Sports Med 2005; 35 (2): 163-181

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 1. Physiological and Nutritional Demands of Triathlon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 2. Nutrition and Triathlon Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 2.1 Pre-Competition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 2.1.1 Carbohydrate (CHO) Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 2.1.2 CHO Ingestion 3–4 Hours Before Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 2.1.3 CHO Ingestion <60 Minutes Before Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 2.1.4 Fluid Ingestion Before Exercise: Euhydration or Hyperhydration . . . . . . . . . . . . . . . . . . . . . . 167 2.2 During Competition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 2.2.1 Maintaining CHO Supply During Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 2.2.2 Maintaining Fluid Balance During Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 2.3 Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 2.3.1 CHO Intake After Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 2.3.2 The Early Hours Post-Exercise (<8 Hours) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 2.3.3 Protein and Amino Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 2.3.4 Restoration of Fluid Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 2.4 Preventing Nutrition-Related Medical Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 2.4.1 Gastrointestinal Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 2.4.2 Endotoxaemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 2.4.3 Hyponatraemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 3. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 Triathlon combines three disciplines (swimming, cycling and running) and Abstract competitions last between 1 hour 50 minutes (Olympic distance) and 14 hours (Ironman distance). Independent of the distance, dehydration and carbohydrate (CHO) depletion are the most likely causes of fatigue in triathlon, whereas gastrointestinal (GI) problems, hyperthermia and hyponatraemia are potentially health threatening, especially in longer events. Although glycogen supercompensation may be beneficial for triathlon performance (even Olympic distance), this does not necessarily have to be achieved by the traditional supercompensation protocol. More recently, studies have revealed ways to increase muscle glycogen concentrations to very high levels with minimal modifications in diet and training. During competition, cycling provides the best opportunity to ingest fluids. The optimum CHO concentration seems to be in the range of 5–8% and triathletes should aim to achieve a CHO intake of 60–70 g/hour. Triathletes should attempt to 164 Jeukendrup et al. limit body mass losses to 1% of body mass. In all cases, a drink should contain sodium (30–50 mmol/L) for optimal absorption and prevention of hyponatraemia. Post-exercise rehydration is best achieved by consuming beverages that have a high sodium content (>60 mmol/L) in a volume equivalent to 150% of body mass loss. GI problems occur frequently, especially in long-distance triathlon. Problems seem related to the intake of highly concentrated carbohydrate solutions, or hyperosmotic drinks, and the intake of fibre, fat and protein. Endotoxaemia has been suggested as an explanation for some of the GI problems, but this has not been confirmed by recent research. Although mild endotoxaemia may occur after an Ironman-distance triathlon, this does not seem to be related to the incidence of GI problems. Hyponatraemia has occasionally been reported, especially among slow competitors in triathlons and probably arises due to loss of sodium in sweat coupled with very high intakes (8–10L) of water or other low-sodium drinks. On Wednesday September 25, 1974, the first 1. Physiological and Nutritional ever triathlon was organised with 9.6km (6 miles) of Demands of Triathlon running, 8km (5 miles) of cycling and 457m (500 yards) of swimming at Mission Bay in the US. One Muscle glycogen and blood glucose are the most of the participants of this triathlon would become important substrates for the contracting muscle.[1-4] the founder of the Ironman on Long Island, Hawaii, Fatigue during prolonged exercise is often associatwhich would catch the attention of the media and ed with muscle glycogen depletion[5,6] and reduced would also allow the sport to develop further. The blood glucose concentrations[7] and, therefore, high Ironman consisted of a 3.8km swim, followed by pre-exercise muscle and liver glycogen concentra180km cycling and 42.2km running. More than two tions are believed to be essential for optimal perdecades later, at the Olympic Games in Sydney in formance. However, Noakes[8] recently suggested 2000, triathlon was listed for the first time as an that it is unlikely that muscle glycogen depletion Olympic discipline. In only one-quarter of a century, ‘alone’ limits prolonged exercise performance. Usa new event had developed into a well organised and ing a simulated Ironman triathlon model, Noakes professional sport with Olympic status and worldpredicted that after 4.5 hours of cycling at an estiwide participation. Triathlon is unique in that it mated exercise intensity of 71% maximum oxygen combines three disciplines (swimming, cycling and consumption (V̇O2max), an elite male Ironman running) and competitions last between 50 minutes triathlete would have almost completely depleted (sprint distance: 500m swim, 20km cycle and 5km his or her carbohydrate (CHO) stores. Interestingly, run) up to 14 hours (Ironman distance). after completion of the 180km cycle, elite triathletes Nutritional practices and nutrition knowledge are able to run at a speed of 16 km/h for another 160 have also evolved rapidly and this review focuses on minutes, which represents an exercise intensity of the importance of nutrition in triathlon. Obviously, >66% V̇O2max. At present, it is not known how it is the physiological demands and the nutritional chalpossible that triathletes are able to complete a full lenges of triathlon depend very much on the duramarathon at such high exercise intensities when tion of the event. Therefore, the physiological decalculations suggest that muscle glycogen stores are mands of triathlon at varying distances is discussed likely to be depleted. Although speculative, it could briefly and this is followed by an overview of curbe that other CHO sources (i.e. lactate) in addition to rent knowledge on preventing fatigue and health those in the active muscle and liver contribute to fuel problems through nutritional measures during oxidation during ultra-endurance exercise. It is also triathlon of varying distance. possible that long-distance triathletes have an  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) Nutritional Considerations in Triathlon 165 increased capacity to oxidise fat, especially when caused by diuretics produced a 3–5% reduction in 1500–10 000m running times.[22] Severe hypohydramuscle glycogen stores are depleted. tion may reduce the rate of gastric emptying while In addition to glycogen depletion, dehydration increasing the likelihood of gastrointestinal (GI) can also impair endurance performance.[9,10] Sweat problems,[23] therefore, hypohydration may become losses occur because there is the need to dissipate a self-perpetuating problem. Most importantly, the heat that is generated during exercise. Data from while hypohydration and hyperthermia alone have the Sydney Olympics report an elite triathlete genernegative effects on performance, their combination ating an average of 264W over the 6-lap cycling is particularly serious, both in terms of performance section.[11] However, this is only a small fraction of and health.[24] the total energy generated by the body as gross mechanical efficiency during cycling has been ob2. Nutrition and Triathlon Performance served to be around 20%.