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Hydration and Blood Plasma Volume

Hydration in tennis is not simply about drinking water — it is about maintaining blood plasma volume and electrolyte homeostasis. A 2% loss of body weight through sweat produces a measurable drop in metabolic efficiency and hitting accuracy. A 3–5% loss begins to accelerate the Performance Cliff.

The Physiology

Tennis athletes are heavy sweaters, losing 1.0–2.5 litres of fluid per hour in hot conditions. As fluid is lost:

Cardiovascular Drift: Blood becomes more viscous (thicker). The heart must beat faster to maintain oxygen delivery to the kinetic chain, causing premature aerobic fatigue. The aerobic system's role — recharging the anaerobic ATP-PC system between points — becomes less efficient, shortening the explosive sprint battery's recovery window.

Thermoregulation Failure: Reduced blood volume means less blood reaches the skin for cooling. Core temperature rises, accelerating neuromuscular fatigue — the cognitive dimension of the Performance Cliff manifests earlier under heat stress.

Electrolytes: Not Just Water

Sweat is a saline solution containing vital minerals:

Sodium (Na⁺): The most critical. Sodium maintains the thirst drive and holds water in the bloodstream. Drinking plain water without sodium replacement can dilute blood sodium to dangerous levels (Hyponatremia), a risk for players who drink very large volumes of plain water on hot days.

Potassium and Magnesium: These minerals facilitate the electrical signals that cause muscles to contract. A deficit is a primary cause of exercise-associated muscle cramping — the "dead legs" sensation in late sets.

Match-Day Protocol

Pre-hydration (2 hours before): 500–700ml of water with an electrolyte tablet. Starting with a "full tank" prevents early cardiovascular drift.

On-court (every changeover): 150–250ml of a 6–8% carbohydrate-electrolyte solution. The carbohydrates assist water absorption in the small intestine and provide a glucose top-up.

The Weight Test: Weigh before and after a match. For every 1kg of weight lost, consume 1.5 litres of fluid to fully rehydrate. This 1.5:1 ratio accounts for ongoing urine losses during rehydration.

The Clear Goal

The simplest monitoring tool: urine colour.

Urine Colour Status Action
Pale straw / lemonade Optimal hydration Maintain current protocol
Dark yellow Early dehydration warning Increase intake at next changeover
Dark amber / apple juice Significant dehydration Immediate attention; heat stress risk

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