topic 9 fatigue

Fatigue

A reversible reduction in performance due to exercise

Peripheral fatigue

Develops rapidly and is caused by reduced muscle cell force; usually associated with high intensity activity; also known as local fatigue as it occurs in the muscles being worked

Central (or mental) fatigue

Develops during prolonged exercise and is caused by impaired function of the central nervous system (CNS); linked to endurance activities; decreased ability to transmit and coordinate neural impulses leading to impact on muscles ability to complete required contractions and impaired decision making with increased reaction time

High intensity activities

Exercise involves a vigorous bout of activity that may last anywhere from as little as one second up to 1 or 2 minutes; some types include short and intermediate interval training or plyometrics; energy required is primarily derived from the two anaerobic energy systems

Endurance activities

Activities involve a prolonged session of relatively low-intensity that can last anywhere from several minutes to many hours; examples include cycling or jogging; energy for this type of exercise is made available through aerobic processes

Causes of fatigue

Fatigue is perceived differently by each athlete and is multifactorial, influenced by age, level of fitness, and type of exercise undertaken

Peripheral fatigue in high intensity exercise

Caused by depletion of energy stores (cp and atp); leads to using a slower rate of energy production through slower energy systems; cp depletes in 15 secs, dominant energy system for 10; ATP depletes in 2 secs; glucose not included as not depleted until 90 mins; increase in levels of the by-products of exercise such as lactate and hydrogen ions

Hydrogen ions

Increase acidity/decrease pH and inhibit glycolytic enzymes which decrease the rate of the anaerobic glycolysis system; increased acidity means glycogen can't be broken down as fast

Peripheral fatigue in endurance activities

Depletion of muscle and liver glycogen stores (90+ mins); reduction in Ca++ release leading to slower attachment of myosin X-bridges to actin; depletion of acetylcholine which helps convert nervous system signals into chemical signals in muscle; electrolyte loss can cause cramp and is essential for chemical reactions involved in the sodium potassium pump; dehydration leads to increased blood viscosity hence less O2 to working muscles; overheating leads to fluid loss to maintain homeostasis

Electrolyte loss

Can cause cramp; electrolytes help with chemical reactions involved in the sodium potassium pump and carry electrical charges needed for muscle contraction

Dehydration

Leads to increased blood viscosity hence less O2 to working muscles, increased HR to maintain intensity/Q, which accelerates fatigue

Overheating

Leads to fluid loss to lose heat to maintain homeostasis, causing cardiovascular drift and possibly dehydration; a byproduct of aerobic energy, inefficient heat release results in vasodilation and sweat

Central (mental) fatigue

A significant factor in many endurance sports caused by failure of neural transmission.

Central nervous system inhibition

When brain detects local fatigue it sends out inhibitory signals to stop further muscular contraction, resulting in fewer electrical signals and less forceful and less frequent muscle contractions.

Neurotransmitter depletion

Ach is required to convert electrical signal of nervous system to chemical signal in muscles. As intensity increases, get to point where Ach release is reduced, leading to less muscle stimulation and fewer and less forceful muscle contractions.

EPOC

Excess post-exercise oxygen consumption, which repays the oxygen deficit that occurs at the start of exercise due to the delay in HR increase.

EPOC fast component

Alactacid oxygen debt, which involves restoration of creatine phosphate stores and replenishment of myoglobin.

EPOC slow component

Lactacid oxygen debt, which involves the removal of accumulated lactic acid.

Other EPOC functions

Return cardiac and pulmonary functions to resting levels, including heart rate and respiratory rate, and return core temperature to normal.

Glycogen

The stored form of glucose, found in muscles and the liver, serving as a key energy source during exercise.

Glycogen resynthesis

The process by which the body works to restore glycogen levels post-exercise, using carbohydrates from the diet.

Consequences of Inadequate Glycogen Replacement

Fatigue and performance decline in subsequent workouts or events due to insufficient energy, and decreased ability to maintain high-intensity efforts and endurance during prolonged activities.

Recovery Strategies

Methods to enhance glycogen storage, including carbohydrate loading, timing of carbohydrate intake, and a balanced diet.

Carbohydrate loading

Consuming carbohydrate-rich foods post-exercise to maximize glycogen storage.

Timing of carbohydrate intake

Consuming carbs immediately after exercise and within 30 minutes to 2 hours can enhance glycogen resynthesis.

High GI foods

Foods with a high glycemic index that can be consumed to aid in glycogen replenishment.

Window of opportunity

The 30 minutes to 2 hours post-exercise period during which carbohydrate consumption is most effective for glycogen replenishment.

Muscle and liver glycogen replenishment

Both muscle and liver glycogen can be replenished within 24 hours of activity.

Carbohydrate intake post-exercise

Consume 1.2g of carbohydrates per kg of body weight immediately after exercise and at regular intervals.

Muscle glycogen preference

Muscle glycogen will replenish preferentially over liver glycogen.

Total carbohydrate intake for replenishment

5-12g of carbohydrates per kg of body weight in total should replenish glycogen in 24 hours.