2.0 Fluid requirements in Training and Competition
2.1 The four stages of rehydration
2.2 Fluids available for rehydration
2.3 Choosing and preparing a sports drink
Section 2.0: Fluid Requirements in Badminton
Fluid is very important for optimal performance. Sweat and respiratory fluid losses are high in badminton as courts are often very hot and crowded. Air-conditioning may not be in use.
The Importance of Fluid in Sport
- Thermoregulation, cooling the body
- Transport of oxygen and nutrients to muscle and brain
- Removal of metabolic waste products (lactic acid, CO2)
- Maintenance of blood pressure
- Digestion and absorption of nutrients
- Cushion the brain
- Cellular hydration and function
- Joint lubrication
After considering the many essential roles of fluid within the body it is easy to appreciate that dehydration is associated with a rapid and significant decline in performance. Fluid loss that equates to just 1% of body weight (700g in a 70Kg athlete) is associated with a decline in performance, while a 2% fall in body weight is accompanied by a 10% loss of VO2 max, impaired cognitive function, poor concentration, increased risk of injury, reduced oxygen/nutrient delivery to muscle, reduced clearance of metabolic end-products (lactic acid, CO2) and increased fatigue.
2.1 The 4 Stages of Rehydration
Fluid Intake – Aim to replace fluid losses and maintain fluid balance by staying within 1% of pre-exercise body weight
Gatrointestinal Absorption – Maximise absorption of fluids through the gut wall to prevent gastic problems; bloating, nausea, fullness. Carbohydrates (usually as glucose) and sodium both promote rapid absorption, enabling large volume to be drunk without gastric upset.
Retention in Plasma – Retention of fluid in the plasma is achieved by preventing dilution of plasma electrolytes, to ensure that urinary output is limited, by replacing electrolytes (especially sodium) that have been lost in sweat.
Cellular Rehydration – Redistribution/replenishment of potassium into cells to ensure cellular rehydration. Usually accomplished in recovery by eating potassium rich foods.
Stage 1: Fluid Intake
How much fluid?
* A sedentary person needs 2-3 litres of fluid each day to replace losses, approximately half of which will come from drinks, the remainder from food.
* An athlete can lose 1-11/2 litres of fluid in an hour
* Realistically fluid replacement may not keep pace with losses, however an athlete should be well practiced in replacing a litre of fluid an hour, which is the amount that can usually be drunk without gastric upset.
* Athletes with high fluid requirements should drink a 300-500ml fluid bolus 30 minutes before exercise to boost pre-training fluid status.
* Many factors influence fluid requirements, all should be taken into account before training/ competition.
- Ambient temperature/ humidity: losses increase as temperature and humidity increase
- Exercise intensity: Fluid losses increase with intensity
- Acclimatisation: physical adaptation to local conditions may reduce losses
- Clothing: layers trap heat and increase sweating, synthetic fibers may cause excessive sweating
- Pre-training hydration: early dehydration is usually due to poor pre-exercise fluid status
- Training status: endurance training increases body cooling responses, hence sweating increases
¨ Fluid requirements are ‘dynamic’ and can change daily
¨ Thirst is a very poor indicator of fluid status
Monitoring Hydration Status
* Calculating individual fluid requirements for a variety conditions is a process of trial and error
* Training, not competition, is the time to assess fluid requirements
* There are several methods available for assessing hydration status, the most practical are a) Urine colour; should be pale lemon (apart from first wee of the day) b) Pre-exercise vs. post-exercise body weight: weigh with as few clothes on as possible, aim to remain within 1% of pre-exercise weight. Each kilogram weight reduction is equivalent to a fluid deficit of 1 litre.
Stage 2: Absorption of Fluid
Oral rehydration fluids, such as Dioralyte, contain low amounts of carbohydrate, and high sodium (Na+) and potassium (K+) concentrations compared to sports drinks (table 7). This is because sports drinks are designed not only to rehydrate, but must also be palatable (so that large quantities can be drunk) and provide energy to delay fatigue by maintaining blood glucose levels. Sports drinks are therefore a compromise between optimum hydration and energy provision.
Preparations such as Dioralyte contain are optimum for rehydration, as we move away from their composition rehydration is not as rapid, but energy levels are also maintained.
When deciding on the composition of a sports drink it is necessary to decide how important fluid, energy and a combination of the two is to performance. However, in extreme heat, rehydration always takes priority. In Figure 4 shows that hypotonic fluids are absorbed most rapidly through the gut, meaning that large volume can be drunk with minimal gastric distress and maximum rehydration potential.
