9 Fatigue

• Fatigue


  The inability to maintain power output during repeated muscle contractions
• Different types of fatigue

  • Central/mental fatigue
  • Peripheral fatigue
• High intensity and endurance activities

  • High intensity exercise involves a vigorous bout of intense exercise that may last for less than a second to as long as 1-2 mins (interval/plyometrics)
  • Endurance activities involve prolonged sessions of low intensity activity of several minutes to several hours (cycling/jogging)
• Causes of fatigue


  • Tiredness from overtraining
  • Lactic build up
  • Insufficient energy source
• Central/mental fatigue

  Develops during prolonged exercise and is caused by impaired function of the CNS. It is a type of fatigue associated with changes in the synaptic concentration of neurotransmitters within the CNS (including brain and spinal cord) which affects exercise performance and muscle function
• Peripheral fatigue


  Depletion of energy and inhibition of muscle contractions due to metabolites. Develops rapidly and is caused by reduced muscle cell force
• Fatigue may be viewed as a simple imbalance between ATP requirement of the muscle's ability to resynthesise ATP, depletion of PC reduced ATP resynthesis thus power output decreases
• Muscle fatigue


  The inability of the muscle to maintain a contractile force
• High intensity exercise


  • The major sources of energy (ATP production) for this is derived from anaerobic process
• Endurance activities


  • The major source for endurance activities are aerobic processes
• Exercise intensity


  The amount of physical power (expressed as a percentage of the maximal oxygen consumption) that the body uses when performing an activity
• Fatigue is perceived differently by individual athletes and may depend on multiple factors such as age, level of fitness and the specific type of activity or exercise carried out
• Onset of blood lactate accumulation (OBLA)


  The level of lactic acid in the blood reaches 4mmol, caused by the build up of lactic acid during anaerobic respiration in the muscles
• Phosphocreatine/ATP-PC energy system


  1. Phosphocreatine (PC) is broken down to produce a P molecule and enough energy to bind the P with ADP to produce ATP

  2. For every PC molecule one molecule of ATP can be produced

  3. Allows for quick production of ATP, used for short burst of maximal work with no waste products

  4. PC-stores can be replenished but can take up to 3/4 mins to fully recover

  
• Lactic acid system


  1. Glucose begins to breakdown, glycolysis, H+ is released as in aerobic breakdown and enter the electron transport chain

  2. But due to the lack of oxygen, the H+ doesn't combine with oxygen to form H2O but instead combines with pyruvate to form Lactic Acid

  3. Lactate system is not as rapid as the ATP-PC system as there are more chemical reactions involved in the process therefore it produces energy slower than the ATP-PC system
• Muscle fatigue


  • The inability of the muscle to maintain a contractile force
  • Caused by increased acidic level (build us of H+ and lactic acid), no glycogen left to continue, and the chemical reactions involved in energy production interfering with the nervous stimuli that allow contractions to occur
• Recovery


  1. Restore levels of ATP

  2. Reduce the level of lactic acid

  3. Restore levels of phosphocreatine

  4. Reload myoglobin

  5. Restore glycogen levels
• Excess post oxygen consumption (EPOC)

  • Elevated body temperature
  • Resynthesis of phosphocreatine in muscle
  • Lactate removal
  • Restoration of muscle and blood oxygen stores
  • Elevated hormones
  • Post-exercise elevation of HR and breathing
• Glycogen store after a heavy training session can be depleted – requiring the need for high carb meal to replenish the loss. It has been noted that consuming high carb meals within an hour of completing exercise will help improve glycogen recovery