unacclimated
state). Adaptations in end-exercise HR decreased by 2.3%(P\0.001) for every day of HAD. For end-exercise Tc, the
daily decrease was 2.6% (P\0.01). The adaptations in Tcduring the HA period were more sustainable when the dailyheat exposure duration was increased and heat exposure
intensity decreased. The decay in SR was not related to the
number of decay days. However, protracted HA-regimensseem to induce longer-lasting adaptations in SR. High heat
exposure intensities during HA seem to evoke more sus-
tained adaptations in SR than lower heat stress. Only eightstudies investigated HRA. HRA was 8–12 times faster than
HAD at inducing adaptations in HR and Tc, but no dif-ferences could be established for SR.
Limitations The available studies lacked standardization in
the protocols for HA and HAD.Conclusions HAD and HRA differ considerably between
physiological systems. Five or more HA days are sufficient
to cause adaptations in HR and Tc; however, extending thedaily heat exposure duration enhances Tc adaptations. For
every decay day, * 2.5% of the adaptations in HR and Tcare lost. For SR, longer HA periods are related to betteradaptations. High heat exposure intensities seem beneficial
for adaptations in SR, but not in Tc. HRA induces adap-
tations in HR and Tc at a faster rate than HA. HRA maythus provide a practical and less disruptive means of
maintaining and optimizing HA prior to competition.
& Hein A. M. [email protected]
1 Department of Human Movement Sciences, Faculty ofBehavioural and Movement Sciences, Amsterdam MovementSciences, Vrije Universiteit Amsterdam, Van derBoechorststraat 7, 1081BT Amsterdam, The Netherlands
2 Athlete Health and Performance Research Centre, AspetarOrthopaedic and Sports Medicine Hospital, Doha, Qatar
3 Research Institute for Sport and Exercise, University ofCanberra, Canberra, ACT, Australia
123
Sports Med (2018) 48:409–430
https://doi.org/10.1007/s40279-017-0808-x
ACCLIMATIZATION, DECAY AND REACCLIMATIZATION: HEART RATE
ACCLIMATIZATION, DECAY AND REACCLIMATIZATION: CORE TEMPERATURE
DECAY OF ACCLIMATIZATION
• Foreverydecayday,≈2.5%ofadaptationsinheartrateandcoretemperaturearelost.
• Rateofdecayincoretemperaturecanbereducedwithincreaseddurationanddecreasedexposure.
SYSTEMATIC REVIEW
Heat Acclimation Decay and Re-Induction: A Systematic Reviewand Meta-Analysis
Hein A. M. Daanen1 • Sebastien Racinais2 • Julien D. Periard2,3
Published online: 11 November 2017! The Author(s) 2017. This article is an open access publication
AbstractBackground Although the acquisition of heat acclimation
(HA) is well-documented, less is known about HA decay
(HAD) and heat re-acclimation (HRA). The available lit-erature suggests 1 day of HA is lost following 2 days of
HAD. Understanding this relationship has the potential to
impact upon the manner in which athletes prepare formajor competitions, as a HA regimen may be disruptive
during final preparations (i.e., taper).
Objective The aim of this systematic review and meta-analysis was to determine the rate of HAD and HRA in
three of the main physiological adaptations occurring
during HA: heart rate (HR), core temperature (Tc), andsweat rate (SR).
Data Sources Data for this systematic review were
retrieved from Scopus and critical review of the citedreferences.
Study Selection Studies were included when they met the
following criteria: HA, HAD, and HRA (when available)were quantified in terms of exposure and duration. HA had
to be for at least 5 days and HAD for at least 7 days forlongitudinal studies. HR, Tc, or SR had to be monitored in
human participants.
Study Appraisal The level of bias in each study wasassessed using the McMaster critical review form. Multiple
linear regression techniques were used to determine the
dependency of HAD in HR, Tc, and SR from the number ofHA and HAD days, daily HA exposure duration, and
intensity.
Results Twelve studies met the criteria and were system-atically reviewed. HAD was quantified as a percentage
change relative to HA (0% = HA, 100% = unacclimated
state). Adaptations in end-exercise HR decreased by 2.3%(P\0.001) for every day of HAD. For end-exercise Tc, the
daily decrease was 2.6% (P\0.01). The adaptations in Tcduring the HA period were more sustainable when the dailyheat exposure duration was increased and heat exposure
intensity decreased. The decay in SR was not related to the
number of decay days. However, protracted HA-regimensseem to induce longer-lasting adaptations in SR. High heat
exposure intensities during HA seem to evoke more sus-
tained adaptations in SR than lower heat stress. Only eightstudies investigated HRA. HRA was 8–12 times faster than
HAD at inducing adaptations in HR and Tc, but no dif-ferences could be established for SR.