Badminton players have moderate energy requirements, but generally high fluid requirements. Therefore, hypotonic fluids should be the fluid composition of choice for most players.
The absorption of water is slow as it is not actively absorbed through the gut, but dragged through with glucose and sodium. Thus water is not a good choice for rehydration during exercise. Hypotonic fluids are absorbed rapidly because they contain both carbohydrate (usually as glucose) and sodium in the optimum concentrations for absorption and hence rehydration.
Stage 3: Retention
Sodium has a dual role in rehydration, firstly it aids absorption through the gut and secondly it replaces sodium in plasma that has been lost in sweat. If sweat losses are high, plasma sodium concentrations fall and if fluids are drunk that contain little or no sodium the concentration of plasma sodium will be further diluted. Low sodium concentrations are the trigger for the kidneys to increase urine output, resulting in high fluid losses in spite of dehydration.
Although sports drinks contain low concentrations of sodium, when combined with the salt eaten in many foods during recovery, retention of fluid should be adequate. However, if where fluid losses are high, drinks are homemade, or when isotonic sports drinks are diluted down to hypotonic drinks (see ‘Preparing a sports drink’) more salt should be added to reduce urinary losses.
The final stage of rehydration involves moving fluid from plasma into cells. Potassium is largely responsible for this process. Although sports drinks do contain some potassium, its value during exercise is uncertain. ‘Recovery’ appears to be the most important time for replacing potassium (refer to section 3.0)
2.2 Fluids Available for Rehydration
Water: not suitable for replacing fluids when losses are high as absorption is very slow, also the benefits of energy and sodium are absent.
Hypotonic Fluids: contain 2-4% carbohydrate, rehydrate rapidly, and enabling large quantities to be drunk. Useful in sports where fluid requirements are high, but duration and energy requirements are moderate, such as badminton.
Isotonic Fluids: contain 6-8% carbohydrate, as glucose and glucose polymers. Useful in endurance sports to preserve glycogen and delay fatigue, such as a marathon. These fluids can cause discomfort when drunk in large quantities, but are useful in ‘recovery’ (section 3.0)
Hypertonic Fluids: contain over 10% carbohydrate and are not usually used in sport for rehydration
2.3 Choosing and Preparing a Sports Drink
Hypotonic Drinks ( 2-4% carbohydrate)
a) Commercial Brands: few hypotonic brands exist, Lucozade low-calorie is still available. The simplest method for making a hypotonic fluid is to dilute an isotonic preparation with twice the water advised and add a pinch of salt to restore sodium content.
b) Fruit juice: water: Fruit juices usually contain 26g of carbohydrate per 250ml. Make a litre of hypotonic fluid with 250-300ml of fruit juice to 750-700ml of water. Add a pinch of salt
c) Regular Squash: water (do not use the ‘No added sugar’ varieties). Ribena ‘lite’ falls into this category, but not regular Ribena which has a much higher sugar content. 100ml of regular squash to 900ml of water will make a hypotonic solution. Add a pinch of salt.
Isotonic Drinks (6-8% carbohydrate)
d) Commercial Brands: Many brands exist as powders, ready mixed, gels etc. Lucozade Sport, Gatorade, Isostar (contains caffeine) and SIS Go are examples. Commercial brands can be more convenient than homemade varieties, but are more costly.
e) Fruit juice: water- Add fruit juice to water 50:50, i.e. 500ml juice to 500ml water Add a pinch of salt.
f) Regular Squash: water- Dilute 200ml of squash to 800ml of water. Add a pinch of salt.
Hypertonic Drinks (>10% carbohydrate)
Not recommended for fluid replacement, but may be used where rapid energy replacement is necessary and fluid requirements are secondary, although this situation is unlikely in badminton. Examples include Carbo Force, Maxim, Ultra Fuel, Coca Cola, Red Bull. Many also contain caffeine that may exacerbate dehydration.
2.4 A Summary of Fluid Requirements in Badminton
- Fluid requirements are usually high in badminton
- Fluids should be drunk before, during and after play
- Players should learn to comfortably drink a litre of fluid an hour
- Hydration status is directly linked to performance
- A small change in hydration can have a large effect on performance
- A player’s fluid requirement is individual and dynamic. Urine colour and weight changes are practical methods to assess fluid intake adequacy.
- Sports drinks must contain both carbohydrate and sodium to promote both absorption and retention of the fluid.
- A hypotonic fluid will meet the energy and fluid need of most players.
- Homemade sports drinks are as effective as commercial brands
- Caffeine and alcohol should be avoided
- Non-training day provide an opportunity to fully rehydrate
- Competitions are not the time to practice fluid requirements and appropriate composition