IB Sports, exercise and health science A.2.2.2 Nutritional Strategies for Exercise and the Effects of Low Energy Availability Notes

Nutrition Strategies

Pre-Exercise Nutrition Strategies

1. Pre-exercise nutrition plays a critical role in enhancing performance during both endurance and high-intensity activities.
2. Proper fueling before exercise helps optimise energy availability, delay fatigue, and enhance recovery.

Carbohydrate Loading

1. Carbohydrate loading enhances endurance performance by ensuring sufficient energy is available for prolonged physical activity.
2. Glycogen is stored in muscles and liver and is the primary fuel used during aerobic activity.
3. By carbohydrate loading, athletes can increase their glycogen stores beyond normal levels.
4. A well-conducted loading protocol ensures a maximal glycogen reserve, helping prevent early fatigue and maintaining energy levels throughout the event.

Phases of Carbohydrate Loading

1. Depletion Phase: Involves a reduction in carbohydrate intake and intense exercise (usually about 3-4 days before the event) to deplete glycogen stores.
2. Loading Phase: A high-carbohydrate diet (typically 7-12 g per kg body mass per day) over 24-72 hours combined with reduced training drives supercompensation of glycogen stores.

Glycogen Depletion in Different Fibre Types

1. Slow-twitch (type I) fibres: Dominant at low-to-moderate intensities. Deplete first during long endurance work.
2. Fast-twitch (type II) fibres: Recruited as intensity rises. Emptied quickly by all-out anaerobic efforts.
3. Specificity rule: ~30 seconds of maximal cycling can substantially reduce fast-twitch glycogen even though slow-twitch may remain full.

Timing and Composition

1. The timing and composition of your pre-exercise meal can affect energy levels, glycogen availability, and overall performance.
2. The type of carbohydrate consumed, whether low or high GI, can also affect energy release during exercise.

Low GI vs High GI Carbohydrates

1. Low-GI Carbohydrates (e.g., whole grains, fruits) are digested more slowly and provide a steady release of glucose, helping to sustain energy levels during prolonged exercise.
2. High-GI Carbohydrates (e.g., white bread, potatoes, sugary foods) are rapidly digested and cause a quick spike in blood glucose and insulin, providing immediate energy for short bursts of intense exercise.

Glycemic Index (GI) for Recovery

1. Ranks foods by how fast 50 g of their carbohydrate raises blood glucose, with pure glucose set at 100.
2. High-GI foods: Sugary drinks, white rice, sports bars. Best choice for rapid post-exercise recovery when another session is within 24 hours.
3. Low-GI foods: High-fibre cereals, peanuts, raw fruit and vegetables. Better for sustained pre-exercise meals.

Timing

1. Ideally, a pre-exercise meal should be consumed 2-3 hours before exercise to allow time for digestion.
2. A meal high in carbohydrates, moderate in protein, and low in fat helps provide adequate fuel without causing digestive discomfort.
3. If eating closer to exercise (30 minutes to 1 hour), focus on high-GI carbohydrates for a quick energy boost.

Daily Protein Requirements

1. Healthy adult baseline: 0.8 g protein per kg body mass per day.
2. Endurance athletes: 1.2-1.4 g per kg per day to repair muscle and connective tissue and replace amino acids oxidised during long sessions.
3. Strength athletes: 1.2-1.7 g per kg per day to support muscle hypertrophy.
4. Growing children, recovering patients, breastfeeding mothers: Elevated intake to support tissue growth or repair.
5. No storage form: Protein is not stored in the body. A daily intake is required because the amino acid pool is constantly broken down and rebuilt.

Role of Protein in Pre-Exercise Nutrition

1. Pre-exercise protein intake helps ensure that amino acids are available for muscle repair and reduces muscle breakdown during prolonged or high-intensity activities.
2. While protein is not the primary fuel source during exercise, it helps to reduce muscle damage and accelerate recovery post-exercise.

Nutrition During Exercise

During exercise, nutritional priorities shift to hydration, electrolyte replacement, and carbohydrate replenishment to maintain performance and endurance.

Hydration and Electrolyte Replacement

1. Fluid loss during exercise (due to sweating) can result in dehydration, leading to reduced performance, muscle cramping, heat exhaustion, and fatigue.
2. Sports drinks containing sodium, potassium, and other electrolytes are recommended for exercise durations longer than 1 hour to ensure proper hydration and prevent cramping.