[12] Therefore, it can be estimated that the remaining ~80% or ~1100W is Since physiological demands can be extremely heat energy (discounting the proportion of energy high and hyperthermia, dehydration and CHO deused to maintain homeostasis). This is a large pletion can all affect performance, it is important to amount of heat that, if not lost from the body, would combat these dangers with adequate nutritional cause a large and rapid rise in deep-body temperameasures. This section will discuss whether it is ture. One of the body’s responses to this rise in possible to prevent the reductions in performance temperature is the activation of sweat glands to and where possible, guidelines will be formulated. release sweat onto the surface of the skin for evaporative cooling. Sweat rates will increase with in2.1 Pre-Competition creased metabolic rate (i.e. exercise intensity) and impaired dissipation (i.e. hot, humid, lack of wind) 2.1.1 Carbohydrate (CHO) Loading but can also be highly variable between individuals. The effect of high-CHO diets and elevated musThe loss of body water will result in a reduction in cle glycogen levels on exercise performance has plasma volume, stroke volume and skin blood flow, recently been summarised in a review by Hawley et which can lead to an inability to maintain thermal al.[25] It was suggested that supercompensated mushomeostasis and reduced performance.[13] Therecle glycogen levels can improve performance (i.e. fore, the nutritional challenge is to replace body time to complete a predetermined distance) by 2–3% water and prevent fatigue. in events lasting >90 minutes. However, there seems to be little or no performance benefit of supercomThe reduction in performance is thought to be pensated muscle glycogen levels when the exercise due in part to reduced muscle blood flow. In addiduration is <90 minutes. Triathletes preparing for tion, it has been observed that muscle glycogen Olympic-distance triathlons and certainly long-disbreakdown is increased with increasing core body tance triathlons are likely to benefit from CHO temperature,[14-16] although others have shown that loading regimens, although this has never been testfatigue may occur before muscle glycogen is depleted directly. ed.[17] More recently, the effect of hyperthermia on performance has been suggested to be related to The ‘classical’ glycogen supercompensation promore central mechanisms, related to the attainment tocol as was first described by Bergström et al.[5] of a high deep body temperature.[18,19] There is genconsisted of a glycogen-depleting exercise bout foleral agreement that the reductions in body water lowed by a 3-day low-CHO, high-fat/protein diet need only be small for negative performance effects and a 3-day high-CHO diet. This procedure was to occur.[9,20] Walsh et al.[21] reported that reductions found to increase muscle glycogen stores by more in body mass of 1–2% resulted in a 44% reducthan twice the normal glycogen concentration. More tion in performance while a 3% hypohydration importantly, pre-exercise muscle glycogen concen 2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) 166 Jeukendrup et al. tration was directly related to endurance capacity then rest afterwards while consuming a moderateCHO diet. (time to fatigue). Although this ‘classical’ glycogen In summary, well trained triathletes who are aimsupercompensation protocol was successful in eleing for high muscle glycogen concentrations prior to vating muscle glycogen stores, the practical significompetition should make sure that their carbohycance of such a dietary-training regimen is questiondrate intake is high (10g of CHO/kg BW/day) at able as this regimen is very strenuous and may least 1 day before the event and they should make promote both injury and GI distress. sure that 1–4 days before the event, muscle glycogen A study by Sherman et al.[26] demonstrated that concentrations have been reduced significantly. This muscle glycogen stores could be supercompensated can be achieved by a longer training session at with less drastic exercise and dietary manipulations. moderate intensity[26,27] or a short-term high-intensiSherman et al.[26] showed that 3 days of a moderate ty exercise bout.[28,29] CHO intake (50% of energy intake coming from CHO [En% CHO] and ~5g of CHO/kg bodyweight 2.1.2 CHO Ingestion 3–4 Hours Before Exercise (BW)/day) followed by 3 days of a high-CHO intake Pre-exercise CHO ingestion may enhance CHO (70 En% CHO and ~8g of CHO/kg BW/day) in availability during prolonged exercise by increasing combination with a tapered training regimen also muscle and liver glycogen stores prior to exerresulted in supercompensated muscle glycogen concise,[31] or by providing a source of glucose in the centrations. gut for later release into the bloodstream. Ingestion of CHO before exercise may be particularly imporRecently, Coyle et al.[27] demonstrated that contant when exercise is undertaken in the morning sumption of a high-CHO diet (88 En% CHO and after an overnight fast and hence liver glycogen ~12.5g of CHO/kg BW/day) during six consecutive stores are substantially depleted, or when there has days of training can lead to extremely high muscle been inadequate time for complete restoration of glycogen concentrations. The data of Coyle et al.[27] muscle and liver glycogen stores following a previsuggest that supercompensated glycogen levels can ous exercise session.[32] In addition, some triathletes be achieved without performing a glycogen-depletonly tolerate relatively small amounts of CHO and/ ing exercise bout first and without tapering-down of or fluids during strenuous exercise and hence they the exercise training. This is further supported by may not always be able to consume sufficient work from Fairchild et al.[28] and Bussau et al.[29] In amounts of CHO ‘during’ exercise. Furthermore, in these studies, it was shown that when a short-term some cases, the availability of CHO sources (i.e. high-intensity exercise bout[28] or even complete CHO supplements provided by the race organisers) physical inactivity[29] was followed by a 1-day high may be limited and this can also lead to low CHO CHO intake (~10.5g of CHO/kg BW/day), superintakes. Therefore, ingestion of substantial amounts compensated muscle glycogen stores were attained of CHO (i.e. 200–300g) 3–4 hours before exercise within only 24 hours. This is an important finding as may be an effective strategy to enhance CHO availathis 1-day CHO loading protocol allows triathletes bility during a subsequent exercise bout.[33,34] More to follow their normal training preparations up until importantly, CHO meals or beverages when inthe day prior to competition. Of note, supercompengested 3–4 hours prior to exercise have been shown sated muscle glycogen levels can be maintained for to result in improved endurance capacity.[35,36] at least 3 days when triathletes do not exercise and Therefore, it is recommended for triathletes to conconsume a moderate CHO intake (4–5g of CHO/kg sume a CHO meal or snack (200–300g of CHO) 3–4 BW/day).[30] Thus, if triathletes are not willing or hours before the start of exercise. However, it not able to consume a high-CHO diet the day before should be noted here that triathletes must choose competition, they could start with the 1-day CHO CHO meals that are easily digested and do not cause loading protocol several days before competition GI discomfort during exercise. This is even more  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) Nutritional Considerations in Triathlon 167 important when CHO is consumed shortly before it is unlikely that insulin sensitivity plays an imporexercise (<60 minutes) as there is less time for tant role in the prevalence of rebound hypogly(complete) digestion and absorption of foods. caemia in trained athletes. It may be argued that there are some athletes who are very ‘sensitive’ to 2.1.3 CHO Ingestion <60 Minutes Before Exercise low blood glucose levels and for them exerciseAlthough consumption of high-CHO diets in the induced hypoglycaemia may be a major factor condays before exercise[5] as well as ingestion of CHO tributing to fatigue. These metabolic disturbances meals 3–4 hours prior to exercise[35,36] can have may be attenuated by choosing pre-exercise CHO positive effects on exercise performance, suggessources with a low glycaemic index because these tions have been made that the intake of CHO 30–60 result in more stable blood glucose and insulin reminutes before exercise may adversely affect persponses during subsequent exercise.