Exercise in Extreme Hot Weather Conditions (EXHOTCON)

Physiological Responses in Semi-professional Athletes: a Comparison of the Effects of Hot Weather Conditions

Background: Core body temperature increases in hot climates due to exercise workload, disrupting heat gain and loss of balance. The human thermoregulatory system regulates core body temperature through factors such as metabolic heat production, air temperature, humidity, and clothing. The study investigates physiological thermoregulatory responses in semiprofessional athletes during walking and jogging in different climatic conditions.

Methods: A factorial experimental interventional design was used to evaluate different physical activity (low (L)=5 km/h and high (H)=8 km/h) and climatic conditions within the Thermal Environment Laboratory at Lund University, Sweden. The temperature within the climatic chamber was set at 40°C and 31°C, with a relative humidity of 20% and 70%, (hot dry (HD) and hot humid (HW), respectively, to account for a 28°C WBGT. The study used independent T-tests, ANOVA and simple linear regression models to analyse the physiological responses of semiprofessional athletes under different test conditions, comparing gender differences.

Study Overview

• Status: Completed
• Conditions: Heat Acclimation and Thermotolerance; Heat Effect
• Intervention / Treatment: Other: hot wet high (HWH); Other: hot dry high (HDH); Other: Experimental: hot dry low (HWL); Other: Experimental: hot wet low (HWL)

• Study Type: Interventional
• Enrollment (Actual): 6
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Spain
  • Soria
    • Soria, Soria, Spain, 42004
      • Faculty of Health Sciences, University of Valladolid Soria Campus, Soria, Soria 42004

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Participation at the regional competition level
• Receiving monetary remuneration for their sports engagement
• Participating in sports activities in the previous six years
• Average training experience of 6.0±1.4 years
• A weekly volume of 6.3±0.7 days for 2.3±0.7 hours (h)·day-¹.

Exclusion Criteria:

• A 2 kg weight change in the previous month
• Adherence to special diets
• Use of nutritional supplements
• Smoking
• An acute or chronic communicable or noncommunicable disease
• Heat allergic problems.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: hot wet high (HWH); Air Temperature (ºC) 30.6±1.2 Relative Humidity (%) 68.6±1.3 Vapour Pressure (kPa) 1011±1.1 Bruel and Kjear (WBGT ºC) 27.3±0.8 Heat Stress (WBGT ºC) 27.8±0.8 Air Velocity (m/s) 0.45±0.19	Other: hot wet high (HWH); Air Temperature (ºC) 30.6±1.2 Relative Humidity (%) 68.6±1.3 Vapour Pressure (kPa) 1011±1.1 Bruel and Kjear (WBGT ºC) 27.3±0.8 Heat Stress (WBGT ºC) 27.8±0.8 Air Velocity (m/s) 0.45±0.19
Experimental: hot dry high (HDH); Relative Humidity (%) 39.7±0.3 Vapor Pressure (kPa) 29.0±1.2 Bruel and Kjear (WBGT ºC) 1007.9± 6.4 Heat Stress (WBGT ºC) 28.9±0.6 Air Velocity (m/s) 28.4±0.3	Other: hot dry high (HDH); Relative Humidity (%) 39.7±0.3 Vapor Pressure (kPa) 29.0±1.2 Bruel and Kjear (WBGT ºC) 1007.9± 6.4 Heat Stress (WBGT ºC) 28.9±0.6 Air Velocity (m/s) 28.4±0.3
Experimental: hot dry low (HWL); Relative Humidity (%) 31.1±0.1 Vapor Pressure (kPa )67.1±1.0 Bruel and Kjear (WBGT ºC)1005.7±8.0 Heat Stress (WBGT ºC) 27.4±0.6 Air Velocity (m/s) 27.9±0.3	Other: Experimental: hot dry low (HWL); Relative Humidity (%) 31.1±0.1 Vapor Pressure (kPa )67.1±1.0 Bruel and Kjear (WBGT ºC)1005.7±8.0 Heat Stress (WBGT ºC) 27.4±0.6 Air Velocity (m/s) 27.9±0.3
Experimental: hot wet low (HWL); Relative Humidity (%) 39.8±0.1 Vapor Pressure (kPa) 26.4±0.4 Bruel and Kjear (WBGT ºC) 1004.7±10.7 Heat Stress (WBGT ºC) 28.3±0.3 Air Velocity (m/s) 27.7±0.1	Other: Experimental: hot wet low (HWL); Relative Humidity (%) 39.8±0.1 Vapor Pressure (kPa) 26.4±0.4 Bruel and Kjear (WBGT ºC) 1004.7±10.7 Heat Stress (WBGT ºC) 28.3±0.3 Air Velocity (m/s) 27.7±0.1

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Exposure Time	duration an athlete is exposed to a specific intensity or environmental condition	Just one day, the day of the test, in those weather conditions
Heart Rate	measures how hard your heart works to gauge fitness	Just one day, the day of the test, in those weather conditions
Oxygen Uptake	how much oxygen your body uses during activity	Just one day, the day of the test, in those weather conditions

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Core Body Temperature	the body's internal temperature regulation	Just one day, the day of the test, in those weather conditions
Skin Temperature	The temperature of your body's surface	Just one day, the day of the test, in those weather conditions
Body Temperature	the internal heat level of the human body	Just one day, the day of the test, in those weather conditions
Sweat Rate	the amount of fluid your body loses through sweat per hour during exercise	Just one day, the day of the test, in those weather conditions
Perceived Exertion Level	is a subjective scale that measures how hard your body feels it's working during exercise	Just one day, the day of the test, in those weather conditions
Thermal Sensation Level	The Thermal Sensation Level is a standardized, subjective rating system used to quantify a person's perception of warmth or coolness in their environment	Just one day, the day of the test, in those weather conditions

Collaborators and Investigators

• Sponsor: University of Valladolid

Study record dates

Study Major Dates

• Study Start (Actual): July 7, 2025
• Primary Completion (Actual): December 10, 2025
• Study Completion (Actual): December 12, 2025

Study Registration Dates

• First Submitted: December 14, 2025
• First Submitted That Met QC Criteria: December 14, 2025
• First Posted (Estimated): December 29, 2025

Study Record Updates

• Last Update Posted (Actual): December 31, 2025
• Last Update Submitted That Met QC Criteria: December 26, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Keywords: Gender difference; Heat Stress; WBGT; Exposure time
• Additional Relevant MeSH Terms: Wounds and Injuries; Heat Stress Disorders
• Other Study ID Numbers: 2025.14.11

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No