Title: Preparing for the Olympic marathon in Athens 2004

 

Key words: marathon, runner, running, Olympic, Olympics, humidity, heat, respiratory problems, heat exhaustion, heat stress, sports physiology, sweat, sweating, fluid intake, dehydration, cardiovascular fitness, plasma volume, VO2, core temperatures, blood osmolality, viscosity, heat stroke, performance, exercise, splanchnic, blood flow, hyperthermia, ischaemia, gastric emptying, acclimatisation, rehydrate, sports drinks, training, electrolyte losses, glycogen, stores, hypoglycaemia, sport beverage, glucose, glucose polymers, sodium, sodium loss, hydration, coffee, alcohol, consumption, diet,

 

Date: Oct 2006

 

Category:

 

Nutrimed Module:

 

Type: Article

 

Author: Morgan, G

 

Preparing for the Olympic marathon in Athens 2004

To the elite marathon runner, the Olympic marathon poses the ultimate sporting challenge, not only from the competitive but also from the physiological point of view. No more is this true than for the Athens marathon in 2004 which will be run in hot and humid conditions during the summer. Even during the cooler part of the race day, this will present a severe challenge to the runners. The physiological problems posed by these conditions will be considered in this paper.

 

Athens, topography and environment

Athens is situated in the southern European Mediterranean area with daytime summer temperatures rising to 40 C and with moderate levels of humidity. Predictable high temperatures are envisaged for the Olympic Games with a low probability of cloud cover or rain. The flat course between Piraeus and the Olympic Stadium in Athens will run through a heavily industrialised area of Greece. Air quality will be poor, adding to the difficulties posed to athletes with respiratory problems, and there will be minimum shadow cover provided by trees and buildings. Athletes will therefore be exposed to the full heat of the Athenian sun.

 

The physiological problems posed by Athens 2004

The pictures of Jim Peters in a state of heat exhaustion staggering to the finishing line in the 1954 Empire Games in Canada, serves as a reminder of the dangers of hyperthermia and dehydration to even well-conditioned elite marathon runners. Since that time the stress imposed by heat during the course of a marathon event has been more adequately described by sports physiology. Regimes to counter heat stress have also been put on a more scientific footing. Given the conditions and the nature of the event in Athens, the following points relating to heat stress are pertinent.

Heat production by the body rises some ten times with severe exercise, to 75-90 KJ/min. If this heat was not dissipated it would lead to a 1 C rise in body temperature every 5-7 mins. (Brouns 1991).

At maximum rates of sweating, the body is able to dissipate 75 KJ/min in heat (Brouns 1991).

Sweat losses of up to 35mls/hr can occur. During the course of an Olympic marathon this would amount to some 4 litres of sweat (Brouns 1991).

The maximum fluid intake which is practical for an athlete to take during competition is 600 mls/hr (Noakes 1988). With 500 mls taken prior to the event (American College of Sports Medicine recommendation 1984), this amounts to a fluid intake of around 2 litres for a runner completing a marathon in 2 hours. The estimated loss of body weight would be around 3% for a 70 Kg runner.

A 2% loss of body weight due to dehydration has been shown in many surveys to impair performance (Williams 1985). The effect is more marked with increasing levels of dehydration so that with, for example, a 5% loss in body weight a 30% drop in work capacity occurs (Saltin & Costill 1988).

Sweat losses are not related to the final marathon time but simply to the distance covered and the race conditions (Maughan 1985)

 

Training and heat acclimatisation

Training improves cardiovascular fitness. Maximal cardiac output, VO2 max and plasma volume increase enabling the circulation to maintain stable venous and arterial pressures for longer during periods of dehydration (Convertino 1983). Heat acclimatisation leads to a further increase in plasma volume (Mitchell 1976), increasing this effect. Training in hot conditions leads also to a further increase in the sensitivity and volume of sweat production (Brouns 1991). This helps lower core temperatures but at the expense of increased fluid losses.

 

The consequences of dehydration and hyperthermia

Some degree of dehydration and impaired performance are inevitable during the Athens marathon. The major effects on the athlete relate to:

1) The cardiovascular system. Dehydration leads to contraction of plasma volume and increased blood osmolality and viscosity. Hyperthermia is a direct result of increased osmolality (Greenleaf 1974, Harrison 1978) and may lead to heat-stroke. Impaired oxygen tranport resulting from compromised muscular perfusion will effect performance.

2) The skin. In an effort to maintain plasma volume and the flow of blood to the exercising muscles, blood is shunted away from the skin leading to impaired skin perfusion, a compromised sweat response and hyperthermia (Brouns 1991). 3)

 

The gastrointestinal tract.

Gastrointestinal problems have been reported in up to 83% of marathon runners (Halvorsen 1992). Heartburn, diarrhoea and flatulence are the major complaints. The normal reduction in splanchnic blood flow that occurs during exercise is exaggerated during dehydration and may lead to total vascular shutdown with ischaemia of the bowel. Gastrointestinal bleeding has been reported in 20% of runners and fatalities have occurred as a result (Thompson 1982,Halvorsen 1986). Delayed gastric emptying further compromises the ability of the body to rehydrate (Rehrer 1990).

 

Strategies to optimise performance in Athens

Minimising the dangers of dehydration and hyperthermia will be the focus of efforts to maximise marathon performance in Athens. Training and acclimatisation are critically important but other measures such as the wearing of suitable clothing to optimise heat loss, appropriate rehydration measures and structured rest periods are areas of concern that need to be addressed. Issues such as electrolyte losses in the heat and the maintenance of glycogen stores are also important. Hypoglycaemia associated with exhausted glycogen stores can often mimic or be associated with heat exhaustion and requires the same preventative regime as in more clement conditions.