[44,46,53,59] Anformance.[37,38] Glucose ingestion in the hour before other approach to minimise the glycaemic and insuexercise can result in hyperglycaemia and hyperinlinaemic responses during exercise is to delay CHO sulinaemia, which is often followed by a rapid defeeding until 5–15 minutes before the start of exercline in blood glucose 15–30 minutes after at the cise.[55] Of note, the metabolic and performance onset of exercise,[37,39,40] referred to as rebound effects of CHO ingestion shortly before exercise hypoglycaemia. The fall in blood glucose is most (<15 minutes) are very similar to those observed likely the result of a reduced liver glucose output when CHO is fed during exercise (see section 2.2.1). and an increased muscle glucose uptake.[41] Furthermore, hyperinsulinaemia following glucose inges2.1.4 Fluid Ingestion Before Exercise: Euhydration or Hyperhydration tion inhibits lipolysis and the availability of free fatty acids for oxidation[37,39,40] and this may subseAs discussed in section 1, dehydration can comquently lead to increased muscle glycogen utilisapromise exercise performance and it is, therefore, tion. Hypoglycaemia and depletion of muscle glycoimportant to start exercise in a euhydrated state. gen stores have been associated with the onset of Triathletes are generally recommended to drink fatigue during prolonged exercise. Therefore, preabout 400–600mL of fluid 2 hours before the start of exercise CHO feedings in the hour before exercise exercise.[60] Consuming this amount of fluid promay have the potential to impair performance. Howmotes adequate hydration and allows time for the ever, only two studies have found reduced performexcretion of excess ingested water. Furthermore, it ance capacity,[37,38] while the majority of studies is believed that triathletes who have difficulty drinkreported no change[42-46] or an increased performing sufficient amounts of fluid during exercise or ance[47-51] following pre-exercise CHO ingestion. who lose body water at high rates (i.e. during exerFurthermore, a rebound hypoglycaemia in the early cise in hot conditions), may benefit from hyperhystage of exercise seems to be of little functional dration. Hyperhydration has been suggested to imsignificance as this does not affect exercise performprove thermoregulation and exercise performance, ance.[42,49,52-56] This suggests that there is no need to especially in the heat.[61] The thermoregulatory adavoid CHO intake in the hour before exercise. It is vantages associated with hyperhydration are reinteresting to note here that rebound hypoglycaemia duced increases in core temperature and higher occurs in some triathletes but not in others.[57,58] sweat rates during exercise. Kuipers et al.[58] suggested that the occurrence of Several studies have attempted to induce hyperrebound hypoglycaemia in trained triathletes is rehydration by over-drinking water with or without lated to a high insulin sensitivity. However, we have electrolytes. However, often hyperhydration recently shown that trained individuals who develachieved by over-drinking only produces transient oped rebound hypoglycaemia did not have a higher expansion of body water because most of the fluid insulin sensitivity compared with individuals who overload is rapidly excreted by the kidneys. More did not show rebound hypoglycaemia.[57] Therefore, recently, studies have focused on the use of glycerol  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) 168 Jeukendrup et al. solutions to induce hyperhydrations. Glycerol is a occasions (once in hot conditions and once in warm conditions). The group was split in two with half of naturally occurring metabolite in the human body them receiving glycerol and the other half water. It that is evenly distributed within and between all was found that following glycerol hyperhydration cells at low concentrations (<1 mmol/L).[62] The the increase in completion time between hot and rationale behind glycerol supplementation is due to warm conditions was significantly less than in the its water-binding properties. Typically glycerolplacebo group. Although this study may lack some mediated hyperhydration is performed by ingesting statistical power and there may have been difficul~1 g/kg BW/day of glycerol with or followed by a ties in supplying the triathletes with glycerol in a large volume of fluid (~2L) 1.5–2.5 hours before double-blind fashion, the results seem to indicate exercise.[61,62] It has been shown that in resting conthat glycerol has a protective effect against the negaditions, glycerol-mediated hyperhydration can result tive influences of hot environmental conditions. It in a 400–600mL greater fluid retention than watermust be noted that not all studies found positive mediated hyperhydration. The difference in total effects of glycerol ingestion. For example, Marino et body water content between glyceroland wateral.[64] recently found no difference in 1-hour cycling mediated hyperhydration at rest does not occur until performance in the heat following glycerol inges2–3 hours after glycerol ingestion. tion. Studies that have examined the effects of hyperIt is likely that triathletes who are expecting to hydration on thermoregulation and exercise perbecome severely dehydrated during exercise may formance (in the heat) have produced inconclusive benefit from hyperhydration (glycerol or water). results. This is most likely due to methodological However, triathletes who wish to experiment with differences between studies including variations in glycerol supplementation should be aware of the exercise protocol, environmental conditions, prepotential adverse effects that may be associated with exercise hydration status, and dosage and timing of it, such as headache and GI discomfort.[65] water and/or glycerol supplementation. Recent research that controlled for these confounding vari2.2 During Competition ables has shown that when euhydration is maintained during exercise, pre-exercise hyperhydration 2.2.1 Maintaining CHO Supply During Exercise (water or glycerol) does not further improve thermoIt is has been known for some time that CHO regulation and/or performance.[61] Furthermore, ingestion during exercise improves endurance cathere appears to be no difference in thermoregulapacity by maintaining blood glucose concentrations tion and performance between glyceroland waterand high rates of CHO oxidation.[7,66] Originally, it induced hyperhydration. The advantages of hyperwas believed that CHO feeding could only improve hydration reported in the literature are most likely exercise performance when the exercise was apdue to the fact that by the end of exercise the proximately 2 hours or longer, allowing time for ‘control group’ is more dehydrated. It should be absorption of the CHO. However, more recently, noted that triathletes often do not drink sufficient several studies have demonstrated that even with amounts of fluid to replace sweat losses during exercise as short as 1 hour, CHO intake may have an prolonged exercise and hence they may become advantage.[67-69] In a recent study by Kimber et dehydrated in the early stage of exercise. al.,[70] the average CHO intake during an IronmanOf interest is a recent study by Coutts et al.