🏜️ What Is Dehydration?
Dehydration is a state in which fluid loss exceeds intake. In sport, dehydration occurs mainly due to sweating, but also through water vapor during breathing. Even a 2% loss of body mass through sweat can significantly reduce physical capacity — especially in endurance sports and in hot environments.
📊 Degrees of Dehydration and Effects
| Fluid Loss (% of Body Mass) | Physiological Effect | Effect on Performance |
|---|---|---|
| 1-2% | Reduced blood plasma volume, heart rate begins to rise | Slight reduction in endurance, increased perceived exertion |
| 2-3% | Reduced cardiac output, rising body temperature | Significant reduction in endurance, reduced concentration |
| 3-4% | Markedly reduced blood volume, high cardiac strain | Drastic drop in performance (15-30%), dizziness |
| 4-5% | Thermoregulation impairment, electrolyte imbalance | Serious risk of heat stroke and collapse |
| >5% | Critical organ function impairment | Life-threatening — emergency medical help required |
🧬 Physiological Mechanisms
🫀 Cardiovascular System
Reduced blood plasma volume lowers cardiac output. Heart rate must rise to compensate — greater cardiac work for the same load.
🌡️ Thermoregulation
Less fluid = less sweat = less cooling. Body temperature rises faster, which suppresses the central nervous system.
🧠 Central Nervous System
Dehydration affects the CNS — concentration, reaction time, and decision-making speed decrease. This is critical in technical sports.
💪 Muscle Function
Electrolyte imbalance disrupts muscle contraction — the risk of cramps increases. The ability to generate force decreases.
📋 How to Assess Hydration Status?
- Urine color: Pale yellow (straw-colored) = well hydrated. Dark yellow or brown = dehydrated. Use the urine color scale (1-8). Morning urine is the most informative.
- Body mass change: Weighing before and after training. A 1 kg weight loss = ~1 L fluid loss. Replenish 1.25-1.5 L for each lost kg.
- Thirst sensation: Unreliable — when we feel thirsty, we are already 1-2% dehydrated. Athletes should drink according to a plan, not only according to thirst.
- Urine specific gravity (USG): An indicator measured with a refractometer. USG <1.020 = gerai hidratuotas, >1.030 = dehydrated.
🎯 Rehydration Strategy
Effective rehydration requires more than just water. After intense training, both fluids and electrolytes need to be restored.
⏱️ Timing
Drink immediately after exertion. The first 2 hours are a critical window. Continue over 4-6 hours after exertion. Do not drink everything at once — take small sips every 15-20 min.
⚡ Electrolytes
Water + electrolytes (especially sodium) = more effective rehydration. Sodium helps retain fluids in the body and stimulates thirst. Sports drinks with 20-50 mmol/L Na+.
🍽️ Food
Salty food after training helps retain fluids. Along with fluids, consume lightly salted food — soup, nuts, cheese.
🧪 Individual Plan
Calculate your sweating rate: (weight before - weight after + fluids consumed) / time in hours. Know your numbers!
🙋 Frequently Asked Questions
Yes! Understanding the effects of dehydration on sport helps you train more effectively, avoid injuries, and achieve better results even at amateur level.
We recommend PubMed, Google Scholar, and Sports Medicine journals. It is also worth following publications from the Lithuanian Sports University.
It depends on the specific study. Some methods require laboratory equipment, while others can be performed with portable devices.
Coaches who understand the effects of dehydration on sport can individualize training programs, monitor progress, and adjust loads in a timely manner.
📚 Additional Resources and Sources
To deepen your knowledge about the effects of dehydration on sport, we recommend:
- Scientific publications and conferences of the Lithuanian Sports University (LSU)
- International journals: Journal of Sports Sciences, Medicine and Science in Sports and Exercise
- Annual congresses of the European College of Sport Science (ECSS)
- Sports science podcasts: Science of Sport, The Real Science of Sport
- Sports science programs of the Lithuanian National Olympic Committee (LTOK)
⚡ Pro Tip
Sports science is constantly evolving. What was considered true 10 years ago may be refuted today by new research. Be curious, read the latest literature, and don't be afraid to experiment — of course, while following safety principles.