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Stroke volume during exercise: interaction of environment and hydration
J González-Alonso1, R Mora-Rodríguez, E F Coyle
1Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas, Austin, Texas 78712, USA. jga@cmrc.dk
American Journal of Physiology. Heart and Circulatory Physiology
|February 9, 2000
Summary
Dehydration significantly reduces stroke volume (SV) during exercise in both heat and cold, primarily due to increased heart rate and reduced blood volume, not skin blood flow.
Area of Science:
- Exercise Physiology
- Environmental Physiology
- Cardiovascular Regulation
Background:
- Stroke volume (SV) regulation during exercise is complex, influenced by hydration status and environmental temperature.
- Understanding factors affecting SV is crucial for optimizing athletic performance and safety.
Purpose of the Study:
- To investigate the relationship between hydration status, environmental temperature, and stroke volume during endurance exercise.
- To determine whether elevated skin blood flow or other factors are primarily responsible for reduced SV in heat.
Main Methods:
- Eight endurance-trained male cyclists performed 30-minute cycling bouts at 72% VO2 max in hot (35°C) and cold (8°C) conditions.
- Subjects were tested euhydrated and dehydrated to 1.5%, 3.0%, and 4.2% body weight loss.
- Measurements included stroke volume, esophageal temperature, heart rate, and skin blood flow.
Main Results:
- When euhydrated, SV and esophageal temperature were similar in hot and cold conditions, despite higher skin blood flow in the heat.
- Each 1% body weight loss reduced SV by 4.8% in heat and 2.5% in cold.
- Reduced SV was strongly associated with increased heart rate and decreased blood volume in both environments, not skin blood flow.
Conclusions:
- Stroke volume is maintained in trained individuals during exercise in euhydrated states, irrespective of significant differences in skin blood flow between hot and cold environments.
- Dehydration significantly lowers stroke volume during exercise, an effect primarily driven by compensatory increases in heart rate and reductions in blood volume.