[63] distance triathlon was 1.0 g/kg BW/hour in female who investigated the effects of glycerol hyperhydratriathletes and 1.1 g/kg BW/hour in male triathletes. tion on Olympic-distance triathlon performance in They achieved these CHO intakes by ingesting very high ambient temperatures. Ten trained triathletes large amounts of CHO during cycling (approximatecompleted a 1500m swim in a 25m pool, a 40km ly 1.5 g/kg BW/hour) with most of the intake during cycle on the road and a 10km run on the road on two the cycling being almost three times as high as  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) Nutritional Considerations in Triathlon 169 during running leg. An interesting observation was g/min by balancing the glucose from the gut and from glycogenolysis/gluconeogenesis. It is possible that in male triathletes the CHO intake during the that when large amounts of glucose are ingested, triathlon was positively correlated with finishing absorption is a limiting factor and the liver will time. Such a relationship could not be demonstrated retain some glucose and will thus act as a second in females. limiting factor to exogenous CHO oxidation. There appear to be some interesting differences Interestingly, recent studies from our laboratory between cycling and running that could be important have shown that a mixture of glucose and sucrose[77] in triathlon. With CHO feeding during cycling, it or glucose and fructose[77] when ingested at a high has repeatedly been shown that muscle glycogen rate (1.8 g/min) leads to peak oxidation rates of breakdown is unaffected.[7,71,72] During running, ~1.2–1.3 g/min and results in ~20–50% higher exhowever, there are suggestions that muscle glycogen ogenous CHO oxidation rates compared with the breakdown is reduced in particular in type I muscle ingestion of an isocaloric amount of glucose. This fibres.[73] Therefore, CHO feeding results in imfinding was attributed to the fact that these CHOs proved performance in cycling and running, alare absorbed, at least in part, by different intestinal though the mechanism by which this occurs may not transport mechanisms and hence there may be less necessarily be the same. This issue is discussed in competition for absorption. A faster rate of intestinal more detail in an excellent review by Tsintzas and CHO absorption might increase the availability of Williams.[74] exogenous CHO in the blood stream for oxidation. It Studies using (stable and radioactive) isotope remains to be investigated whether higher exogemethodology have demonstrated that not all CHOs nous CHO oxidation rates will lead to improved are oxidised at similar rates and hence they may not exercise performance. be equally effective. Glucose, sucrose, maltose, Because exogenous CHO oxidation rates from maltodextrins and amylopectin are oxidised at high single CHOs do not exceed 1.0–1.1 g/min it has rates. Fructose, galactose and amylose have been been recommended to ensure a CHO intake of shown to be oxidised at rates that are generally 60–70 g/hour.[79] A higher CHO intake may result in 25–50% lower. Combinations of multiple transportGI problems, a lower intake may result in a subopable CHO may increase the total CHO absorption[75] timal CHO delivery. It should be noted that during and total exogenous CHO oxidation[76-78] but more exercise in hot conditions slightly less CHO should research is needed. Increasing the CHO intake up to be consumed (50–60 g/hour) as the oxidation of 1.0–1.5 g/min will increase the oxidation rate up to ingested CHO is lower (~10%) in the heat compared about 1.0–1.1 g/min.[79] A further increase of the with a cool environment.[16] intake rate, however, will not further increase the oxidation rates.[79] The most remarkable conclusion 2.2.2 Maintaining Fluid Balance During Exercise that was drawn in a recent review is probably that The prevention of hypohydration during exercise exogenous CHO oxidation rates do not exceed is of prime importance and, in general, triathletes 1.0–1.1 g/min.[79] There is convincing evidence that seem well informed about the dangers. Triathlon this limitation is not at the muscular level but most poses unique nutritional challenges; fluid intake likely located in the intestine or the liver. Intestinal during the swim phase is not possible and fluid perfusion studies seem to suggest that the capacity intake during the run can cause GI problems. In to absorb glucose is only slightly in excess of the addition, swimming and cycling prior to running in observed entrance of glucose into the blood and the triathlon are reported to cause increased oxygen cost rate of absorption may thus be a factor contributing (decreased economy) and larger decreases in body to the limitation. The liver, however, may play an mass and plasma volume compared with the run additional important role, in that it provides glucose alone.[80] Water balance is not only determined by to the bloodstream at a rate of only ~1.0 (or 1.0–1.3) sweat losses but also affected through the saturation  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) 170 Jeukendrup et al. of air in the lungs and through the metabolism of fat Fluids empty from the stomach in an exponential manner[87] with an initial rapid phase of emptying. In and CHO stores in the body. Recently, Rogers et fact, one of the major stimulants of gastric emptying al.[24] attempted to account for all factors involved in is the volume in the stomach, with a positive relawater turnover during an Ironman-distance race and tionship between stomach volume and rate of empreported mean sweat rate to be 940 mL/hour, urinary tying from the stomach.[83,88-90] Rehrer et al.[91] illuslosses at 41 mL/hour and respiratory losses to be 88 trated this by regular repeated ingestion of fluids, the mL/hour. With a volume of water in the region of volume in the stomach is ‘topped up’, therefore, 1.1L being lost every hour, triathletes need to be maintaining the initial rapid rate of fluid delivery to aware of why and how they need to maintain fluid the intestine. In that study, subjects consumed a balance. bolus of fluid before exercising to prime the stomThe cycling section represents the best opportuach before ingesting 150mL every 20 minutes. nity to ingest fluid during a triathlon. During this The absorption of water in the intestine is primastage, fluid is normally most readily available and rily passive, where water passes across the intestinal ingestion is normally least disturbing to performmembrane due to an osmotic gradient.[92] Glucose is ance. Research has indicated that when cycling in actively transported across the intestinal membrane, the heat, performance is improved by ~6% when a a process aided by the inclusion of sodium[93] and it larger volume of fluid was ingested (1330 ± 60 vs has been suggested that water is also co-transported 200 ± 10mL) during exercise prior to the performduring this process.[94] Indeed, isotonic CHO plus ance trial.[68] However, the ingestion of large sodium solutions are absorbed more rapidly than volumes may not always be advisable.[81,82] Gastric either water and/or isotonic sodium-only soluemptying is thought to be negatively affected at tions.[95,96] However, other authors have reported no intensities over 70% V̇O2max. Robinson et additional effect of sodium inclusion on water abal.[82] reported that the maximum rate of intestinal sorption in an already isotonic CHO solution.[97,98] fluid absorption is 0.5 L/hour when cycling at 85% Despite this, the addition of sodium and CHO to peak oxygen consumption (V̇O2peak), an intensity sports drinks is widely recommended to enhance the close to that seen during the cycling sections of absorption of water.[85,99] Olympic-distance triathlons. In the study of RobinHypertonic solutions tend to delay water absorpson et al.[82] subjects consumed ~1.5L of water in 1 tion in the intestine as water instead flows into the hour while cycling at 85% V̇O2peak. It was estimated intestine to dilute the solution before water is abthat ~0.9L remained in the stomach and the intestine sorbed.[85,100,101] Additionally there is contention as at the end of exercise and subjects complained of to whether hypertonic solutions reduce the rate of abdominal fullness, and so clearly the ingestion of gastric emptying, Rehrer et al.