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What is a consequence of low energy availability in an athlete?
Where is endogenous carbohydrate stored?
What is the maximum rate of exogenous carbohydrate oxidation during exercise?
What form of carbohydrate is most ergogenic during endurance exercise?
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What is the recommended rate of carbohydrate consumption during prolonged exercise?
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What strategy can facilitate low muscle glycogen availability during an endurance training session?
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At what percentage of VO2max does the maximal rate of fat oxidation occur?
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What is a benefit of consuming multiple sources of carbohydrate during exercise?
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What is the primary purpose of carbohydrate consumption in an athlete's pre-event meal?
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What percentage of VO2 max is associated with maximal fat oxidation during exercise?
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What is the outcome of each cycle of beta-oxidation in ATP production?
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What is the primary mechanism of fatty acid mobilization from adipose tissue during exercise?
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Why is it important to consume a meal low in fibre before an athletic event?
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What is the primary role of sodium in an athlete's pre-event meal?
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What is the maximum rate of exogenous carbohydrate oxidation during exercise?
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Why is it important for athletes to periodize their energy intake?
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What is the consequence of consuming excessive fluid for athletes?
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How long can endogenous carbohydrate fuel high intensity endurance exercise?
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What is the purpose of managing fluid intake for athletes?
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Why is it important for athletes to consume carbohydrates during exercise?
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What is the source of energy for working muscles during exercise?
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How do athletes determine their vitamin requirements?
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Study Notes
Pre-Event Meal Characteristics
- Optimal pre-event meal for an athlete should contain 1-4g/kg of carbohydrates to top up muscle glycogen.
- It should be high in sodium to assist with fluid retention and low in fiber for gastrointestinal comfort.
Intensity of Exercise for Maximal Fat Oxidation
- Fat oxidation occurs at an intensity of 45-65% VO2 max, but there is significant individual variation.
ATP Production from Beta-Oxidation
- Fatty acetyl-CoA molecules pass through a sequence of four enzymatically catalyzed reactions in one cycle of beta-oxidation.
- Each cycle produces one acetyl-CoA, one FADH, and one NADH.
- Acetyl-CoA enters the Krebs cycle to generate ATP, while FADH and NADH enter the electron transport chain to generate ATP.
Fatty Acid Mobilization from Adipose Tissue
- Fatty acids are mobilized from adipose tissue during exercise.
Low Energy Availability
- An athlete with low energy availability may have impaired bodily functions and impaired performances across any timeframe.
Endogenous and Exogenous CHO Use During Exercise
- Endogenous carbohydrate is stored in the muscle and liver.
- Glycogen stored in the muscle can be used directly for energy during exercise.
- Liver glycogen must be converted to glucose and then transported in the blood to the working muscles for use during exercise.
- Endogenous carbohydrate can fuel high-intensity endurance exercise for around 2-3 hours before stores become depleted.
- Exogenous carbohydrate can be used to provide energy during exercise when ingested in solid, liquid, or gel forms.
- The maximal rate of exogenous carbohydrate oxidation during exercise is approximately 1.8g/min.
Ergogenic Forms of CHO During Endurance Exercise
- Gel is the most ergogenic form during endurance exercise.
Carbohydrate Consumption During Prolonged Exercise
- 60-90g/hr of CHO should be ingested during prolonged exercise lasting 2-3 hours or more.
- These should come from multiple sources of CHO (e.g., mix of glucose and fructose).
Strategies for Low Muscle Glycogen Availability
- Training twice a day, training after an overnight fast, and consuming a low carbohydrate diet can facilitate low muscle glycogen availability during an endurance training session.
Maximal Rate of Fat Oxidation
- The maximal rate of fat oxidation occurs at approximately 46-65% of VO2max.
Energy Intake and Training Demands
- Energy intake should not be static and will ideally change on a daily basis to meet variable energy requirements associated with fluctuating training demands.
Fluid Intake and Over-Hydration
- Athletes should manage their fluid intake cautiously to prevent over-hydration if they are competing in cooler environments, slower to finish a race or event, have a smaller body size, and knowingly have many opportunities or access to drink during the event.
Vitamin Requirements for Athletes
- Nutrient reference values for vitamin requirements are used as a starting point for athletes, but there are no definitive recommendations established.
Excessive Fluid Consumption and Performance
- Athletes who consume excessive fluid to their requirements are more likely to experience a weight increase, bladder and GI discomfort, which may be detrimental to performance.
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Quiz on optimal pre-event meal for athletes and exercise intensity for maximal fat oxidation.
