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Nutrition and Performance in Sport

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Christophe Hausswirth

Chapter 4. Nutrition and specific sport populations

Topic 2. Fluid and food intake strategies of Olympic distance elite triathletes

Gregory R Cox

Résumé

Triathletes face a range of obstacles in meeting nutrient and fluid requirements due to daily training commitments. Residual fatigue from training, reduced appetite following intense training sessions, inadequate planning and lack of access to appropriate foods and fluids make it difficult for time-poor triathletes to meet the added energy, nutrient and fluid demands associated with heavy daily training. The relative importance of managing body mass and body composition for a triathlete is influenced by the level at which the athlete competes and the specific triathlon distance raced. In a study investigating the kinanthropometric features of elite-level Olympic-distance triathletes, researchers found that slower total race times and run times were related to increasing levels of adiposity (Landers, Blanksby et al. 2000).
Given the importance of body mass and body composition management, dietary advice aimed at enhancing daily training performance and promoting recovery between training sessions should be modified accordingly. A varied diet, focused on nutrient-rich foods and fluids that is adjusted in response to daily training loads, may assist athletes in avoiding extreme dietary behaviours such as severe energy restriction, reduced variety of foods and use of strict dietary rules previously observed in triathletes. Triathletes express a keen interest in the benefits of optimizing their dietary intakes to enhance exercise performance, with many knowledgeable about nutrition. Accompanying this interest and knowledge, is a heightened awareness and use of dietary supplements and nutritional ergogenic aids.
Fluid intake advice to triathletes should consider issues that directly impact hourly sweat losses (i.e. intensity of exercise, environmental conditions, and gender), the opportunities for fluid intake as well as the athlete’s tolerance of fluid intake. Developing an individualized fluid intake strategy for Olympic-distance triathletes provides the added benefit of managing total carbohydrate intake.

Texte intégral

1. Daily training nutrition issues

1A fundamental difference in the dietary intake between an elite endurance athlete and their sedentary counterparts is that endurance athletes must consume adequate energy and carbohydrate to meet the demands of intense training and competition (Tarnopolsky, Gibala et al. 2005). Endurance athletes undertake extended and/or multiple exercise sessions each day. For example, triathletes have been reported to train 20 hours per week, with some elite competitors training as much as 40 hours a week during periods of intense conditioning (Gulbin and Gaffney, 1999). A primary consideration for endurance athletes is to ensure muscle glycogen stores are adequately restored on a daily basis to support the daily demands of training (Burke, Kiens et al. 2004). Since the quantity of carbohydrate consumed between training sessions is the primary factor in restoring muscle glycogen stores (Jeukendrup, Jentjens et al. 2005), adopting a dietary framework whereby daily carbohydrate intake is manipulated to reflect the fuel cost of daily training will ensure appropriate glycogen repletion (Broad and Cox, 2008).

2Recently, experts have refined dietary prescriptions regarding daily refuelling to encourage athletes to achieve a carbohydrate intake that is aligned to the specific fuel requirements of their training sessions and glycogen restoration needs (Burke, Kiens et al. 2004). Current guidelines specify various carbohydrate intake ranges, based on daily exercise patterns and expressed relative to an athlete’s body mass (see Table 1). Interpretation of these guidelines into individual dietary prescription should consider the athlete’s overall daily energy requirements, specific training volume and intensity, and requirements for growth and development (for children and adolescent athletes). Furthermore, they should be fine-tuned according to the feedback from training outcomes and other nutrition goals.

Table 1: Guidelines for carbohydrate intakes in everyday training (adapted from Burke and Cox [Burke and Cox, 2010]).

Activity

Carbohydrate targets (g.kg-1.d-1)

Daily needs for fuel and recovery*

Light training programme (low intensity or skill-based exercise)

3 to 5

Moderate exercise programme (i.e. ~1 h per day)

5 to 7

Endurance programme (i.e. 1 to 3 h per day of moderate- to high-intensity exercise)

6 to 10

Extreme exercise (i.e. > 4 to 5 h per day of moderate- to high-intensity exercise)

10 to 12

Special situations for requiring fuel

Speedy refuelling
Less than 8 h recovery between two demanding workouts

1 to 1.2 g.kg-1 immediately after first session Repeated each hour until the normal meal schedule is resumed

* Note that large athletes and athletes undertaking a weight-loss programme may be better suited to reduce their fuel intake to the needs of the previous category

3Given the importance of body mass and body composition management for endurance athletes, dietary advice aimed at enhancing daily training performance and promoting recovery between training sessions should be modified accordingly. For instance, in a study investigating the kinanthropometric features of elite-level Olympic-distance triathletes, researchers found that slower total race times and run times were related to increasing levels of adiposity (Landers, Blanksby et al. 2000).