[91] found repeated very large volumes may not be advantageous. ingestions of a hypertonic CHO solution resulted in a reduced rate of gastric emptying after 20 minutes Perhaps the best advice is for triathletes to weigh compared with an isotonic solution and consumpthemselves to assess fluid losses during training and tion of a hypertonic beverage during triathlon comracing and limit weight losses to 1% during exercise petition has been related with GI problems.[100] lasting longer than 1.5 hours.[85] In the absence of However, the majority of studies suggest energy such planning, concrete advice is difficult to give as density is considerably more important in determindifferences between individuals, race distances, ing gastric emptying when solutions with an osmocourse profiles and environmental conditions will lality close to those normally found in sports drinks confound any suggestions. However, consuming are used.[90,102,103] 100mL every 10 minutes would provide 600 mL/ hour and would go some way to limiting the effects The importance of beverage taste should not be of dehydration.[86] underestimated. Passe et al.[104] reported that drink  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) Nutritional Considerations in Triathlon 171 acceptability affected voluntary ingestion volumes cells and hence less glucose is available for glycoduring endurance exercise. While this is not surprisgen synthesis in previously exercised muscle.[115] ing, even when offered the CHO drink judged least Therefore, after extensive running, complete recovacceptable in terms of taste, subjects consumed ery of muscle glycogen stores may take longer than more of the flavoured CHO drink than water. In 24 hours despite the intake of a high-CHO diet. addition, it was suggested that perception of drink When CHO intake is adequate (≥7.0 g/kg BW/ acceptability depended on whether the subject was day), co-ingestion of moderate amounts of fat and exercising or resting, underlining the importance of protein do not appear to have an effect on muscle practising race-day strategies during training. glycogen storage during 24 hours of recovery after In summary, a balance must be met between the prolonged exercise.[117] Furthermore, post-exercise goals of maintaining hydration status and providing glycogen storage during the first 24 hours of recovCHO to the working muscle. The rate of fluid abery is not affected by the frequency of food intake as sorption is closely related to the CHO content of the long as the total amount of CHO ingested is suffidrink with high CHO concentrations compromising cient.[118] Practical issues such as appetite and the fluid delivery. The optimum CHO concentrations availability of food may both determine how much seem to be in the range of 5–8% as both fluid and and how often food is consumed, and whether suffiCHO delivery will be high.[105-108] CHO should be cient CHO intake is met in order to replenish glycoingested at a rate of 60–70 g/hour while fluid intake gen stores. CHO foods (and drinks) with a moderate should aim to minimise any weight loss. In all cases, to high glycaemic index are highly recommended a drink should contain sodium (10–30 mmol/L[85,99]) after exercise because they might result in higher for optimal absorption and prevention of hyponaglycogen synthesis rates than low glycaemic index traemia. CHO foods.[119] From the above discussion it can be concluded 2.3 Recovery that the amount of CHO consumed is the most important dietary factor influencing muscle glyco2.3.1 CHO Intake After Exercise gen synthesis. Furthermore, muscle glycogen conMuscle glycogen is of primary importance for centrations can return to pre-exercise values within prolonged endurance exercise and hence the reple24 hours after exercise when sufficient CHO (8–10 tion of glycogen constitutes an important role of the g/kg BW/day) is consumed. Since triathletes seldom post-exercise recovery process. Depending on the compete on two consecutive days there seems to be extent of glycogen depletion and provided that at sufficient time between races for complete recovery least 8g of CHO/kg BW/day is consumed, complete of muscle glycogen stores. Of note, athletes (triathrestoration of these glycogen stores can occur within letes in particular) often train more than once per 24 hours.[109-111] Furthermore, it has been shown that day, and some events require qualification <8 hours when a high-CHO diet (9–10g of CHO/kg BW/day) before the actual event. Although it is unlikely that is consumed between two exercise sessions separatmuscle glycogen stores can be completely resyntheed by a 22.5-hour recovery period, intermittent[112] sised within hours, appropriate nutritional practices and endurance exercise[113] capacity is maintained or can help to optimise the rate of glycogen storage in even improved. It should be noted here that muscle the often limited time available for recovery. Secglycogen synthesis is impaired for several days after tion 2.3.2 summarises nutritional strategies to obtain exercise that causes muscle damage (i.e. eccentric maximal muscle glycogen synthesis rates in the exercise), such as after a marathon.[114-116] Suggesearly hours post-exercise. For more detailed infortions have been made that the impaired muscle mation on this topic the reader is referred to a recent glycogen synthesis following eccentric exercise is due to increased glucose uptake by inflammatory review by Jentjens and Jeukendrup.[120]  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) 172 Jeukendrup et al. 2.3.2 The Early Hours Post-Exercise (<8 Hours) CHO as soon as possible after exercise as this may increase the rate of muscle glycogen storage. The rate of muscle glycogen synthesis in the Studies have found similar rates of muscle glycohours immediately after exercise is largely depengen synthesis after glucose and sucrose ingesdent on the amount and frequency of CHO intake, tion.[126] However, ingestion of an equal amount of the timing of CHO consumption and the type and fructose results in much lower glycogen synthesis form of CHO. Furthermore, suggestions have been rates.[126] This is most probably due to a slower made that the addition of certain protein and/or absorption rate of fructose from the intestine[127,128] amino acids to a CHO supplement can increase the and the fact that fructose requires conversion to rate of muscle glycogen synthesis. The role of proteglucose by the liver before it can be metabolised in in intake for recovery is discussed in section 2.3.3. the skeletal muscle.[128-130] It is recommended to Probably the most important factor determining consume CHO foods with a moderate to high glythe rate of muscle glycogen synthesis is the quantity caemic index because this might result in higher of CHO consumed after exercise. When no CHO is glycogen synthesis rates than ingestion of CHO ingested after exercise, muscle glycogen synthesis foods with a low glycaemic index. Whether the rates are very low. However, very high muscle glyCHO supplement is in solid or liquid form does not cogen synthesis rates are observed when 1.0–1.2g of seem to affect the rate of muscle glycogen syntheCHO/kg BW/hour is ingested at frequent intervals sis.[109,131] CHO beverages are often recommended during a 3to 5-hour recovery period.[121-123] From to triathletes because they also provide a source of the data available in the literature, it seems reasonafluid that may be beneficial for rapid rehydration ble to conclude that maximal glycogen synthesis (see section 2.3.4). Furthermore, when appetite is rates occur at a CHO intake of ~1.2 g/kg BW/hour suppressed immediately after exercise, there may be (or 75–90g of CHO per hour). It should be noted that a preference for drinking fluids rather than eating the highest rates of muscle glycogen synthesis rates solid foods. have been found in studies in which CHO supplements were provided at regular intervals (every 2.3.3 Protein and Amino Acids 15–30 minutes). Thus, in the early hours post-exerSeveral studies have shown that the addition of cise, consumption of small repetitive CHO feedings certain proteins and/or amino acids to a CHO supappears to be more beneficial for high muscle glycoplement can increase muscle glycogen synthesis gen synthesis rates than ingestion of one or two rates by 40–100%, most probably as a result of an larger CHO feedings.