Nutrition Strategies for the Marathon and Half Marathon

1. Nutrition Strategies for the Marathon and Half Marathon Adrian Holliday School of Sport & Exercise Sciences University of Birmingham axh547@bham.ac.uk

2. Workshop Outline • Importance of good hydration • Physiological effects of dehydration and effects on endurance performance • How do we know when we are dehydrated? • Guidelines for fluid intake during endurance running • Challenges to these guidelines – can we drink too much? • Fluid intake strategies and recommendations

3. Workshop Outline • Fuel used during endurance running • Importance of carbohydrates • Carbohydrate intake during endurance events – when, how much, what form? • Carbohydrate during shorter endurance events – can we trick the brain? • Feeding strategies and recommendations

4. Workshop Outline QUESTIONS AND DISCUSSION!!

5. Hydration and Fluid Replacement during the Marathon

6. Importance of good hydration Heat Gain Solar radiation Reflected radiation EXERCISE WORK Heat Loss Respiration Radiation Convection Evaporation - SWEATING For every L of oxygen consumed 16 kJ of heat is produced and only about 4kJ of mechanical work

7. Sweating for Regulating Body Temperature Most effect mechanism for heat loss and thermoregulation in humans. Evaporation of 1L sweat releases ~600kcal or 2.4MJ of heat energy from the body. http://www.youtube.com/watch?v=826HMLoiE_o

8. Estimates of common sweat rates. Our lab record for sweat rate = 3.16L/h

9. Effects of dehydration -2% BW Reduced sweat rate Poor heat dissipation Decreased plasma volume Decreased blood flow to the skin Impaired thermoregul-ation -3-5% BW Premature fatigue Performance Dehydration Decreased cardiac output Decreased flow to the exercising muscles Increased use of muscle glycogen Impaired cognitive function Core temp Heat exhaustion Heat stroke -6% BW

10. Guidelines for fluid replacement during the marathon It is well-documented that a loss of fluids equating to just 2% of your body mass will have a very detrimental effect on performance. “Drink 8-10 fl oz [230-300ml] every 10-15 min during exercise.” Up to 1.8L/hour

11. “Drink to replace 150% of water loss” “Drink every 10-20 minutes.” “The evidence on this is clear. If your event or workout is longer than 30 minutes you should be drinking a sports drink.” “Drink as much as possible” – American College of Sports Medicine, 1987-1996 “Rates of fluid intake of up to 1.6L/hour” – ACSM

13. Sports drinks are preferable to water alone • Addition of sodium and carbohydrate can increase fluid absorption and retention. • However, once carbohydrate exceeds ~ 10%, fluid delivery will decrease to adverse osmolarity of the drink. Sport drink for fluid replacement should: • Be isotonic • Contain sodium ~ 40-80mg/100ml • Contain carbohydrate ~ 4-8g/100ml • Not be too acidic or gassy • Be palatable

14. Start well hydrated. How do I know if I am well hydrated? • Regular monitoring of body weight – morning, pre- and post-training and racing • Urine volume – normal = 1.8-2 litres/day • Urine colour

15. Why these changes in guidelines? What about hyperhydration? Can we over-drink?

16. What about hyperhydration? Can we over-drink? YES!! Over-drinking can occur through: • Water intake > water loss (sweat rate) • Large volume of water are ingested in single episode Can lead to: • GI tract discomfort • Unwanted weight gain • Urinating • Decreased performance • HYPONATREMIA – low blood sodium concentration

17. Hyponatremia – low blood sodium Water and Sodium Out Water In

18. Prevalence of Hyponatremia: • Boston Marathon, 2002 • 488 finishers (63% of field) – weighed pre- and post-race. Blood sodium levels measured. • 63 (13%) clinically hyponatremic (<135mmol L-1) Fatalities: • 1 death in London Marathon, 2007 • 1 death in 2002 Boston Marathon. • 8 reported deaths in USA, inc military. • Tim Noakes, “no known cases of death from dehydration during the marathon”

19. Symptoms: • Dizziness • Confusion • Headaches • Exhaustion • Cerebral edema • Respiratory distress • Seizure, coma. Risk Factors: • Weight gain during the race. • Finishing time for the marathon >4 hours. • Extremes in BMI – particularly small or large body size.

20. Constructing your individualised drinking strategy • Discover your specific sweat rate • Weigh yourself before and after a training run at race pace, under similar environmental conditions to those expected on race day and lasting ~ 1hour. • Wear minimal clothing for weighing and dry yourself after run. • Sweat rate ml/hour = pre-run weight (kg) – post-run weight (kg) + fluid intake (L) – water loss through urine (L). Example: Pre-run weight = 65.4kg, post-run weight = 64.6kg, fluid intake, 0.2L, 0L urine. 65.4kg – 64.6kg = 0.8kg = 0.8 L water 0.8 L + 0.2 L = 1L/hour

21. So… 65.4 kg body weight Max acceptable weight-loss = 2% = 1.3kg Maximum water loss = 1.3L Sweat rate = 1L/h 3 hour marathon = -3L So we should consume at least 1.7L If this is spread evenly over the 3 hour period… 1.7 / 3 = 0.6L/hour = 200ml every 20 minutes minimum intake! NOW, TRY THIS IN TRAINING!!

22. Summary and Recommendations • Small amount of dehydration (~2% loss BW) impairs thermoregulation mechanism which may effect endurance performance. • Greater dehydration (~3-5%) impairs muscle metabolism and endurance performance. • Severe dehydration (≥6% loss BW) = heat exhaustion, heat stroke, coma, death. • Over-drinking can lead to hyponatremia, which will impact upon endurance performance and can be fatal! • Hyponatremia is a more serious, common health concern than dehydration during marathon running!

