Hydration for Exercise
Hydration, on the surface, might sound like a simple topic, but so many of us aren't reaching an adequate hydration level regularly.
We lose water each day through our bodily functions. Water is lost via sweating, urinating and also through breathing as we lose water molecules as we exhale. The more active we are, the more likely we are to become dehydrated.
Our bodies inform us that we need hydration by making us feel thirst. You may notice you feel more thirsty after exercising, or on a hot day, making you reach for extra drinks. Pay attention to cues and ensure you are reaching for hydrating drinks such as water and teas as opposed to excessive sugary beverages and alcohol. As alcohol is a diuretic it causes increased urination, leading to dehydration, this is one of the reasons we feel a bit worse for wear the day after the night before!! Ensure you take a glass of water occasionally on your next big night out!
Proper hydration keeps the body healthy by eliminating toxins through the kidneys, preventing constipation, ensuring our electrolyte balance in optimal, increased heart rate as our blood plasma requires water to maintain its viscosity and helping to maintain core body temperature. Our hydration status also plays a role in reducing fatigue and increasing concentration.
Our urine is a good indicator of our hydration status, it should be straw-coloured. Too dark is indicating that we are dehydrated and need to increase our water intake. If it is completely clear, we might well be over hydrated and may be loosing electrolytes if we are urinating excessively.
The recommended daily intakes of water are approx. 2.5 litres for males, and 2 litres for females.
Water is essential for life, and we must replace what is lost in exercise on top of this recommended amount.
For women, it is important to note that our hydration requirements change at different life stages. In pregnancy a woman's intake should increase by 300ml per day to 2.3 litres per day, and while breastfeeding should be 2.7 litres of water per day (as water is required to ensure adequate milk production).
Hydration for Sport
Requirements will vary from person to person, as sweat losses are uniquely individual. Hydration plays a role in strength and endurance, and so is an important consideration for recreational exercises and athletes alike.
A decline of 2% of body weight through sweat loss results in a reduction in performance for athletes. During challenging sporting events an athlete may lose up to 10% of their body weight and so hydration status is a significant concern in athletic performance and the sporting world.
Sports drinks are a convenient way for athletes and recreational exercisers alike to restore their energy, electrolyte and water balance before, during and following exercise.
When reaching for the sports drinks, it is important to understand what each type is and what it’s intended use is, as sports drinks are readily available and are recognized as a major advance in sports nutrition by supporting performance through the provision of carbohydrates and hydration.
Isotonic drinks
These sports drinks have a similar water, salt and carbohydrate composition to our blood composition. They are designed to be used during exercise, as the components take longer to reach the bloodstream than those contained in hypertonic solutions. They provide a great source of carbohydrate and are suitable for shorter, high intensity workouts. These drinks can contain a high amount of sugar and may cause gastrointestinal cramps and discomfort.
Hypertonic drinks
These drinks contain a high concentration of carbohydrates. They are designed to replenish carbohydrates after a sustained energy output (for recovery) or to stock up on carbohydrates before exercise to top up glycogen stores. Due to the hypertonic solution, they may lead to dehydration, as water is required to dilute the solution for absorption. So when using these drinks, it is essential to dilute with water or consume water alongside hypertonic solutions.
Hypotonic Drinks
These are the most readily absorbed of the sports drinks formulas. Hypotonic drinks are absorbed in the gut by osmosis, as they contain a lesser amount of carbohydrate and electrolyte than blood. These drinks focus on hydration, and so they offer fewer carbohydrates to the athlete. These drinks are ideal for hydrating on the move, as they cause less gastrointestinal discomfort. Hypotonic solutions are ideal for endurance events and training and can be taken in combination with nutrition supports to maintain adequate hydration and prevent muscle cramps and fatigue.
For athletes who wish to adequately replenish their hydration status, a simple rule of thumb can be applied: for each 1 kg of weight lost, aim to replace 1.5 litre of water, minus the amount of water consumed during the exercise period. So for example, if I've lost 500g, having consumed 250ml during exercise, then I should aim to consume 500ml of water.
This measurement should be repeated a few times and the athlete will begin to learn how their training regime affects them and in time will come to know what their body requires following exercises they perform regularly. Ideally the weight lost should reduce over time when applying this method, weight loss represents dehydration whereas, in the event of weight gain during exercise the athlete has over hydrated.
The athlete should also consider salt and carbohydrate replacement by eating shortly after exercise, ideally within 30 minutes, to support efficient recovery.
Bibliography:
Kenefick R and Cheuvront S (2012) Hydration for recreational sport and physical activity. Nutrition Reviews. (supplement 2).
Popkin B et al. (2010) Water, Hydration and Health. Nutrition Reviews 68(8).
Rowlands D et al. (2022) The Hydrating Effect of Hypertonic, Isotonic and Hypotonic Sports Drinks and Waters on Central Hydration During Continuous Exercise: A Systematic Meta-Analysis and Perspective Sports Medicine 52.
Shaun S et al. (2018) Sports Drinks on the Edge of a new Era. Current Sports Medicines Reports 17(4).
Shireffs S (2009) Hydration in sport and exercise. Nutrition Bulletin 34(4).