[120,123] enhanced insulin response.[123,132] Insulin stimulates The pattern of muscle glycogen synthesis followmuscle glucose uptake and activates glycogen ing glycogen-depleting exercise occurs in a biphasic synthase,[133] the rate-limiting enzyme in glycogen manner. Initially, there is a rapid phase of glycogen synthesis. However, we have recently demonstrated synthesis (insulin-independent phase), which generthat when the total CHO intake is high (1.2 g/kg ally lasts between 30–60 minutes. Following this BW/hour) the presence of a protein-amino acid mixrapid phase of glycogen synthesis, muscle glycogen ture does not further increase the rate of muscle synthesis occurs at a much slower rate (slow phase glycogen synthesis despite a much higher insulin or insulin-dependent phase) and in the presence of response.[121] This suggests that when sufficient CHO availability and high insulin concentrations CHO is consumed (1.2 g/kg BW/hour) there is no this phase can last for several hours.[124] A study by need for protein and/or amino acid ingestion as this Ivy et al.[125] clearly demonstrated that muscle glydoes not lead to higher muscle glycogen synthesis cogen synthesis rates were almost twice as high rates. In addition, most studies have been performed when a CHO supplement was ingested immediately with unpalatable protein hydrolysates and amino post-exercise compared with 2 hours later. It is, acids, which triathletes would not normally contherefore, recommended that triathletes consume a sume. When such protein and amino acids are added  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) Nutritional Considerations in Triathlon 173 to a CHO supplement this might refrain the triathlete water increased urine output and resulted in less from sufficient CHO intake and hence optimal museffective restoration of net fluid balance compared cle glycogen synthesis rates are not reached. with including glucose and electrolytes in the beverIt should be noted that there is some evidence that age.[140] Maughan and Leiper[144] compared the efamino acid ingestion in combination with[134] and fect of either 2, 26, 52 or 100 mmol/L of sodium in without[135] CHO may increase post-exercise protein drinks given after dehydrating exercise. Subjects synthesis and net muscle protein balance (protein were exercised in the heat until they had lost 1.9% of synthesis minus protein degradation).[136] An intheir body mass. After resting for 30 minutes, subcreased protein accretion and an increased availabiljects consumed a volume equivalent to 1.5-times of ity of essential amino acids might contribute to the mass lost over the next 30 minutes. All urine faster tissue growth and repair. Prolonged eccentric produced over the 5.5 hours following drink ingesexercise, such as marathon running or downhill runtion was collected. Urine production was inversely ning, is known to induce severe muscle damage and related to sodium content, the drink with the largest hence nutritional supplements that would speed up amount of sodium resulting the least urine producthe recovery of damaged muscle could be of benefit tion and the greatest net water gain. Only the 56 and to the triathlete. The importance of post-exercise 100 mmol/L drinks resulted in a restoration of amino acid and/or protein ingestion to stimulate net whole-body sodium content, with the 100 mmol/L muscle protein anabolism and the consequence this drink increasing whole-body sodium above premight have on the repair of exercise-induced muscle exercise levels. Plasma volume restoration was also damage remain to be elucidated. related in a similar fashion to beverage sodium concentration. 2.3.4 Restoration of Fluid Balance The mechanism by which sodium exerts a posiThe restoration of fluid balance after exercise is tive effect on net fluid balance during post-exercise an important part of the recovery process and this is rehydration has been proposed to be 2-fold.[145] The even more important following exercise in hot and first effect of sodium is to stimulate glucose absorphumid conditions. It has been suggested that effection in the small intestine as described in section tive rehydration after exercise can only be achieved 2.2.2. The second proposed effect of sodium is to when both sweat loss and the sodium lost in sweat prevent the dilution of plasma sodium that would are replaced.[137] otherwise occur with the ingestion of plain water. Shirreffs et al.[138,139] suggested that at least 150% Low plasma sodium concentrations inhibit the proof the amount of fluid lost during exercise is needed duction of anti-diuretic hormone (ADH, vasopresto ensure complete rehydration. When smaller sin) and result in increased urine volume. Sodiumvolumes of fluid are consumed, equal to sweat containing drinks may also enhance post-exercise losses, optimal rehydration may not be achieved due fluid balance compared with water alone by increasto ongoing urine production. Of note, when the ing the sensation of thirst and, therefore, voluntary sodium content of the drinks is low (23 mmol/L) fluid intake.[142,146] even ingestion of large drink volumes (equal to 1.5While it seems clear that the inclusion of sodium to 2-times the sweat loss) is not adequate to restore prevents plasma sodium dilution and is a positive fluid balance.[139] There seems be an inverse relafactor in post-exercise rehydration, the inclusion of tionship between the sodium content of the ingested potassium does not seem to have a similar effect. fluid and urine production, which suggests that more Sodium is the major ion of the extracellular space fluid is retained when beverages are ingested with a and thus inclusion of sodium in beverages prevents moderate to high sodium content (>50 mmol/L). the plasma sodium dilution that would occur if water Numerous studies have indicated that water is not alone were drunk. Potassium, however, is the major the most effective rehydration beverage.[140-143] Costill and Sparks[140] illustrated that ingestion of plain ion of the intracellular space, and it has been  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) 174 Jeukendrup et al. theorised that inclusion of potassium in a rehydraabove glycogen restoration and hence a more diluted CHO beverage should be consumed. tion beverage might increase the retention of fluid within the intracellular space. Experimental eviThere is some evidence that the ingestion of solid food in combination with plain water may be of dence, however, does not support this hypothesis. additional benefit than ingestion of a similar volume Maughan et al.[147] investigated the effect of glucose of sports drink. In a study of Maughan et al.[150] the alone, potassium alone, sodium alone or all three in volume of fluid in a solid food plus water trial was combination, on rehydration following dehydration equivalent to that in a fluid-only trial but the volume by ~2% from exercise in a hot environment. The of urine produced in the solid-food trial was smaller, addition of either sodium or potassium alone inresulting in improved net fluid balance. However, creased net fluid balance compared with glucose the solid food contained greater sodium and potassialone but there was no further improvement with all um than the sports drink and it is likely that this three in combination. Additional evidence regarding factor was responsible for the differences seen bethe lesser importance of other electrolytes compared tween trials.