When an athlete is training for a sport, there are certain nutritional needs that, when met, provide the best performance. A triathlete utilizes both the aerobic and anaerobic systems, so she will use fats as an energy source for the slower, steadier trainings and recovery periods. However, creating adenosine triphosphate (ATP) from fats is a slow process, so much of the race and training will depend on carbohydrates for quick, sustainable energy.
There are three stages to the metabolism of glucose: glycolysis, the Krebs cycle, and oxidative phosphorylation. In glycolysis, glucose enters the cytosol of the cell and is converted into pyruvate. Two ATP molecules are generated per glucose molecule. During this process NAD is converted to NADH and is transported to the mitochondria to be used in the electron transport chain.
In the Krebs cycle, pyruvate formed from glycolysis is transported to the mitochondria where it is converted to acetyl CoA. This process releases two molecules of carbon dioxide and forms two molecules of NADH. Then, FADH2 and NADH are transported to the electron transport chain (SparkNotes, 2012). The Krebs cycle produces two molecules of ATP.
The electron transport chain utilizes NADH-Q reductase, cytochrome reductase, cytochrome oxidase, and oxygen. NADH and FADH2 move down the chain. Each section of the chain harvests bits of energy (SparkNotes, 2012). The electron transport chain produces 26-30 molecules of ATP.
Even though the electron transport chain produces more energy units for the muscles, it takes more time. Also, oxygen limits the ATP generation and rate of the electron transport chain (SparkNotes, 2012). Glycolysis produces energy faster and is the source the body is more likely to use when exercising.
When the athlete is working under oxygen deprivation, as in sprints to the finish or in the beginning of a leg of a triathlon, pyruvate is used to oxidize NADH because oxygen supplies are low. This forms NAD+ and lactic acid. The lactic acid is reformed to pyruvate and reenters the Krebs cycle when more oxygen is available. This will occur during the steady-state legs of the race or during the cool down period.
When the athlete is training or racing, two processes are happening to the muscles. First, protein catabolism occurs when cortisol, catecholamine, and glucagon are breaking down the glycogen and adipose tissue for fuel; this is the break down of the muscle (Insel et al, 2010). This catabolism is what provides the athlete with energy for training or racing. Essentially, this is where the high-energy bond holding together the 3 phosphates in ATP are cleaved to form adenosine diphosphate (ADP), or energy.
Second, protein anabolism is the building up and repair of damaged muscle fibers. Having an adequate supply of carbohydrate and protein before and after a race or training session helps the body stay fueled and repair any damage done by delivering glycogen to damaged muscles (Insel et al, 2010). Essentially, this is where ADP is reformed into ATP for future energy needs. An athlete's body undergoes both these processes daily, and if her nutritional balance is off, then she will feel muscle soreness. A good post-training snack would be a small whole grain bagel, 2 oz of string cheese, and 8 oz of low-fat yogurt (Gruner, 2010). This snack will provide an athlete with the nutritional break down she needs for protein anabolism.
Proper nutrition is important for the athlete's performance, but there is also the timing of the nutrition. Nutritional periodization is a great way to ensure the athlete has adequate carbohydrates, fats, and proteins for maximal performance. There are three phases: preparation, competition, and transition. Each phase is unique in both training and nutrition with specific goals in mind.
The preparation phase is the phase leading up to the competition. This is the phase where the athlete can focus on weight gain or loss, body fat percentage, and hypertrophy (Insel et al, 2010). This is also the phase in which to assess and change habits. During this phase, the athlete should be consuming 5-12+ g/kg carbohydrates, 0.8 g/kg fats, and 1.2-1.7 g/kg protein. For my athlete, who weighs 67.5 kg, that means she should consume around 340 g carbohydrate, 55 g fats, and 83 g protein during this phase.
The competition phase is where the athlete works on improving speed and strength. This is also the phase where she establishes her eating routing, maintains her weight, and works on recovery (Insel et al, 2010). During the race phase, the athlete should consume 7-19 g/kg carbohydrates, 0.8-3.0 g/kg fats, and 1.4-2.0 g/kg protein. This increases my athlete's consumption to about 810 g carbohydrates, 100 g fats, and 120 g protein.
The transition phase is the off-season phase. This is the phase where the athlete focuses on good nutrition, calorie control, and experimenting with different types of food (Insel et al, 2010). During this phase, the athlete consumes 5-6 g/kg of carbohydrates, 0.8-1.0 g/kg fats, and 1.2-1.4 g/kg protein. This puts my athlete at approximately 337 g carbohydrates, 54 g fats, and 81 g protein.
Nutritional timing is also important for the athlete's performance. An athlete needs to fuel and refuel before, during, and after training or a race. It is important that the carbohydrates be complex carbohydrates with minimal sugars, avoid saturated fats, and choose lean proteins.
The athlete should consume carbohydrates 2-4 hours before exercise to replenish glycogen stores. This helps the athlete's endurance levels. This meal should contain 10-15% total calories in protein and less than 20% total calories from fat (Insel et al, 2010). The athlete can then have a high-carb snack with fluids 30 minutes before a race or training if it does not upset her system (Gruner, 2010).
During and event or training, the athlete needs to hydrate. The longer events, like full triathlons or iron man triathlons, may require the athlete to replenish carbohydrates during the race as well. This can be done with sports drinks, gels, or water with juice. The best combination for the athlete will be determined during the preparation phase.
After training or a race, it is important for the athlete to replenish carbohydrate stores. One way is to consume 1-1.5 g of carbohydrate/kg of body weight within 30 minutes and another 1-15 g of carbohydrate/kg of body weight 2 hours post exercise (Insel et al, 2010). It is important to eat protein with the carbohydrate for increased glycogen synthesis and more protein synthesis (Insel et al, 2010).
As can be seen, quite a bit happens during training and racing. Providing the athlete with proper amounts of carbohydrates, fats, and proteins before the race or training session will help her body build up the stores of glycogen it needs for sustained energy. Providing endurance training during the preparation phase will help train her body to utilize fat stores in the adipose during longer training sessions and longer race distances, as well as helping with recover. Providing the proper mix of carbohydrates, fats, and proteins after the training session or race will help her recover and repair faster so she will be ready for the next session. Much of the breakdown of amounts and types of foods will be determined during the recovery phase so she will be ready to focus on performance during the preparation and race phases.
References:
Gruner, Mandy (2010) Diet of an Athlete. Retrieved on April 2, 2012, from www.livestrong.com/article/140112-diet-athlete/
Insel, Paul; Turner, R. Elaine; Ross, Don (2010) Discovering Nutrition, 3rd Edition Jones & Bartlett
SparkNotes (2012) Carbohydrates. Retrieved on April 2, 2012, from www.sparknotes.com/health/carbohydrates/section3.html
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