The word fatigue means feeling of tiredness. It can be the result of infection, recovery from injury or surgery, mental depression or sleep deprivation etc. However, today I am going to talk about the physiological fatigue during physical exercise.
To start with the chain of process of muscular contraction that brain is the commander to direct the motor unit reflex throughout spinal cord then to motor neuron cell body to create neural signal reach to muscle for the metabolism which called cross bridge reaction
It is obvious that impairment anywhere along the chain of command from Brain to Muscle contractile protein will affect the force and power output. Then fatigue become the final result. There are 4 underlying physiological cause of fatigue can be classified as followings
1. The shortage of energy systems that impact on energy delivery during a anaerobic condition for example when the intensive session ended, during the recovery duration, Phosphoc Creatine resynthesis will be carried out, but one may have less Pc storage in muscle
2. Glycogen Depletion and lead to fatigue, because as PCr is using, the rate of muscle glycogen depletion is controlled by the intensity and duration of the activity. In events lasting longer than a 20 seconds, muscle glycogen becomes the primary energy source for ATP synthesis ( after PCr ) , less Glycogen is really cause fatigue in long term duration in exercise
3. Accumulation of Metabolic by product and fatigue are related with lactic acid. It accumulates within the muscle fiber only during high intensive muscle effort. the Accumulation of lactic acid result in excessive hydrogen ions which in turn cause muscle acidification, a condition known as acidosis (feeling sore and weakness in muscle)
4. Central nervous system switch off lead to fatigue, in most spots or HITT activities, the recruitment of muscle depends on conscious control, currently the detailed mechanism are not clear yet, some studies point out that poor Vo2 Max or weak blood stroke volume could delayed blood back to brain which could slow down the brain reaction
Exercise fatigue may happened in multiple processes rather than single process. It seem be a trouble maker to against exercise enjoyment, but we should be able to manage it and prevent fatigue as much as we can. Here I like to invite you have your comment to discuss the prevention
Thanks
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