[145] Fluid retention seems positively with sodium comes from the examination of the related to sodium content of the beverage[144] and it electrolyte concentration of sweat and urine. The may be easier to achieve high intakes of sodium by concentration of potassium, chloride and magnesiconsuming some form of salty solid food after exerum are more dilute in sweat than their concentration cise. in their primary body compartment and, therefore, Although in the majority of cases dehydration tend to become more concentrated due to sweatmay be a problem, there is also a risk of drinking too ing.[148] Costill[148] reported that even repeated days much. Fluid ingested above what is required may of heavy sweating did not result in magnesium or result in GI discomfort or, more seriously, hyponapotassium deficits. In contrast, some researchers traemia.[151-153] These problems will be discussed in have suggested that hypomagnesaemia may be a section 2.4. problem in long-distance triathlon.[149] At present, however, research does not seem to indicate addi2.4 Preventing Nutrition-Related tional benefit of including additional electrolytes Medical Problems other than sodium in rehydration beverages. Probably the most common medical problem in It is clear from the above discussion that sodium triathlon is hyperthermia and heat-related illness. is an important ingredient in rehydration drinks. This can usually be combated by adjusting the However, one disadvantage of beverages that condrinking pattern and strategies to do this have altain high sodium concentrations is that these drinks ready been discussed in sections 2.1.4 and 2.2.2. are not very palatable and this may prevent the There are, however, quite a few other complications triathlete from consuming sufficient amounts of fluthat may be nutrition related such as GI problems, id. Palatability is a major issue when large volumes endotoxaemia and hyponatraemia. These will be of fluid need to be consumed. Therefore, the discussed in sections 2.4.1–2.4.3 of this review. triathlete should choose a rehydration drink that contains sufficient amounts of sodium and does not 2.4.1 Gastrointestinal Problems compromise fluid intake. Addition of moderate There is a very high prevalence of GI complaints amounts of CHO will improve palatability and may during exercise among long-distance runners, triathincrease the rate of intestinal uptake of sodium and letes and athletes involved in other types of strenuwater. However, beverages with high CHO concenous long-lasting exercise.[154-156] The symptoms trations (>10%) will reduce fluid absorption and include dizziness, nausea, stomach or intestinal hence the availability of fluid for rapid rehydration. cramps, vomiting and diarrhoea. Prevalences of When an triathlete is severely dehydrated after exer30–50% have been reported among marathon runcise, the restoration of fluid balance has the priority ners.[157-159] In an attempt to evaluate the prevalence  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) Nutritional Considerations in Triathlon 175 and the nature of the GI symptoms during triathlon, prevalence of symptoms, mild or severe, the aetiology of these GI complaints in endurance athletes is a study was carried out by the French Medical still incompletely understood. Society.[160] The study included 25 640 competitors participating in 101 triathlon events. It was found 2.4.2 Endotoxaemia that 8.9% of the triathletes reported gastric sympIt has been suggested that endotoxaemia may be toms such as nausea, epigastric pain or vomiting, responsible for some of the reported GI problems. and 8% of the competitors reported intestinal Prolonged exercise at high intensities leads to a problems such as diarrhoea or abdominal pain.[160] quantitative redistribution of blood flow. The blood Rehrer et al.[100] reported a link between nutriflow to the exercising muscle is increased (exercise tional practices and GI complaints during a half hyperaemia) in proportion to the energy demand in Ironman-distance triathlon. It was found that GI order to increase the supply of oxygen and subproblems were more likely to occur with the ingesstrates. In addition, during intense exercise the blood tion of fibre, fat, protein and concentrated CHO flow to the skin is increased to facilitate heat dissipasolutions during the triathlon. In particular, bevertion. As a consequence, the blood flow to central ages with very high osmolalities seemed to be retissues (gut and liver) is reduced during exercise by sponsible for some of the reported complaints. almost 80%.[165-167] The blood flow to the gut may Jeukendrup et al.[161] found an even higher prevaeven be further reduced during exercise in the heat lence of symptoms during a long-distance triathlon. when plasma volume may be further reduced.[168] A Thirty triathletes were asked to report their comsimilar redistribution of blood flow is seen in paplaints during swimming, cycling and running and tients with major trauma and/or sepsis and various 92% of them reported at least one complaint during forms of shock. In this situation a serious unone of the disciplines. Severe symptoms included derperfusion of the gut often leads to shock-induced vomiting and diarrhoea and occurred mainly during mucosal damage and invasion of Gram-negative running. It has been suggested that the problems intestinal bacteria and/or their toxic constituents occur especially during running because of the (endotoxins) into the blood circulation.[169] Inmovements of the gut. However, because running is creased circulating lipopolysaccharide (LPS) levels the final event of the triathlon it could also be in patients lead to various symptoms such as fever, because of the duration of the exercise. Peters et shivering, dizziness, nausea, various GI complaints al.[162] investigated this question by adding a cycling such as vomiting and diarrhoea, and ultimately sepleg after the run and still observed more GI sympsis,[170] symptoms similar to those often reported by toms during running compared with cycling. ultra-endurance athletes. Symptoms are often mild and may not even affect Endotoxaemia after strenuous ultra-endurance performance. Some of the symptoms, however, can exercise has been reported. Brock-Utne et al.[171] be very serious and will not only affect performance reported that 81% of 89 ultra-marathon runners in but are also health threatening. For example, marathe Comrades marathon (90km) demonstrated elethon runners and long-distance triathletes occasionvated plasma endotoxin concentrations. Two perally have blood loss in faeces in the hours following cent showed endotoxin (LPS) concentrations >1000 a marathon. Schaub et al.[163] observed epithelial pg/mL, a value reported in patients with meningosurface changes known to occur during ischaemia coccal sepsis and considered to be extremely high if upon colonoscopic inspection of one such triathlete one considers a value of 5 pg/mL the limit for following a marathon and suggested that ischaemia endotoxaemia to predict or exclude oncoming sepof the lower GI tract induced the problems. sis.[172] However, in that study, resting levels of LPS Øktedalen et al.[164] reported increased intestinal also were in the range usually observed in critically permeability after a marathon, indicating damage to ill septic patients. In another study, LPS concentrathe gut and impaired gut function. Despite the high tions increased and the anti-LPS IgG levels marked 2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) 176 Jeukendrup et al. ly decreased after a triathlon (3.2km swim, 140km arises due to loss of sodium in sweat coupled with cycle, 42.2km run).[173] Again, the reported resting very high intakes (8–10L) of water or other lowlevels of LPS were in the range usually observed in sodium drinks.