Related Experiment Video
Updated: Jun 29, 2026
08:22
Using an Ingestible Telemetric Temperature Pill to Assess Gastrointestinal Temperature During Exercise
Published on: October 7, 2015
Thermoregulatory responses to constant versus variable-intensity exercise in the heat
Ricardo Mora-Rodriguez1, Juan Del Coso, Emma Estevez
1University of Castilla-La Mancha, Exercise Physiology Laboratory at Toledo, Spain. Ricardo.Mora@uclm.es
Medicine and Science in Sports and Exercise
|October 11, 2008
Summary
Variable-intensity exercise in heat increases physiological stress, including higher heat storage and dehydration, compared to constant-intensity exercise. This makes variable-intensity exercise less optimal for minimizing physiological strain during prolonged activity.
Area of Science:
- Exercise Physiology
- Environmental Physiology
- Thermoregulation
Background:
- Understanding thermoregulatory responses during exercise in hot environments is crucial for athlete safety and performance.
- Heat acclimatization and exercise intensity significantly influence physiological strain.
Purpose of the Study:
- To compare thermoregulatory responses between constant-intensity exercise (CON) and variable-intensity exercise (VAR) in a dry-hot environment.
- To evaluate the impact of exercise intensity patterns on physiological stress markers.
Main Methods:
- Seven heat-acclimated, endurance-trained subjects performed 90-minute cycling trials at identical total work output.
- Exercise protocols included constant 60% VO2max (CON) and alternating 1.5 min at 90% VO2max with 4.5 min at 50% VO2max (VAR).
Main Results:
- Variable-intensity exercise (VAR) resulted in significantly higher heat storage, increased rectal temperature, and elevated heart rate compared to constant-intensity exercise (CON).
- VAR also led to lower forearm skin blood flow, higher sweat rates, greater dehydration, and increased blood lactate levels.
- Net metabolic heat production was not significantly different between the two exercise conditions.
Conclusions:
- Ninety minutes of variable-intensity exercise in a hot environment exacerbates physiological stress, including thermal, cardiovascular, and metabolic strain, compared to constant-load exercise.
- Variable-intensity exercise leads to increased heat storage and fluid deficit.
- Constant-intensity exercise is more advisable than variable-intensity exercise when the primary goal is to minimize physiological stress in hot conditions.
Related Concept Videos
02:45Responses to Heat and Cold Stress
Every organism has an optimum temperature range within which healthy growth and physiological functioning can occur. At the ends of this range, there will be a minimum and maximum temperature that interrupt biological processes.
01:26Thermoregulation
The human body has a sophisticated thermoregulation system that employs negative feedback mechanisms to maintain an optimal core temperature. When the core temperature drops, peripheral and central thermoreceptors send signals to the hypothalamus, activating the heat-promoting center. This center triggers several responses aimed at increasing the core temperature. First, vasoconstriction reduces the flow of warm blood from internal organs to the skin so that the heat is not lost from the skin,...
01:20Exercise and Cardiovascular Response
Exercise significantly impacts cardiovascular response, which is crucial for understanding patient health and designing effective treatment plans.
Light to moderate physical activity initiates a series of interconnected responses in the body. The heart rate modestly increases in anticipation of the workout, followed by widespread vasodilation as oxygen consumption by skeletal muscles increases. This results in decreased peripheral resistance, increased capillary blood flow, and accelerated...
Light to moderate physical activity initiates a series of interconnected responses in the body. The heart rate modestly increases in anticipation of the workout, followed by widespread vasodilation as oxygen consumption by skeletal muscles increases. This results in decreased peripheral resistance, increased capillary blood flow, and accelerated...
01:25Body Temperature
The body's temperature, measured in degrees, is determined by the balance between heat production and dissipation to the surrounding environment. For instance, if exercising vigorously, the body will produce more heat, causing sweat and dissipating that heat. Despite extreme environmental conditions and physical exertion, the human temperature-control system maintains a constant core body temperature (the temperature of deep tissues, which are the tissues located beneath the skin and other...
01:07Body Temperature
Body temperature reflects the equilibrium between heat production and heat loss within the body. Most heat is generated by metabolically active tissues, particularly the liver, heart, brain, kidneys, and endocrine organs. At rest, skeletal muscles contribute 20–30% of total heat production, but during vigorous exercise, this can increase up to 30–40 times.
The average body temperature is approximately 37°C (98.6°F) and typically ranges from 36.1–37.2°C (97–99°F), remaining relatively stable...
The average body temperature is approximately 37°C (98.6°F) and typically ranges from 36.1–37.2°C (97–99°F), remaining relatively stable...
01:26Requirements for Human Life
The Earth and its atmosphere have provided humans with air, water, and food, but these are not the only requirements for survival. Humans also require a specific range of temperature and pressure that the Earth and its atmosphere provides.
Oxygen
Atmospheric air is only about 20 percent oxygen, but that oxygen is a key component of the chemical reactions that keep the body alive, including the reactions that produce ATP. Brain cells are susceptible to a lack of oxygen because they require a...
Oxygen
Atmospheric air is only about 20 percent oxygen, but that oxygen is a key component of the chemical reactions that keep the body alive, including the reactions that produce ATP. Brain cells are susceptible to a lack of oxygen because they require a...