IB Sports, exercise and health science B.1.3.3 Energy Supply and Nutritional Factors in Muscular Contraction Notes

ATP provides immediate energy for muscular contraction

1. An ATP molecule is made of an adenosine unit and three phosphate groups linked by high-energy bonds.
2. When the bond between the second and third phosphate is broken in hydrolysis, energy is released and the molecule becomes ADP and a free phosphate (Pi).
3. A typical adult produces and uses around their own body weight in ATP each day, because ADP is recycled back into ATP almost as fast as it is used.
4. Muscle contractions require energy, which is supplied by adenosine triphosphate (ATP).
5. ATP is broken down within the muscle cells to release energy, enabling the interaction between the proteins actin and myosin that drive contraction.
6. ATP supply must be continuously regenerated because muscle stores are limited.
7. ATP is generated through three primary energy systems:
   1. Phosphagen System (ATP-PC system): Immediate energy for short bursts of activity.
   2. Anaerobic Glycolysis (Lactic Acid System): Energy for moderate-duration, high-intensity activities.
   3. Aerobic System: Sustained energy for long-duration, endurance-based activities.

ATP-PC system powers explosive efforts

1. The ATP-PC system uses phosphocreatine (PCr) stored in the muscle to rebuild ATP from ADP almost instantly.
2. No oxygen is involved and no waste product is produced.
3. PCr stores are small, so the system fuels maximum effort for about 8 to 10 seconds.
4. The ATP-PC system dominates a 100 m sprint, a vertical jump, a single weightlifting attempt, or a tennis serve.
5. PCr stores recover about 70% in 30 seconds and fully in 3 to 5 minutes.

Anaerobic glycolysis bridges the gap

1. Anaerobic glycolysis breaks down glucose without oxygen, generating ATP quickly and producing lactate.
2. The system runs for about 10 seconds to 2 minutes at high intensity.
3. Anaerobic glycolysis dominates a 400 m or 800 m race, a high-intensity interval, or repeated 30-second sprint efforts.
4. Accumulating hydrogen ions lower the muscle's pH and contribute to fatigue.

The aerobic system sustains long-duration activity

1. The aerobic system uses oxygen to break down carbohydrate and fat into ATP.
2. It produces ATP slowly per second but has an enormous capacity, regenerating ATP for hours as long as fuel and oxygen keep arriving.
3. Aerobic ATP production happens inside the mitochondria of the muscle fibre.
4. Type I muscle fibres are packed with mitochondria, which is why they specialise in endurance activity.

All three systems run together in most sports

1. The body never relies on a single energy system alone.
2. A 400 m race uses all three in sequence: the first 50 m draw on the ATP-PC system, the middle shifts to anaerobic glycolysis, and the final 100 m mixes glycolysis with aerobic contribution.
3. Even an endurance event has anaerobic moments, such as a final kick at the finish line or a surge to drop a competitor.

Malnutrition reduces muscle function and performance

1. Adequate nutrition is needed to maintain energy supply, muscle contraction, and recovery.
2. Malnutrition can result from nutrient deficiencies or inadequate caloric intake.
3. It can lead to muscle weakness, fatigue, and impaired performance.

Specific nutrients support muscle contraction and endurance

1. Protein is required for muscle growth, repair, and function, and amino acids from dietary protein build and repair contractile proteins inside the muscle fibre.
2. Carbohydrate is the primary fuel source for muscular contractions, stored as glycogen in the muscle and liver.
3. Fat is an important energy source during prolonged, lower-intensity exercise, especially when glycogen stores become limited, and it is the largest energy store in the body.
4. Electrolytes such as sodium, potassium, calcium, and magnesium are essential for nerve signalling and muscle contraction, and imbalance disrupts the membrane potentials that trigger contraction, producing muscle cramps.
5. Iron is essential for haemoglobin in red blood cells and myoglobin inside muscle, both of which carry oxygen to working tissue.
6. Water keeps blood volume up so oxygen and nutrients can reach the muscle.
7. B vitamins and calcium also play essential roles in energy metabolism and muscle activation.