Limitations The available studies lacked standardization in
the protocols for HA and HAD.Conclusions HAD and HRA differ considerably between
physiological systems. Five or more HA days are sufficient
to cause adaptations in HR and Tc; however, extending thedaily heat exposure duration enhances Tc adaptations. For
every decay day, * 2.5% of the adaptations in HR and Tcare lost. For SR, longer HA periods are related to betteradaptations. High heat exposure intensities seem beneficial
for adaptations in SR, but not in Tc. HRA induces adap-
tations in HR and Tc at a faster rate than HA. HRA maythus provide a practical and less disruptive means of
maintaining and optimizing HA prior to competition.
& Hein A. M. [email protected]
1 Department of Human Movement Sciences, Faculty ofBehavioural and Movement Sciences, Amsterdam MovementSciences, Vrije Universiteit Amsterdam, Van derBoechorststraat 7, 1081BT Amsterdam, The Netherlands
2 Athlete Health and Performance Research Centre, AspetarOrthopaedic and Sports Medicine Hospital, Doha, Qatar
3 Research Institute for Sport and Exercise, University ofCanberra, Canberra, ACT, Australia
123
Sports Med (2018) 48:409–430
https://doi.org/10.1007/s40279-017-0808-x
RE-ACCLIMATIZATION TO HEAT
• OSHA:– 5daysafter2weeksaway
• MSHA:– 4daysafter8daysaway;Beginningwith50%
• NIOSH– 4daysbeginwith50%
RE-ACCLIMATIZATION TO HEAT
• Research:– 4daysafter2weeksaway– 5daysafter4weeksaway
PROPOSED HEAT ACCLIMATIZATION TABLES
• Heatstressisbasedon:– Environmentalconditions– Metabolicrate– Clothing
ACCLIMATIZATION GUIDELINES ACCORDING TO TEMPERATURE AND WORK RATE
RecommendationsforHeatAcclimatizationforWarmConditions LightWork(125-275W) ModerateWork(275-375W) Hard Work (375 - 475 W)
TimeSpent
workinginhotenvironment
HeatAcclimatization
Days
TimeSpentworkinginhotenvironment
HeatAcclimatization
DaysTimeSpentworkinginhotenvironment
HeatAcclimatization
DaysWBGT℉78-81.9 90-100% 2 - 3 70-100% 3 - 5 50-100% 682-84.9 80-100% 2 - 4 70-100% 3 - 5 50-100% 685-87.9 70-100% 3 - 5 60-100% 4 - 6 50-100% 688-89.9 60-100% 4 - 6 50-100% 6 50-100% 690+ 50-100% 6 50-100% 6 50-100% 6
RE-ACCLIMATIZATION GUIDELINES ACCORDING TO TEMPERATURE AND WORK RATE
RecommendationsforRe-AcclimatizationforWarmConditionsRoutineAbsence AbsenceDue
toIllness
GREEN
Day1 Day2 Day3 Day4 Day5< 4 -- 100 4-5 1-3 90 100 6-12 4-5 80 90 100 12-20 6-8 60 80 90 100
>20 >8 50 60 80 90 100
RoutineAbsence AbsenceDue
toIllness
YELLOW
Day1 Day2 Day3 Day4 Day5< 4 -- 90 100 4-5 1-3 80 90 100 6-12 4-5 70 80 90 100 12-20 6-8 60 70 80 90 100
>20 >8 50 60 70 80 90
RoutineAbsence AbsenceDue
toIllness
RED
Day1 Day2 Day3 Day4 Day5< 4 -- 80 90 100 4-5 1-3 60 80 90 100 6-12 4-5 50 60 80 90 10012-20 6-8 50 60 70 80 90
>20 >8 50 60 70 80 90
CONCLUSION
• Establishingheatacclimatizationpoliciesiscrucialinensuringworkersafety.
• Adaptationsofacclimatizationcanbeaccruedin5to6dayswithgreaterbenefitswithlongerexposures.
• Acclimatizationislostwhenworkersareawayfromtheheat,andare-acclimatizationscheduleiswarranted.
• Prudentacclimatizationandreacclimatizationguidelinesshouldtakeintoaccountenvironmentalconditionsandworkrate.
THANK YOU FOR YOUR TIME!