Fluid and electrolytes

Water is the largest component of the body, comprising 45–75% of body weight.
Functions of water:
- Lubrication (joints, tissues)
- Shock absorption (brain, spinal cord)
- Body temperature regulation (cooling via sweat)
- Nutrient transport and waste removal
- Blood pressure maintenance
The body cannot survive more than a few days without water.

Fluid balance in athletes

Daily fluid intake recommendations (AI):
- Men: 3.7 L (125.1 oz)
- Women: 2.7 L (91.3 oz)
- Pregnant women: 3.0 L
- Lactating women: 3.8 L
Athletes may require more fluids, depending on:
- Sweat rate
- Environmental conditions (heat, humidity, altitude)
- Clothing and equipment
Sweat loss and dehydration risk:
- Linemen in football experience high sweat rates due to heavy gear.
- Basketball players lose around 1.6–3.5 L (54.1–118.4 oz) per game.

Dehydration risks:
- >2% body weight loss from sweat impairs performance.
- Symptoms include increased core temperature, heart rate, and perceived exertion.
Assessing hydration status:
- Urine specific gravity (USG) and plasma osmolality are effective measures.
- Urine color is not always reliable due to vitamin and food influences.

Biomarkers of hydration status

Measure	Practicality	Validity (acute vs. chronic changes)	EUH Cutoff
Total body water	Low	Acute and chronic	<2%
Plasma osmolality	Medium	Acute and chronic	<290 mOsmol
Urine specific gravity	High	Chronic	<1.020 g/ml
Urine osmolality	High	Chronic	<700 mOsmol
Body weight	High	Acute and chronic	<1%

Electrolytes lost in sweat:
- Sodium chloride (NaCl) – Most significant loss
- Potassium, magnesium, calcium – Minor losses
Sodium functions:
- Helps retain fluid and prevent cramping.
- Sodium losses in sweat vary from 0.2 to 12.5 g/L.
Athletes should replace sodium losses:
- Salty snacks, sports drinks, and broth-based soups can help.
Hyponatremia (low sodium levels):
- Occurs when excess water dilutes sodium levels below 130 mmol/L.
- Can lead to seizures, brain swelling, and death.

Before training:
- Prehydrate several hours before exercise.
- Ensure USG <1.020 (indicating hydration).
During training:
- Children (40 kg/88 lbs): Drink 150 mL (5 oz) every 20 minutes.
- Adolescents (60 kg/132 lbs): Drink 250 mL (9 oz) every 20 minutes.
- Adults: Use individualized hydration plans.
- During prolonged activity, consume 460–690 mg sodium/L, 78–195 mg potassium/L, and 5–10% carbohydrate solutions.
After training:
- Replace fluid and electrolytes lost.
- Consume 1.5 L (50 oz) per kg of body weight lost.
- If fluid loss is >2% of body weight, increase sodium intake.