Identify and Describe theDifferent Types of Fatigue and the Main Mechanisms of Fatigue. Ensure the Roleof Metabolites In Fatigue Is Also Discussed.

AS and A Level Physical Education (Sport & Coaching)

IDENTIFY AND DESCRIBE THE DIFFERENT TYPES OF FATIGUE AND THE MAIN MECHANISMS OF FATIGUE. ENSURE THE ROLE OF METABOLITES IN FATIGUE IS ALSO DISCUSSED.

FOR THE THREE SPORTS SELECTED IN PART 1, DISCUSS AND PROVIDE EXAMPLES OF HOW AN ATHLETE CAN IMPROVE THEIR RECOVERY FROM FATIGUE INDUCED BY PARTICIPATION IN EACH SPORT. COVER ALL ASPECTS OF RECOVERY, INCLUDING PHYSICAL, PHYSIOLOGICAL AND PSYCHOLOGICAL.

According to McArdle, Katch and Katch, Exercise Physiology , 4th edition, Fatigue is defined as “ the decline in muscle tension capacity with repeated stimulation”. Simply it means that as the athlete progresses in his/her activity, muscle tiredness accompanied by laboured breathing sets in and this would result in decreasing performance in the said activity as it progresses further.

Fatigue is the result of many factors, each of which is the direct result of the activity or exercise that produces it. As we know it , voluntary muscle action is the result of a chain of events involving the following areas in the following order:

The central nervous system involving proximal motor neurons (mainly in the brain)
The peripheral nervous system within the motor units ( ie motor neurons, peripheral nerves, motor end plates and muscle fibers)
The neuromuscular junction
The muscle fiber function

Now when this chain of events between the central nervous system and the muscle fiber junction is interrupted, fatigue would result.

Muscle Fatigue occurs when muscular performance is impaired ie when the muscles fail to maintain a certain workload . This fatigue is caused by a depletion of energy fuel such as glycogen or PC, accumulation of lactic acid and a dramatic increase of H+ concentration in the active muscles in trained and untrained individuals during prolonged high intensity exercise. Local muscular fatigue occurs in the fast twitch fibers ( type II) rather than in the slow twitch fibers ( type I ).

Nutrient Fatigue occurs when the active muscle fibers experience a major reduction in glycogen content during prolonged sub maximal exercise.

Neural fatigue occurs at the neuromuscular junction when an action potential fails to cross over from the motor neuron to the muscle fiber.

There are several factors that cause fatigue and they are:

Depletion of Phosphocreatine

As we know it that energy for muscular contraction is supplied by ATP and its continual resynthesis. When Phosphocreatine is rapidly depleted during the time the muscles are subjected to repeated maximal contractions, the body’s ability to replace the spent ATP is hindered. As a result of this, the muscles are deprived of sufficient ATP to sustain the muscle contractions and fatigue and the subsequent deterioration in performance results.

Production of Lactic Acid

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Production of Lactic Acid

Lactic Acid is the by product of anaerobic lactic glycolysis. In the process of glycolysis, glycogen is broken down to pyruvic acid. As glycolysis is carried out without oxygen , the pyruvic acid is changed to lactic acid which causes fatigue. The presence of lactic acid in the blood will decrease the pH value of the blood making it more acidic and thus will affect the muscle and neural function. Onset of Blood Lactate Accumulation ( OBLA ) will occur at about 55% VO2max for the untrained athlete and at 80% for the trained athlete. Therefore, it is seen that lactic acid accumulation will occur in the muscles during prolonged and high intensity exercise. The hydrogen ions will break away from the lactic acid leaving the lactate behind which causes the sensation of pain in the muscles and fatigue. This is experienced in short high intensity exercise nsuch as running the 400metres sprint. What happens is that the breakaway hydrogen ions will increase the acidity in the muscles causing a decrease in the pH value. The decreased pH will inhibit the action of the glycolytic enzymes thus preventing further release of energy from glycogen.

Neural Transmission Failure

During maximal muscle contraction, the neural transmission frequency is high and as a result of this maximum tension in the muscles occurs through the recruitment of many muscle fibers. When this happens, the fast twitch fibers find it difficult to maintain tension probably due to the impairment of neuromuscular transmission at the nerve endings in the muscle and fatigue occurs quickly in about 2 to 6 secs. The impairment could be due to an accumulation of extracellular potassium ions which would change the electrical potential across the muscle membrane and the nerve endings. The fatigue so caused in a localized muscle group, is short in duration . In a sprint event, the recovery may be longer but in a training environment, several sprint repetitions would be possible if there is provision for recovery periods inbetween repetitions.

