Theses and Dissertations

ORCID

https://orcid.org/0000-0002-0552-5450

Advisor

Smith, JohnEric

Committee Member

Ruby, Brent

Committee Member

Gillen, Zachary

Committee Member

Knight, Adam

Date of Degree

5-15-2026

Original embargo terms

Immediate Worldwide Access

Document Type

Dissertation - Open Access

Major

Kinesiology (Exercise Science)

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Education

Department

Department of Kinesiology

Abstract

The agricultural community in Mississippi is critical to the state’s economy and the health of its communities. Farm workers meet these needs by performing highly demanding work with long hours of labor, limited resources, and stressful environmental conditions. The purpose of this investigation was to examine and measure indicators of physiological and behavioral adaptations to the heat such as whole body sweat rate (WBSR), sweat sodium (Na+) content, urine specific gravity (USG), and fluid intake, as well as determine total daily energy expenditure (TEE) and water influx (rH2O) via the doubly labeled water technique (DLW) in farm workers during the summer harvest season Mississippi. Twenty-four farm workers (12 male, 12 female) were assessed during work in field conditions in various locations in Mississippi during August and September. To measure WBSR, sweat Na+, USG, and fluid intake, researchers spent one day assessing all workers from the start of their workday until completion of all outdoor work. Wet bulb globe thermometry (WBGT) was used to assess environmental conditions during work. Six of these participants also ingested a dose of DLW the night before beginning their work week and TEE and rH2O were derived from isotopic elimination rates. WBGT data indicated high levels of environmental heat stress in all locations. Start of day USG was significantly lower than end of day USG, and WBSR and sweat Na+ values indicated high levels of heat acclimatization. Males and females demonstrated similar values in all metrics except WBSR, TEE, and body composition metrics derived from isotopic elimination. Body mass of DLW participants remained stable throughout the work period, and TEE and rH2O were high compared to values seen in other occupational populations. SR was similar to others working in other outdoor manual labor jobs in similar conditions and Na+ loss was moderately high, and fluid loss and USG values show that these workers do not adequately replace sweat losses. Despite stressful working conditions, workers demonstrated levels of heat acclimatization and energy and fluid balance that allowed them to sustain demanding work throughout a typical summer work week.

Sponsorship (Optional)

Acknowledgement: “This research was conducted using the Isotope Ratio Mass Spectrometry Laboratory at the Biotechnology Center of the University of Wisconsin–Madison, supported by the Shared Instrumentation Grant Program of the National Institutes of Health under award number 1S10OD036349-01. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.”

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