Carbohydrate Replenishment

1. Carbohydrate replenishment is crucial for maintaining blood glucose levels and ensuring continued energy during exercise, especially in endurance sports.
2. Muscle glycogen stores are sufficient for about 90-120 minutes of continuous exercise before depletion forces a drop in intensity ('hitting the wall').
3. Sports drinks, glucose gels, and energy bars are commonly used for carbohydrate replenishment during exercise.
4. The goal is to consume 30-60 g of carbohydrates per hour during exercise lasting longer than 1 hour to maintain blood glucose levels and delay glycogen depletion.
5. Consuming carbohydrates in the form of glucose or fructose (or a combination of both) helps maximise absorption rates.

Carbohydrate Timing Across an Event

1. Before exercise: Low-to-moderate GI carbohydrate 2-3 hours before to top up liver glycogen. Avoid heavy fat, fibre, or protein right before the session.
2. During exercise: In events longer than ~1 hour, 30-60 g carbohydrate per hour (sports drinks, gels, bars) sustains blood glucose and delays glycogen depletion.
3. After exercise: High-GI carbohydrate immediately after a session refills muscle glycogen fastest, especially important when the next session is later the same day. Adding protein supports tissue repair.

LEA and RED-S

Low Energy Availability (LEA)

1. LEA occurs when an individual's caloric intake is insufficient to meet the energy demands required for bodily functions, including daily activities and exercise.
2. LEA can be caused by several factors such as inadequate nutrition, high physical activity levels without compensating caloric intake, or an imbalance in energy expenditure and intake.
3. Consistently low energy availability leaves the body without enough energy for essential physiological functions. This affects both health and performance.

Energy Availability (EA) Formula

1. Formula: EA = (dietary energy intake − exercise energy expenditure) ÷ fat-free mass (FFM).
2. Healthy threshold (biological females): ~45 kcal/kg FFM/day supports normal physiological function.
3. LEA threshold (biological females): Below 30 kcal/kg FFM/day.
4. Optimal threshold for biological males: Less clearly defined. Signs include low testosterone, mood changes, and frequent illness.
5. EA after exercise: Represents the energy left over to power thermoregulation, growth, and immune defence.

Relative Energy Deficiency in Sport (RED-S)

1. RED-S is the long-term physiological consequence of prolonged LEA, not a separate condition.
2. It negatively impacts various physiological systems, particularly hormonal balance, bone health, and performance.
3. RED-S is typically seen in sports requiring low body weight or high endurance, such as gymnastics, long-distance running, and figure skating.
4. It can also occur in athletes under extreme pressure to lose weight or maintain a specific body composition.

Sports at Highest Risk

1. High-risk disciplines: Track and field, cross-country running, cycling, wrestling, gymnastics, rowing, and synchronised swimming. Anywhere a high power-to-mass ratio or extreme leanness is rewarded.
2. Not sex-specific: Most early research focused on biological females. There is still a gap in understanding RED-S in biological males. Low testosterone, mood changes, and frequent illness can all signal LEA in male athletes.

Consequences of RED-S

1. Reduced metabolic rate: Resting energy expenditure drops as the body protects itself.
2. Disrupted menstrual function: Irregular or missing periods in biological females. Lower testosterone in biological males.
3. Compromised bone health: Reduced bone mineral density and raised stress fracture risk.
4. Weakened immunity: More frequent upper respiratory tract infections.
5. Reduced protein synthesis: Slower muscle repair and adaptation; raised injury risk.
6. Cardiovascular changes: Reduced training adaptations and lower resting cardiovascular function.

Effects of LEA and RED-S

Decreased Bone Density

1. One of the most significant long-term consequences of RED-S is the reduction in bone density.
2. Low energy availability disrupts the body's ability to regulate bone resorption and formation, making bones more fragile and increasing the risk of stress fractures.
3. Insufficient caloric intake leads to lower levels of estrogen (in females) and testosterone (in males), both of which play a crucial role in maintaining bone health.

Hormonal Imbalances

1. LEA and RED-S cause disruptions in several key hormones, particularly those involved in metabolism and reproduction.
2. In women, this can lead to menstrual dysfunction, such as amenorrhea (absence of menstruation), while in men, low testosterone levels may occur.
3. These hormonal imbalances impact not just reproductive health, but also metabolic functions, mood regulation, and overall health.

Reduced Performance

1. The primary concern for athletes with LEA or RED-S is reduced performance.
2. The body does not have the necessary energy to fuel exercise and recovery, leading to fatigue, decreased endurance, slower reaction times, and impaired recovery.
3. Athletes may struggle to complete workouts at the required intensity, experience delayed recovery, and have an increased risk of injury due to the body's compromised ability to repair tissues.