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Friday, February 24th
10:00 AM

Fluid Balance Across the Menstrual Cycle During Exercise in the Heat

Katie S. Christison, University of Montana, Missoula
Shae C. Gurney, University of Montana, Missoula
Cassie M. Williamson-Reisdorph, University of Montana, Missoula
Anna C. Covington, University of Montana, Missoula

UC 332

10:00 AM - 10:15 AM

Background: Attenuating core temperature elevations is crucial for wildland firefighters during field operations. Fluid intake and retention is one component to address rises in core temperature. Female wildland firefighters (WLFF) might be challenged to maintain fluid balance due to hormonal fluctuations throughout their menstrual cycle. Long periods of exercise in the heat could alter fluid balance and core temperature and risk WLFF safety in the field. The purpose of this study is to examine the effect of uncompensable heat stress on eumenorrheic females across the two phases of the menstrual cycle.

Methods: In a crossover design, 12 females walked for two 180-minute trials in a heat chamber (35ºC and 30% relative humidity) during early follicular (FP) and mid luteal (LP) phases of their menstrual cycle. Following a 10-minute seated acclimation, subjects completed three 50-minutes intervals of exercise at 50% of their maximum aerobic capacity and 10 minutes of rest. Physiological strain index (PSI), core temperature (TCORE), skin temperature (TSKIN), and perceived heat (PH) were measured throughout both trials. Nude body weight (NBW), blood samples, and urine were collected pre- and post- trial. Blood samples were analyzed for aldosterone.

Results: Aldosterone was 34% higher at rest in the LP compared to FP at rest. After the 180-minute trial, aldosterone was elevated from baseline in both phases. Similarly, TCORE was 0.3 ºC higher in the LP at rest and rose similarly across the two phases. PSI and TSKIN increased throughout the exercise, peaking at 170 minutes in both LP and FP. Perceived heat showed a time*phase interaction. Sweat rate and percent dehydration were not different between the trials.

Significance: This study is the first to examine the impact of the menstrual cycle on fluid balance hormones during exercise. These data suggest that females exhibit thermoregulatory stress during prolonged exercise, exacerbated in the LP due to elevated basal core temperature. Despite this, increased fluid retention hormones (aldosterone) in the LP indicates a greater potential for combating dehydration. To further this point, subjects’ perceived heat was lower in this phase. This study provides an important step in identifying a previously unrecognized hormonal influence on fluid retention.

10:20 AM

Ambient temperature and injuries among Montana workers

MD Zahid Hasan, University of Montana, Missoula

UC 332

10:20 AM - 10:35 AM

Introduction: Several heat related risks increase the chance of injuries in workers. During a warmer season, workers may experience serious heat related illness as their internal body temperature is also affected by the high temperature outside. Heat related injuries and illness (such as heat exhaustion, heat stress, and heat stroke) can cause sudden death due to cardiac arrest or permanent body injuries. As a result of climate change, increasing opportunities for heat exposure may affect the working environments and risk of injury among workers.

Objective: To evaluate the connection between temperature on number of injuries in workers who claimed compensation due to workplace injuries using the worker compensation dataset from 2007 to 2022 in Montana.

Method: This research will be based on the worker compensation dataset from 2007 to 2022. Worker heat exposure will be assessed using the daily data from Gridded Surface Meteorological (gridMET) during the warm season. Specifically, we will use record of daily minimum temperature, maximum temperature, and average relative humidity of each Montana county during 2007 to 2022. We will employ a time-stratified case-crossover approach with conditional Poisson regression, comparing ambient temperature on the day of injury compared to ambient temperature on control days. Furthermore, we will assess whether the association between temperature and injuries of workers is linear or non-linear.

Originality: Previously, no study has explored the association between meteorological conditions, specifically temperature humidity, and frequency of injuries among Montana workers. Moreover, this study includes three workers group (firefighters, construction workers, and professional workers), allowing for assessment of how the associations vary according to general working conditional among these groups.

Significance: Understanding the risk of worker injury according to meteorological conditions will indicate the need for preventive measures than can be taken to minimize worker exposure to extreme heat conditions.