LGB 509 Sports Nutrition Fluid balance Aims 1

LGB 509 Sports Nutrition – Fluid balance

Aims 1. Describe the need for fluid during exercise. 2. Explain the factors affecting heat and sweat loss. 3. Describe the effect of dehydration on the cardiovascular system. 4. Provide recommendations for fluid intake before during and post exercise.

Introduction to body water Body water About 50 -60% of our body mass is water. Lean tissue mass = body water content. Lean tissue e. g. muscle, liver, heart etc…contains about 75% whereas nonlean tissue or fat mass only contains 5% water. Females will tend to have a lower body water content, due to higher proportions of fat mass. Any water loss needs to be replaced, along with any electrolytes.

Heat production during exercise For every 1 L of oxygen consumed approximately 4 kcal of heat is produced. Only 1 kcal is used for mechanical work, making the process inefficient. Large muscle groups such as the quadriceps can have temperature increases of 1°C/min. Thus the heat is transferred to the core to be sensed by the brain, more specifically thermoreceptors located in the hypothalamus. • ability to 'read the play/situation' • acquired knowledge • decision-making skills

Heat storage and loss Heat storage • It can be dangerous if the body temperature gets too high. • Above 39. 5°C central fatigue kicks in, so this needs to be avoided where possible. A higher starting body temperature will result in a higher final body temperature. So if reaching high body temperatures is a concern strategies should be put into place. • Heat exhaustion will occur when heat production occurs at a faster rate than dissipation. Heat loss • To understand heat loss we need to understand about the transfer of water particles and how this can occur. • If the environment is cooler than the skin then heat can be lost, if the environment is warmer then heat gain will occur. If the air is saturated with water vapour (100% humidity), evaporation will not occur.

Ways heat is lost Radiation: The transfer of energy from one object to another e. g. a person to the pavement. Convection: The exchange of heat between a solid (e. g. human) to a medium that moves (e. g. the air), e. g. from muscle mass to blood flow to the CNS. Conduction: The transfer of heat from adjoining particles, from areas of high heat to low heat, e. g. within the muscles. Evaporation: A combination of convection and conduction. 1 L of sweat evaporated from the skin = 593 kcal of heat.

Factors affecting heat loss Volume and speed of sweat loss Clothing Factors affecting heat loss Humidity of the local environment Dehydration

Daily fluid balance Fluid gain • Fluid loss 1700 ml • • Drinking Eating 200 ml • Metabolic 300 ml Total = 2200 ml • Respiration Skin • Faeces 100 ml • Urine 1300 ml Total = 2200 ml Exercise can cause an additional loss of 500 – 3000 ml per hour 600 ml

Fluid balance Dehydration : to lose or remove water Rehydration : to gain water Euhydration : normal state of body water content Hyperhydration: overhydrated Hypohydrated: underhydrated

Sweat loss How much sweat do we lose? Sweat loss is very individualised and many factors can affect it such as: Temperature Humidity Intensity of the exercise etc… When does it become a problem? 2% body mass loss = detrimental to performance. What is 2% of your body mass? Research ACSM (2009) states 2 -3% water deficit. Goal of drinking is to avoid dehydration, not to drink beyond sweat rates.

Ways of assessing hydration – practical example Sweat loss: Why? 2%, recovery strategy. Weigh yourself before exercise. Commence exercise: take note of what you drink and if you urinate. Weigh yourself after exercise.

Example Body Mass: 60 kg 1 Litre of fluid consumed How much fluid did they lose in the exercise session? Body Mass: 59 kg 2 L

Example Lets complicate it a little further… Body Mass: 60 kg 2 Litre of fluid consumed Body Mass: 59 kg 450 ml of urine loss half way through the session How much sweat did they lose in the exercise session? 2 L 550 ml

Ways of assessing hydration status Urine colour chart Urine OSMOLALITY <300 Well hydrated 300 – 600 Adequately hydrated 600 – 900 Dehydrated 900 – 1400 Severely dehydrated Armstrong (1994)

Ways of assessing hydration status 2 Thirst mechanism – encourages fluid consumption. However this is a poor indicator. If you feel thirsty it is likely you are already dehydrated.

Fluid loss through sweating – 1 kg = 1 litre!! 1 g = 1 ml

Effects of dehydration – why are these a bad thing? Dehydration negatively affects performance Reduced maximal capacity of the heart Reduced VO 2 max Reduced blood volume Decreased skin blood flow Decreased sweat rate Decreased heat loss Increased core temperature Increased rate of muscle glycogen use Organ failure = Death

Effects of dehydration Heart Rate (bpm) The effect of dehydration on heart rate during 2 hrs of cycling 160 Dehydrated 140 Hydrated 120 0 0 Exercise Time (min) 120 Figure 1 Amended from Jeukendrup and Gleeson (2010, p. 199)

Hydration strategies – volumes and timings Type • Isotonic • Palatable • Chilled • Flavoured/Sweetened • Non-acidic/gassy Pre exercise • 2 hr before = 500 ml. • An additional 500 ml 15 minutes before for prolonged exercise. Post exercise • 150% of body mass losses in fluid. • 1. 5 L for every 1 kg in body mass lost. During exercise • 120 -180 ml every 15 -20 minutes. • Essentially enough to match losses but Recommendations based on ACSM (2007) to NOT put on body mass.

Hydration strategies – type of drink Type of drink Description Provide fluid but only very low levels of CHO and are Hypotonic – ideal for those who need fluid without extra calories – lower jockeys, dancers, gymnasts. osmolality than body fluids. Isotonic – same osmolality as body fluids Contains same number of particles of dissolved substances as plasma. Replace fluid quickly with a useful boost of CHO. Not suitable for most athletes as the fluid takes a long Hypertonic – time to empty from stomach and can cause cramps. The higher exception being ultra endurance events (Td. F). osmolality than body fluids

Summary • A persons body water percentage is dependant on their body composition. • Producing energy is fairly inefficient with regards to heat production therefore we need to regulate our core temperature. • You do NOT want to be more than 2% dehydrated. • Being hydrated is important to maintain high levels of performance. • Nutritional strategies and fluid choices vary from performer to performer.

References ACSM (2007) ‘Exercise and fluid replacement’. Medicine and Science in Sport and Exercise, 39 (2), pp. 377 -390 ACSM (2009) ‘Nutrition and athletic performance’. Medicine and Science in Sport and Exercise, 41 (3), pp. 709 -731. Armstrong, L. E. , Maresh, C. M. , Castellani, J. W. , Bereron, M. F. , Kenefick, R. W. , La. Gassee, K. E. and Riebe, D. (1994). ‘Urinary Indices of Hydration Status’, International Journal Of Sports Nutrition, 4, pp. 265 -279. Jeukendrup, A. E. and Gleeson, M. (2010) Sports Nutrition: An introduction to energy production and performance. 2 nd edn. Leeds: Human Kinetics Maughan, R. J. (1991) ‘Fluid and electrolyte loss and replacement in exercise’. Journal of Sports Science, 9, pp. 117 -142.