4While many athletes focus solely on strategies that will assist in reducing body fat levels, they should be reminded to implement strategies that promote lean muscle accretion. This is particularly relevant to younger triathletes transitioning into elite-level competition as a high power-to-weight ratio offers a physical advantage on the cycle and run legs. Based on current evidence it would seem that 20 to 30 g of protein consumed immediately post-resistance exercise will optimize muscle protein synthesis (Moore, Robinson et al. 2009). Furthermore, a fast-acting protein such as whey seems to offer an advantage over other proteins, at least in the post-workout period (Tang and Phillips, 2009).

5It’s important to ensure a meal plan developed for triathletes with large daily fluctuations in energy expenditure can be easily manipulated by the athlete to compensate for changes in daily exercise patterns. Additional energy (namely in the form of carbohydrate) can be included before, during or after training to support daily exercise performance and recovery between exercise sessions (Figure 1). A varied diet, focused on nutrient-rich foods and fluids and that is adjusted in response to daily training loads, may assist athletes in avoiding extreme dietary behaviours such as severe energy restriction, reduced variety of foods and use of strict dietary rules previously observed in triathletes (DiGioacchino DeBate, Wethington et al. 2002). A high-quality protein source should be included at each scheduled meal, as well as strategically incorporated into the post-exercise recovery snack. It should be noted that triathletes have a heightened awareness and use of dietary supplements and nutritional ergogenic aids, which must be managed by the sports nutrition professional (Worme, Doubt et al. 1990).

Figure 1: An example meal plan for an elite female triathlete.

Figure 1: An example meal plan for an elite female triathlete.

2. Competition nutrition issues

6Current dietary guidelines for an acute exercise bout (e.g. competition) encourage athletes who participate in events lasting longer than 60 to 90 min practise strategies that optimize carbohydrate availability throughout the duration of the exercise (Burke, Kiens et al. 2004). Acute intervention studies involving protocols of endurance exercise clearly demonstrate that exercise capacity and performance are improved when pre-exercise muscle glycogen stores are elevated by undertaking a carbohydrate-loading regimen in the final two to three days prior to exercise (for review see (Hawley, Schabort et al. 1997)). Furthermore, incorporating a pre-exercise meal and consuming carbohydrate during endurance exercise also improve exercise capacity and performance (Stellingwerff and Cox, 2014; Hargreaves, Hawley et al. 2004).

7The primary purpose of feeding carbohydrate during continuous strenuous exercise is to maintain blood glucose concentration and carbohydrate oxidation in the latter stages of prolonged exercise (Coggan and Coyle, 1987). Higher blood glucose and insulin levels and lower plasma free fatty acids are consistently reported in subjects fed carbohydrate during exercise compared to a carbohydrate-free placebo (Coyle, Hagberg et al. 1983). Peak rates of exogenous carbohydrate (i.e. carbohydrate consumed) in the form of single transportable carbohydrate appear to be ˜1.1 g.min-1 (Jentjens, Venables et al. 2004). Adopo et al (1994) were the first to report that a beverage containing multiple carbohydrate sources was oxidized at a higher rate than a single transportable carbohydrate. In a series of related studies (Jeukendrup, 2010), ingestion of multiple transportable carbohydrates (i.e. glucose + fructose) increases peak oxidation rates of exogenous carbohydrate to as much as 1.75 g.min-1. The available evidence suggests that exogenous carbohydrate oxidation (namely glucose) is most likely limited by the rate of absorption from the small intestine into the systemic circulation (Shi, Summers et al. 1995).

8The beneficial effect of consuming carbohydrate throughout endurance exercise (> 90 min duration) is a consistent and reproducible finding [for review see: (Stellingwerff and Cox, 2014)]; furthermore, it is possibly a more effective strategy than consuming carbohydrate before exercise (Febbraio, Chiu et al. 2000). The amount of carbohydrate associated with performance benefits seems to vary according to the duration of exercise, which also suggests that several mechanisms may be responsible for the performance enhancement (Karelis, Smith et al. 2010; Stellingwerff and Cox, 2014). Demonstrating the high end of the spectrum of fuel intake during exercise (Currell and Jeukendrup, 2008), subjects ingesting a glucose and fructose beverage in a 2:1 ratio (1.8 g.min-1) completed an endurance cycling protocol 8% faster than when ingesting a glucose-only beverage (1.8 g.min-1) and 19% faster than when ingesting water alone. Although not directly assessed, researchers speculate that the improved performance observed in the glucose and fructose trial was due to a sparing of endogenous carbohydrate sources (Currell and Jeukendrup, 2008).