 

The ideal sport beverage

Many studies have now been carried out looking at the effect of sports beverages on prolonging athletic performance in endurance events. Because of the trial designs, which usually involve overnight fasting, results have been variable and difficult to transpose to a race setting. The general consensus is that beverages both prevent dehydration and by supporting glycogen stores prolong the time to exhaustion (see Maughan 1991 for review). With respect to marathon running, Coombes (2000) reported on 8 studies carried out on athletes running for 1 to 2 hours. 6 out of 8 of these studies showed a significant improvement in performance with the beverage, including one (Millard-Stafford 1992) which was conducted in hot conditions with a final 5 Km time trial, conditions which could be said to mimic those in Athens. In the light of these studies, the present recommendation is to take the maximal absorbable intake of these beverages before, during and after the event as already mentioned. Present recommendations are to take a beverage containing less than 10% glucose or a combination of glucose and glucose polymers, as higher concentrations have been found to delay gastric emptying (Schedl 1994). Glucose and electrolytes help to improve palatability, delay glycogen exhaustion and improve hydration (Maughan 1991). Although sodium losses in sweat in the trained individual are not thought to be significant (Costill 1975), there is evidence that in the immediate post-race period giving a higher concentration of sodium in the beverage (up to 77 mmol/litre) could help to restore hydration much more quickly (Nose 1988).

 

Conclusions

The above recommendations can serve only as guidelines to the individual athlete. Individual marathoners have been found to suffer losses of 1-5% of body weight during the course of a marathon with the same fluid intake (Maughan 1985). Individual monitoring during the buildup to the race is therefore of prime importance so that fluid status both before and during the event can be optimised. Complicated biochemical blood analyses are both intrusive to the athlete during the pre-competition phase as well as being unnecessary. Simple charts indicating the degree of urinary concentration are available and this, in combination with body weight measurements during training, will provide adequate data for the individual athlete competing in such conditions as Athens.

 

As far as possible the athlete should keep to his prearranged pre-race programme in terms of carbohydrate loading and avoid any experimentation with the local diet, in particular being careful to avoid excessive coffee and alcohol consumption which could exacerbate the danger of dehydration. By following these protocols the marathoner would stand the greatest chance of optimising his performance.

 

References

1. Brouns F. (1991) Heat sweat dehydration rehydration: a praxis oriented approach. J Sports Sci 9: 143-152

2. Noakes TD, et al. (1988) The danger of an inadequate water intake during prolonged exercise. A novel concept revisited. Eur J Appl Physiol 57: 210-19

3. American College of Sports Medicine. (1984) Position stand on prevention of thermal injuries during distance running. Med Sci Sports Exercise 16: ix-xiv

4. Williams MH. (1985) Nutritional aspects of human physical and athletic performance. 2nd ed., Charles C. Thomas, Springfield

5. Saltin B & Costill DL (1988) Fluid and electrolyte balance during prolonged exercise. In: Exercise, Nutrition and Metabolism (eds. Horton ES and Tenjung RL), pp 150-158. MacMillan, New York

6. Maughan RJ (1985) Thermoregulation and fluid balance in marathon competition at low ambient temperature. Int J Sports Med 6: 15-19

7. Convertino VA, Keil LC, Greenleaf JE. (1983) Plasma volume, renin and vasopressin responses to graded exercise after training. J Appl Physiol 54: 508-14

8. Mitchell D, et al. (1976) Acclimatisation in a hot, humid environment: energy exchange, body temperature, and sweating. J Appl Physiol 40: 768-78

9. Greenleaf JE, Castle BL, Card DH. (1974) Blood electrolytes and temperature regulation during exercise in man. Acta Physiol Polonica 25: 397-410

10. Harrison MH, Edwards RJ, Fennessy PA. (1978) Intravascular volume and tonicity as factors in the regulation of body temperature. J Appl Physiol 44: 69-75

11. Halvorsen FA & Ritland S. (1992) Gastrointestinal problems related to endurance event training. Sports Med 14: 157-163

12. Thompson PD, Funk EJ, Carleton RA, Sturner WQ. (1982) Incidence of death during jogging in Rhode Island from 1975 through 1980. JAMA 247: 2535-2538

13. Halvorsen FA, Lyng J, Ritland S. (1986) Gastrointestinal bleeding in marathon runners. Scandinavian J Gastroenterol 21: 493-497

14. Rehrer NJ. (1990) Limits to fluid availability during exercise. Vrieseborsch, Haarlem

15. Maughan RJ. (1991) Fluid and electrolyte loss and replacement in exercise. In: Perspectives in Exercise Science and Sports Medicine, Vol 4: Ergogenics: The Enhancement of Sport Performance, ed. Lamb DR & Williams MH. Benchmark Press: Carmel, pp 35-85

16 . Coombes JS & Hamilton KL. (2000) The effectiveness of commercially available sports drinks. Sports Med 29: 131-209

17. Millard-Stafford M, Sparling PB, Rosskopf LB, et al. (1992) Carbohydrate-electrolyte replacement improves distance running Performance in the heat. Med Sci Sports Exerc 24: 930-40

18. Schedl HP, Maughan R, Gisolfi CV. (1994) Intestinal absorption during rest and exercise: implications for formulating an oral rehydration solution (ORS). Med Sci Sports Exerc 26: 267-80

19. Costill DL, Cote R, Miller E, et al. (1975) Water and electrolyte during repeated days of work in the heat. Aviat Space Environ Med 46: 795-800

20. Nose H, Mack GW, Shi X, Nadel ER. (1988) Role of osmolality and plasma volume during rehydration in humans. J Appl Physiol 65: 325-331