23. Summary and Recommendations In warm weather: • Fluid balance is very important for thermoregulation • Avoid any dehydration • Match fluid loss with fluid intake In temperate weather: • Avoid dehydration leading to weight loss >2% body weight. • A little dehydration is not a bad thing in this case. • Avoid weight gain. In all conditions: • Avoid over-drinking! • Fluid intake should not exceed fluid loss.

24. Summary and Recommendations Fluid intake: • Measure individual sweat rate during training at race pace by weighing before and after run. • Sports drinks are preferable to water alone. • Try drinking to thirst in temperate weather. Thirst may be an inadequate mechanism during warm/hot weather. • Practice your drinking strategy in training (type of drink, amount, frequency, method). Do not try anything new on race day. • Ensure that you start the race in a good hydration state. • When you have an established drinking strategy, check it with pre- and post-race weighing.

25. Carbohydrate feeding during the marathon

26. Fuel utilisation during endurance exercise Marathon pace Carbohydrates are important!

27. 7kg fat ~63000 kcal Run @ 80% VO2max for... ~54 hours!! 70kg Male 10% Body Fat VO2max = 75 ml kg-1 min-1 ~ 400g CHO ~1600 kcal Run @ 80% VO2max for... ~ 80 minutes!! Glycogen Depletion – Hitting the Wall!

28. Maintaining carbohydrate availability is very important! Ensures high rates of energy production to maintain high rates of work output – fat alone can rarely achieve this! Drop in carbohydrate availability will result in reduced endurance performance. Our stores of carbohydrate will become depleted rapidly when exercising at high intensities Blood glucose becomes very important. HOW CAN WE MAINTAIN BLOOD GLUCOSE LEVELS?

29. Carbohydrate feeding during exercise DOES increase endurance capacity and endurance performance in events lasting >2hours!

30. Cycling 70% VO2max 4 hours Little evidence of glycogen sparing Maintenance of blood glucose

31. Carbohydrate feeding strategy • How much carbohydrate? • When should I take it? • How should I take it – in what form? • What type of carbohydrates should I be consuming?

32. How much carbohydrate should I ingest? • Ideally, rate of 1.4g/min or ~80-85g/hour for optimal rates of exogenous carbohydrate oxidation. • However, this can lead to GI tract distress for many individuals. • GI tolerance is highly individualised, but also very trainable! How often should I be feeding during a race? • GI tolerance is increased with smaller, more frequent intakes. • But, does this take too much time?

33. Type of Carbohydrate • Using a mix of sugars has been shown to result in greater carbohydrate delivery and oxidation rates • 2:1 glucose : fructose mix provide optimal exogenous carbohydrate oxidation • http://www.youtube.com/watch?v=EzMBltt31uc

34. Form of Carbohydrate • No preferential form (solid vs. liquid vs. gel) with regard to absorption. • But, can’t chew when running! • High intakes are difficult from carb. Drinks. Gels provide the most concentrated dose. • Personal preference and GI tolerance

35. To formulate your individual strategy…. Practise in training! • Amount • Form • Brand • Dosing & frequency • Water intake (gels are very difficult to take without water)

36. What about events lasting <2 hours? Initial considered of no benefit to feed during shorted endurance events • Glycogen depletion not an issue. • Blood glucose remained sufficiently high • Sufficient carbohydrate availability. But, recent evidence of effect of carbohydrate on the brain…. WITHOUT EVEN CONSUMING THE CARBOHYDRATE!

37. Carb. mouthwash has been shown to improve endurance performance during lasting ~ 1 hour. Increased brain activity Decreased perception of effort Decreased fatigue Improved performance

38. Mechanism is unknown But, could we be “tricking” the brain into thinking we are getting a fuel boost? The brain thinks that it has a greater potential for endurance capacity. Fits with Tim Noakes’s Central Governor Theory of fatigue. http://opencontent.uct.ac.za/Humanities/Tim-Noakes-The-body-is-willing-but-the-mind-is-weak-Or-is-it-the-other-way-around

39. For any endurance event…. Start with full glycogen stores! Muscle glycogen • Muscle glycogen can become completed over time repeated bouts of high intensity/prolonged exercise (your training). Ensure stores are fully stocked on race by: • Consuming a high carbohydrate diet in the days leading up to the race. • Tapering your training. Training bouts

40. Summary and Recommendations • Carbohydrate is a vital fuel for the marathon and half marathon. • The body has only a small store of carbohydrates. • For prolonged, intense exercise lasting >2 hours, blood glucose must be maintained to sustain work output. • Carbohydrate feeding will maintain blood glucose levels, maintain carbohydrate availability for working muscles. • Carbohydrate feeding during the marathon will improve performance!

41. Summary and Recommendations • Rates of intake of a carbohydrate mix (glucose and fructose) in the region of 1.4g/min or 85g/hour will produce the highest rates of carbohydrate oxidation. • Experiment with your own carbohydrate feeding strategy in training. • Persist with your feeding strategy as the GI tract is trainable with regard to tolerance of intake. • Do not try anything new on race day. • Carbohydrate mouthwash may help improve performance in events lasting < 2hours. • Evidence is far from conclusive, so again try it in training and assess benefits for yourself. (cost/benefit analysis).

42. Useful Resources ACSM Position statement for fluid replacement -http://journals.lww.com/acsm-msse/pages/default.aspx?sessionEnd=true Book: Sport Nutrition. Jeukendrup & Gleeson Tim Noakes and the Central Governor Thoery podcast - http://opencontent.uct.ac.za/Humanities/Tim-Noakes-The-body-is-willing-but-the-mind-is-weak-Or-is-it-the-other-way-around