Graduation Year

2021

Document Type

Thesis

Degree

M.S.P.H.

Degree Name

MS in Public Health (M.S.P.H.)

Degree Granting Department

Public Health

Major Professor

Thomas E. Bernard, Ph.D.

Committee Member

Steven P. Mlynarek, Ph.D.

Committee Member

Rene' R. Salazar, Ph.D.

Keywords

hot/dry, warm/humid, physiologic, WBGT

Abstract

Heat acclimatization provides the opportunity to better tolerate heat stress. Different methods are used to acclimatize participants as part of heat stress studies in the laboratory. The usual acclimatization protocols are greater than the occupational exposure limit represented by the ACGIH TLV® and NIOSH REL. The purpose of this paper was to examine the acclimatization state prior to and at the end of a one-week acclimatization program using two acclimatization protocols.

Prior heat stress studies at the University of South Florida (USF) used two heat stress conditions for participants’ acclimatization. Participants (n = 43) were evaluated using four different studies consisting of two types of acclimatization protocols. Conditions for the protocols were designated as conditions 1 (CD1) (n = 35) and conditions 2 (CD2) (n = 8). CD1 environmental conditions were 500C, 20% rh (360C, WBGT) and those for CD2 were 400C, 30% rh (300C, WBGT). All acclimatization protocols involved walking on a motorized treadmill at a moderate work rate (300 W) for 2 hours. The reference TLV® was 28°C. Heart rate (HR) and rectal temperature (Tre) were measured. Trials lasted 120 minutes unless any of the termination criteria was reached: Tre = 390C, HR > 90% of maximum HR or participant wished to stop. Acclimatization status for the first and last day was determined by two experienced researchers based on Tre and HR.

On the first day, 14% of the participants were classified as acclimatized under the CD1 protocol. Three quarters of participants under CD2 were also classified as acclimatized on the first day. Full acclimatization was achieved in 34% of participants in CD1 protocol on the last day. Another 34% demonstrated some improvement and the remaining 31% showed no improvement in heat tolerance under the CD1 protocol. There was no change in acclimatization status for participants in the CD1 protocol on the last day, with 2 of the 8 showing no improvement. The harsher the condition, the harder it is to tolerate heat stress at the TLV and CD1 appeared to be more successful at acclimatizing participants than CD2.

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