9At the other end of the spectrum, studies in runners and cyclists undertaking exercise tasks lasting ˜60 minutes have also found improved performance when smaller amounts of carbohydrate are fed during exercise, including amounts as little as mouth rinsing with carbohydrate-containing fluid [for review see: (Rollo and Williams, 2011)]. The underlying mechanism for improved performance in this type of activity remains unclear, although is likely to involve an increase in central drive or motivation (Chambers, Bridge et al. 2009).

10We recently demonstrated that it was common practice for triathletes to consume a substantial amount of carbohydrate (197 ± 73 g) before the start of an Olympic-distance triathlon (ODT), with races that started later in the day providing greater opportunity to consume carbohydrate (Cox, Snow et al. 2010). Athletes consumed 24% more carbohydrate when commencing a race after mid-day (1.00-1.30pm) compared to a late morning (11.00-11.15am) race start. Although the triathletes regularly consumed sports drink and sports gels during the race, average hourly carbohydrate intakes (˜25 g and ˜23 g for men and women, respectively) fell below suggested carbohydrate intakes for endurance exercise lasting approximately two hours (Stellingwerff and Cox, 2014). Of interest, higher intakes of carbohydrate were observed in warm weather conditions compared to mild weather conditions (˜25 g versus ˜20 g), as athletes consumed more carbohydrate from carbohydrate-containing drinks (Cox, Snow et al. 2010).

11Lower overall rates of carbohydrate ingestion observed in our study likely reflect the limited time available for drinking and eating during an ODT race especially when race tactics require concentration and bike-handling skills (Jeukendrup, Jentjens et al. 2005). To complicate the issue, athletes have reduced gastrointestinal tolerance at higher intensities of exercise (Bentley, Cox et al. 2008). As a counter to the potentially reduced opportunities for intake of fluid and food while cycling or running, there is now a range of sports products and devices allow for greater carbohydrate intakes. For example, the development of carbohydrate gels and sports confectionery products and special packaging allows more practical access to a range of products. Indeed, in ultra-endurance triathlon events (i.e. Ironman triathlon) where athletes have greater opportunity and better tolerance for food and fluid intake, higher carbohydrate intakes during the event (82 ± 15 g.h-1 and 62 ± 19 g.h-1 for men and women, respectively) have been reported (Kimber, Ross et al. 2002). Whether it is beneficial to consume higher carbohydrate intakes during an ODT event than observed among the subjects in our study is unclear. While drafting during the cycle leg in a modern day ODT results in a significant metabolic saving compared to cycling alone (Hausswirth, Lehenaff et al. 1999), the intermittent nature of the cycling leg during an ODT increases blood glucose oxidation (Palmer, Borghouts et al. 1999).

12Fluid intake guidelines for athletes competing in endurance events such as triathlon should reflect the unique circumstances and specific challenges athletes face. Recent guidelines for the consumption of fluid during exercise state that “the goal of drinking during exercise is to prevent excessive dehydration (> 2% body weight loss) and excessive changes in electrolyte balance from compromising performance and health” (Sawka, Burke et al. 2007). Failure to follow these guidelines may lead to voluntary dehydration, rises in core temperature, and the potential for the development of a life-threatening heat injury (Convertino, Armstrong et al. 1996).

13Interestingly, in ultra-endurance events (such as Ironman triathlon) where the intensity of exercise is reduced and there is ample opportunity for fluid intake, drinking to levels that balance body mass losses may increase the risk of developing hyponatraemic encephalopathy (Hew-Butler, Verbalis et al. 2006). Therefore, to avoid the deleterious effects of drinking too much or too little during exercise, triathletes should develop an individualized fluid intake plan for competition based on previous fluid balance observations in training. Developing an individualized fluid intake plan provides the added benefit of allowing an athlete to plan their carbohydrate intake, particularly if they plan on consuming carbohydrate containing beverages throughout a race. When assessing fluid balance (based on changes in body mass) in endurance events, an allowance should be made for metabolic fuel losses (Speedy, Noakes et al. 2001) as well as pre-exercise hydration status. The timing of fluid consumed may be an important consideration for triathletes competing in Olympic-distance triathlon events as a recent study demonstrated that athletes had faster run times when fluid was consumed early during the cycle leg of a simulated triathlon event (McMurray, Williams et al. 2006).

Bibliographie

3. Bibliographic references

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Table des illustrations

Titre Figure 1: An example meal plan for an elite female triathlete.
URL http://books.openedition.org/insep/docannexe/image/1862/img-1.jpg
Fichier image/jpeg, 148k

Auteur

PhD, Department of Sports Nutrition Australian Institute of Sport (AIS) Canberra, Australia. E-mail: greg.cox@ausport.gov.au

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