Depletion of Calcium Ions

When slow twitch fibers are recruited for exercise, fatigue would still result but at a slower pace than in high intensity exercise. Fatigue in this case is thought to be caused by the impaired electrical activity and the chemical changes that induce muscle shortening .The ability to sustain muscular contractions is reduced and this is thought to be caused by the depletion of intracellular calcium ions that paly an important role in the contraction process. Post exercise diet and recovery activities would be needed for the athlete to recover from this type of fatigue.

Depletion of Glycogen

In prolonged exercise that lasts for several hours, fatigue develops as glycogen becomes depleted in the slow twitch fibers and the fast twitch fibers are recruited maximally. When this occurs, further recruitment of fast twitch muscle fibers is no longer possible to compensate the decline of activity in the slow twitch fibers and power output from the muscles begin to decline thus affecting performance. Recovery from this type of fatigue would take days depending on the type of activity and the severity of the damage to muscles that has occurred.

Reference: 1 Nadel E.R. ( 1985) Psychological Adaptations to Aerobic Training

Course Notes on Fatigue and Recovery provided by Blackburn College

Macardle, Katch and Katch , Exercise Physiology , 4th Edition
Part 2

The body of an athlete can recover from fatigue from participating in a sprint event or a tennis match or a marathon race through the following process:

Replacement of lost glycogen
Removal of lactic acid
Replacement of ATP
Replenishment of oxygen in myoglobin

For the replacement of glycogen, removal of lactic acid and replacement of ATP, a large amount of oxygen would be needed and this phenomenon id known as oxygen debt or post exercise oxygen consumption. To adequately remove lactic from the blood a copius amount of oxygen would be required.

Physiological Recovery

For the three selected sports ie tennis, sprint and the marathon, the replenishment of energy fuel and fluid is of utmost importance. CHO loading is especially important before, during and after competition. CHO loading will maximize glycogen stores and thus minimize the onset of fatigue. The recommended intake of CHO is 1 gram per kg body weight per hour during competition.

Replenishment of fluid loss to minimize the risk of dehydration is also very important for the recovery process. For events lasting less than 60 mins, water is sufficient to replace fluid loss. For tennis and marathons, isotonic sports drinks such as Gatorade or 100 plus will help to restore the electrolyte balance in the body and thus aid in the recovery process. Zinc and Magnesium are important for muscle repair and replacement. Potassium in conjunction with Sodium will help to maintain fluid and electrolyte balance in the cells and is important for nerve and muscle function. Potassium also helps to lower blood pressure and a deficiency in Potassium would result on high BP, dry skin , salt retention and irregular heartbeat. Deficiency in Sodium would result in low blood sugar, dehydration, lethargy, and heart palpitations leading to possible heart attacks. Therefore Potassium and Sodium are very essential minerals that need to be replaced quickly for recovery.

Physical Recovery

Stretching and cooling down are very important for the recovery of the athlete after a grueling tennis match, a competitive marathon or a sprint. Stretching will improve posture and flexibility and it will be good for the athlete to include stretching and cooling down to aid quick recovery.

Cross training such as swimming light jogging and hydrotheraphy such as saunas, massage and spas would stimulate the nerves and improve blood circulation to aid quick recovery.

Psychological Recovery

Athletes in the three events ie tennis , marathon and sprint could listen to stimulating and calming music to help them to relax before and after the event for optimal arousal and relaxation and recovery.

Proper breathing techniques while stretching will also help to relax tense muscles thus aiding the recovery of the athlete.

Meditation would help the athlete to relax as well as calm the nerves by reducing the noise to the brain. It would help the athlete to lower the BP, heart and breathing rate, relaxes the muscles and controls stress all of which are important for the athlete before and after the competition.

Finally , imagery and visualization would help the athlete to invoke the best performance and for relaxation.

Proposed Recovery For Tennis , Sprint( 100 metres) and Long Distance Running

( Marathon )

Reference : 1 Course Notes provided by Blackburn College