PED Ch7 - Fatigue and recovery

Fatigue

The point at which the body’s ability to sustain a given level of intensity is reduced. This results in the working muscles producing slower and less forceful contractions, causing a decline in performance

Three types of fatigue

• Fuel depletion

• Accumulation of metabolic by-products

• Thermoregulation

Individual factors affecting fatigue

Age, genetics, fitness, pre-exercise nutrition and hydration, psychological arousal

Exercise conditions affecting the major fatigue mechanism

• Intensity and duration

• Type of exercise (intermittent or continuous)

• Type of contraction (dynamic or isometric)

• Environmental conditions

When does CP depletion occur?

After about 10 seconds of maximal exercise using the ATP-CP system or during repeat intermittent maximal efforts

Why does CP depletion cause fatigue?

CP depletion causes increased contribution from the anaerobic glycolysis system, which has a slower rate of ATP resynthesis, reducing the speed of muscular contractions

When does glycogen fuel depletion occur?

After about 90 minutes of submaximal exercise using the aerobic energy system

Why does glycogen fuel depletion cause fatigue?

When muscle glycogen stores are depleted, fat becomes the main fuel source. Fats have a slower rate of ATP resynthesis than glycogen because they are more complex molecules and require more oxygen to be broken down, causing a reduction in intensity

Hitting the wall

A term used in endurance sports that describes the sudden feeling of extreme fatigue when glycogen stores are depleted

When does H+ accumulation occur?

• When the anaerobic glycolysis system is the main contributor to ATP resynthesis

• When working above LIP using the aerobic energy system

Why does H+ accumulation cause fatigue?

Hydrogen ions reduce the rate and force of muscle contractions, decreasing power output

Lactate inflection point

The last point at which lactate production equals lactate removal

Typical LIP for an untrained individual

55-70% VO2 max

Typical LIP for a well-trained individual

75-90% VO2 max

When does thermoregulatory fatigue occur?

• During high-intensity endurance events

• While playing sports in summer months or hot, humid conditions

• Extended use of the aerobic energy system

Why does thermoregulation cause fatigue due to increased body temperature?

• Increased body temperature forces blood redistribution away from the muscles via vasoconstriction and towards the skin via vasodilation

• This reduces the delivery of oxygen to working muscles, slowing the rate of ATP resynthesis and exercise intensity

Why does thermoregulation cause fatigue due to dehydration?

• Increased sweating reduces blood plasma and blood volume

• Reduced blood plasma increases blood viscosity, slowing blood circulation and decreasing stroke volume, causing heart rate to increase

Simple carbohydrates/sugars

Digested and absorbed quickly, providing an immediate release of energy

E.g. watermelon, lollies, gels, sports drinks

Complex carbohydrates/starches

Digested and absorbed slowly, providing a gradual, sustained release of energy

E.g. pasta, wholegrain bread, yoghurt, grains

Pre-exercise carbohydrate consumption (carbohydrate loading)

Athletes should consume complex carbohydrates 2-3 hours before endurance exercise to delay glycogen depletion. Carbohydrate loading can be performed 2-3 days prior to endurance competition to maximise glycogen stores.

Carbohydrate consumption during exercise

Athletes should consume simple carbohydrates to quickly top up blood glucose levels for immediate energy during events lasting over 60 minutes

Post-exercise carbohydrate consumption

Athletes should consume carbohydrates in the first 30-60 minutes post-exercise when the body is most receptive to converting glucose to glycogen

Purpose of protein consumption after exercise

Amino acids are important for muscle growth and repair

Why should proteins and carbohydrates be consumed together after exercise?

Protein increases the absorption of carbohydrates, accelerating the replenishment of muscle glycogen stores

Recovery to protect the immune system

Consume carbohydrates, vitamin C and E, glutamine, zinc and probiotics

Dehydration

The result of thermoregulatory fatigue in the form of sweating that causes reduced blood volume, decreasing the delivery of oxygen to the working muscles

Pre-exercise water consumption

Athletes should drink water before exercise to lower the risk of becoming dehydrated during exercise

Water consumption during exercise

Water intake can enhance performance by maintaining a stable body temperature, enabling ATP production and reducing the impact of thermoregulatory fatigue

Post-exercise water consumption

Athletes should drink water after exercise to return the body to pre-exercise fluid levels

Role of sports drinks

Sports drinks contain carbohydrates which replenish glycogen stores and electrolytes which drive the thirst mechanism and increase fluid absorption

Benefits of milk consumption post-exercise

Milk contains water, carbohydrates, proteins, fats and sodium