Hydration Differences

Hydration Differences

It is well known that dehydration can impair performance and that being dehydrated by as little as 2% of body mass cause early fatigue and impair their ability to regulate body temperature. For swimmers, even thou they are in water and you cannot see the sweat, it is just as important to drink adequate fluids in maintaining coordination, concentration and ensuring that recovery is optimized. 

Although most swimmers and coaches are aware of the importance of hydration, recent data collected shows that changes in body composition and hydration status are different in male compared to female open-water ultra-endurance swimmers.

Researchers from the Institute of General Practice and for Health Services Research, University of Zurich , Switzerland, investigated body mass changes during ultra-endurance performances of swimming in a heated pool. The field study of involved 20 male and 11 female open-water swimmers and investigated the changes in body composition and hydration status during an ultra-endurance event. Body mass, both estimated fat mass and skeletal muscle mass, haematocrit, plasma sodium concentration ([Na(+)]) and urine specific gravity were determined. Energy intake, energy expenditure and fluid intake were estimated.

Males experienced significant reductions in body mass (-0.5 %) and skeletal muscle mass (-1.1 %) (P < 0.05) during the race compared to females who showed no significant changes with regard to these variables (P > 0.05). Changes in percent body fat, fat mass, and fat-free mass were heterogeneous and did not reach statistical significance (P > 0.05) between gender groups. Fluid intake relative to plasma volume was higher in females than in males during the ultra-endurance event. Compared to males, females' average increase in haematocrit was 3.3 percentage points (pp) higher, urine specific gravity decrease 0.1 pp smaller, and plasma [Na(+)] 1.3 pp higher.

The observed patterns of fluid intake, changes in plasma volume, urine specific gravity, and plasma [Na(+)] suggest that, particularly in females, a combination of fluid shift from blood vessels to interstitial tissue, facilitated by skeletal muscle damage, as well as exercise-associated hyponatremia had occurred. To summarise, changes in body composition and hydration status are different in male compared to female open-water ultra-endurance swimmers.

Some helpful hydration tips;

1. Hydration Before Exercise

• Most individuals dehydrate overnight by at least 1 litre. Keep a water bottle at bedside for easy access to fluid during the night. Upon waking consume several glasses of water.

• Be organized. Always carry a drink bottle and sip water regularly during the day. Drink at least 2 litres a day during non training times.

• Drink 250-500 mL of water 20-45 minutes before exercise.

2. Hydration During Exercise

• Practice drinking during training and aim to maintain body weight.  For example, if you lose 1 kg during training that equates to approximately 1 L of fluid and you should be aiming to drink at least 1000 ml.

• For long swimming sessions a carbohydrate-electrolyte drink will provide both fluid and energy. As a general guide, ingest 200-250 mL of 5-7% carbohydrate drink every 15-20 minutes (up to ~60g carbohydrate/hour). In very hot conditions, diluting a sports drink by 15-20% may enhance fluid absorption.

• Drink iccy cold fluids that you like. Fluids that taste good at rest may not taste so good while exercising, therefore it is recommended that you try different flavours and concentrations.

3. Hydration After Exercise

• Replace fluids, carbohydrate and sodium, magnesium lost during exercise to minimize dehydration, to stabilize blood volume, and to avoid muscle cramps. Carbohydrate and sodium is best replaced through food intake!

• Checking hydration status by monitoring urine output. It should be clear or pale yellow and produced in sufficient volume.