[179] The symptoms of hyponatraemia critically ill septic patients, which raises doubt about are similar to those associated with dehydration and the validity of those results. Other studies utilising include mental confusion, weakness and fainting. subjects with post-exertional illness after a 161km Such symptoms are usually seen at serum sodium (100-mile) cycle ride in the heat[174] and after a concentrations of 126–130 mmol/L. Below 126 marathon[175] showed only minor or no systemic mmol/L, seizures, coma and death may occur. Beendotoxaemia. cause the symptoms of hyponatraemia are so similar Thirty of the triathletes competing in the 1996 to those of dehydration, there can be a danger of Embrun long-distance triathlon volunteered to take misdiagnosis of this condition when it occurs in part in a study investigating the potential relationindividuals participating in endurance races. The ship between endotoxaemia and GI problems. Oneusual treatment for dehydration is administration of third of the triathletes reported stomach problems, fluid both orally and intravenously. If this treatment 21% reported nausea, 7% experienced dizziness, six were to be given to a hyponatraemic individual, the triathletes (21%) vomited and two had diarrhoea.[161] consequences could be fatal. Two triathletes had to abandon the race because of Often, however, triathletes may develop hyponasevere GI distress (vomiting and diarrhoea). Altraemia without displaying the symptoms. Hyponathough there was a high incidence of GI complaints, traemia may occur in a state of euhydration or even including several severe symptoms, only mild endotoxaemia was observed in the athletes investigatdehydration but is generally associated with fluid ed (i.e. LPS just above the 5 pg/mL threshold used to overload.[177] To prevent hyponatraemia, it is recomdefine endotoxaemia). The degree of endotoxaemia mended to avoid overhydration and to inform athwas not related to the incidence or the severity of the letes about the potential dangers of drinking too complaints. The occurrence of endotoxaemia in this much water or sodium-free beverages. Vrijens et study was not related to the fluid or food intake in al.[180] investigated the effect of replacing sweat these athletes.[161] Although there were considerable losses by a sodium-containing drink compared with differences in fluid intake (ranging from 400 mL/ water and found that the sodium-containing drink hour to 1.2 L/hour) and weight loss varied from attenuated the fall in plasma sodium. Interestingly, 0–6kg this also did not seem to be related to the Speedy et al.[181] recently investigated the effects of occurrence of endotoxaemia.[161] sodium ingestion on the development of hyponaIn summary, it seems unlikely that endotoxaemia traemia. Thirty-eight athletes competing in an is responsible for the observed GI problems or the Ironman-distance triathlon were given salt tablets sometimes occurring post-exercise fever, shivering, (700 mg/hour) to ingest during the race. Data coldizziness and nausea, and there is currently no evilected from these athletes were compared with data dence to suggest a link between nutritional practices from athletes not given salt. Sodium ingestion was and endotoxaemia. associated with a decrease in the extent of weight loss during the race. There was no evidence that 2.4.3 Hyponatraemia sodium ingestion significantly influenced changes An electrolyte imbalance, commonly referred to in plasma sodium concentration or plasma volume as ‘water intoxication’ that results from hyponamore than fluid replacement alone in this study. The traemia (low plasma sodium) due to excessive water authors, therefore, suggested that sodium suppleconsumption has occasionally been reported in mentation was not necessary to prevent the developlong-distance triathletes.[153,176-178] This appears to ment of hyponatraemia in these athletes. The be most common among slow competitors in triathletes in this study lost weight, indicating that triathlons and ultra-marathon races and probably  2005 Adis Data Information BV. All rights reserved. Sports Med 2005; 35 (2) Nutritional Considerations in Triathlon 177 4. Romijn JA, Coyle EF, Sidossis LS, et al. Regulation of endogethey had only partially replaced their fluid during nous fat and carbohydrate metabolism in relation to exercise the Ironman triathlon. intensity. Am J Physiol 1993; 265: E380-91 5. Bergström J, Hermansen L, Hultman E, et al. Diet, muscle glycogen and physical performance. Acta Physiol Scand 1967; 3. Conclusions 71: 140-50 6. Hultman E. Physiological role of muscle glycogen in man, with Triathlon is a sport that combines three discispecial reference to exercise. Circ Res 1967; 10: I99-I114 plines (swimming, cycling and running) and compe7. Coyle EF, Coggan AR, Hemmert MK, et al. Muscle glycogen utilization during prolonged strenuous exercise when fed cartitions last between 1 hour 50 minutes (Olympic bohydrate. J Appl Physiol 1986; 61: 165-72 distance) and 14 hours (Ironman distance). The 8. Noakes TD. Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic causes of fatigue in shortversus long-distance performance. Scand J Med Sci Sports 2000; 10: 123-45 triathlons are likely to be different; however, inde9. Coyle EF. Fluid and fuel intake during exercise. J Sports Sci pendent of the distance, dehydration and carbohy2004; 22: 39-55 10. Sawka MN, Pandolf KB. Effects of body water loss in physiodrate depletion are the most likely causes of fatigue logical function and exercise performance. In: Lamb DR, in triathlon. Contrary to traditional beliefs, studies Gisolfi CV, editors. Perspectives in exercise science and sports have demonstrated that it is possible to increase medicine: fluid homeostasis during exercise. Indianapolis (IN): Benchmark Press, 1990: 1-38 muscle glycogen concentrations to very high levels 11. Bentley DJ, Millet GP, Vleck VE, et al. Specific aspects of with minimal modifications in diet and training. contemporary triathlon: implications for physiological analysis and performance. Sports Med 2002; 32: 345-59 Cycling provides the best opportunity to ingest 12. Moseley L, Jeukendrup AE. The reliability of cycling efficienfluids to reduce fluid losses. Based on extensive cy. Med Sci Sports Exerc 2001; 33: 621-7 research, detailed guidelines have been formulated. 13. Sawka MN. Physiological consequences of hypohydration: exercise performance and thermoregulation. Med Sci Sports ExMuch less is known about the causes of gastrointeserc 1992; 24: 657-70 tinal problems that frequently occur, especially in 14. Febbraio MA, Snow RJ, Stathis CG, et al. Effect of heat stress long-distance triathlon. Endotoxaemia has been sugon muscle energy metabolism during exercise. J App Physiol 1994; 77: 2827-31 gested as an explanation for some of the gastrointes15. Fink WJ, Costill DL, Van Handel PJ. Leg muscle metabolism tinal problems, but this has not been confirmed by during exercise in the heat and cold. Eur J App Physiol 1975; recent research. Although mild endotoxaemia may 34: 183-90 16. Jentjens RL, Wagenmakers AJ, Jeukendrup AE. Heat stress occur after an Ironman-distance triathlon, this does increases muscle glycogen use but reduces the oxidation of not seem to be related to the incidence of gastroiningested carbohydrates during exercise. J Appl Physiol 2002; 92: 1562-72 testinal problems. Hyponatraemia has occasionally 17. Pitsiladis YP, Maughan RJ. The effects of exercise and diet been reported and is often associated with very large manipulation on the capacity to perform prolonged exercise in fluid intakes. Future studies should look into the the heat and in the cold in trained humans. J Physiol 1999; 517: 919-30 hazards of dehydration versus hyponatraemia and 18. Gonzales-Alonso J, Teller C, Andersen SL, et al. Influence of guidelines should be formulated that take into acbody temperature on the development of fatigue during procount the potential risk of both dehydration and longed exercise in the heat. J Appl Physiol 1999; 86: 1032-9 19. Nielsen B, Hales JRS, Strange NJ, et al. Human circulatory and hyponatraemia. thermoregulatory adaptations with heat acclimation and exercise in a hot, dry enviroment. J Physiol 1993; 460: 467-85 Acknowledgements 20. Cheuvront SN, Carter III R, Sawka MN. Fluid balance and endurance exercise performance. Curr Sports Med Rep 2003; The research of the authors is funded by Glaxo2: 202-8 21. 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