Sports Nutrition and Exercise Intensity

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.