Fatigue (physiology)

Fatigue is a mostly temporary ( reversible ) reduction in physical and / or mental performance . A distinction is made between mental fatigue of the central nervous system (CNS) and peripheral , physical fatigue of the muscles .

Physical fatigue

Peripheral or physical (physical) fatigue is the reduced strength of one or more muscles compared to the strength that is otherwise to be expected depending on the individual physical performance . It occurs mainly with local exposure and poor training condition . The reduced performance is reversible and can be partially compensated by increased use. If up to a seventh of the muscle mass is fatigued, the fatigue is considered local , and beyond that, general . It is generally known that local fatigue is discipline-specific. In cross-country skiing, lactate is distributed between the stressed and the less stressed muscles during the race. As a result, with the double arm swing, when the arms produce more lactate than the legs and than they can process themselves, the lactate is distributed to the large leg muscles when downhill and is broken down and converted there. The local muscular endurance of cross-country skiers (full body load), orienteers (lower body load) and canoeists (upper body load) of international class showed that not only the muscle mass used in the sport itself, but also the amount of training played a role in the adaptation of the local muscular blood flow.

Mental fatigue

Central (CNS) or psychological (mental) fatigue can occur independently of muscular fatigue and mostly manifests itself through subjective sensations and a visible deterioration in movement coordination . It occurs mainly with complicated and complex loads. The reduction in performance is the result of a disturbed central nervous system. The reticular formation , an area of the brain that inhibits the other motor systems of the central nervous system , occupies a central position . The inhibitory processes have the effect, among other things, of impairing the absorption of information (sensory perception) and slower information transmission and processing. From a psychological point of view, the tolerance of stress is a coping process .

Symptoms

From a sports medicine point of view, subjective and objective symptoms of fatigue can be determined, which are used to assess or assess the degree of fatigue. The correlation between the subjective statements of fatigue and the objectively verifiable factors is low and depends heavily on the level of training and the sporting experience of the person concerned. An untrained person will psychologically tolerate less stress than, for example, a competitive athlete.

Subjective

Lenses

Declining muscle strength
Extended refractory period
Rising stimulus threshold
Decreased reflex responses
Muscle tremors (tremor)
Incoordination
Electrolyte shifts , increase in lactate , pH changes so Glykogenverarmung , hormone levels decrease
Changes in brain wave activity (EEG)
Reduced concentration and attention , deterioration in perception

causes

Possible causes of fatigue, especially with regard to endurance training, are:

Depletion of energy reserves ( creatine phosphate , glycogen )
Accumulation of intermediate and end metabolic substances ( lactate , urea )
Inhibition of enzymes due to acidification or changes in the concentration of the enzymes
Electrolyte shift ( potassium and calcium on the cell membrane )
Depletion of hormones with constant heavy use ( adrenaline and noradrenaline as neurotransmitters , dopamine in the central nervous system)
Changes in cell organelles ( mitochondria and on the cell nucleus )
Inhibitory processes in the central nervous system due to monotonous loads (excessive demands due to insufficient demands)
Changes in regulation in the cellular area at the level of individual organ systems with regard to the integrating control center

Fatigue as a protective mechanism

As a normal regeneration phenomenon , fatigue is the physiological protective mechanism for maintaining homeostasis and is referred to as acute fatigue .

Fatigue resistance

Fatigue processes can be more or less compensated for over a certain period of time. The so-called fatigue resistance is influenced by the following factors, of which the level of training and motivation are particularly important:

Starting position (training status, age , health status , gender )
the previous load ( duration, intensity, type of training )
Attitude of the athlete to the load (motivation, interest )
mental resilience

Individual evidence

↑ ^a ^b ^c ^d Andreas Hohmann; Martin Lames; Manfred Letzelter: Introduction to Training Science . Limpert, Wiebelsheim 2007, ISBN 978-3-7853-1725-9 , pp. 50-51 .
↑ ^a ^b ^c ^d ^e ^f Fritz Zintl: Endurance training . blv, Munich 2009, ISBN 978-3-8354-0555-4 , p. 31-32 .
^ Van Hall, G., Jensen-Urstad, M., Rosdahl, H. et al. (2003), Leg and arm lactate and substrate kinetics during exercise, Am. J. Physiol. Endocrinol. Metab. , 284 (1), 193-205
^ Arnd Krüger : Ski sprint. Competitive Sport 46 (2016) 2, pp. 15-17.
↑ Lundgren, KM, Karlsen, T., Sandbakk, O. et al. (2015), Sportspecific physiological adaptations in highly trained endurance athletes, Med. Sci. Sports Exerc. , 47 (10), 2150-2157.
^ Diether Gotthold Roland Findeisen , P. Linke, L. Pickenhain: Basics of sports medicine. Barth, 1980, quoted from Andreas Hohmann, Martin Lames, Manfred Letzelter: Introduction to training science . Limpert, Wiebelsheim 2007, ISBN 978-3-7853-1725-9 , pp. 50 .

[Hohmann50-1] Andreas Hohmann; Martin Lames; Manfred Letzelter: Introduction to Training Science . Limpert, Wiebelsheim 2007, ISBN 978-3-7853-1725-9 , pp. 50-51 .

[Zintl-2] ↑ ^a ^b ^c ^d ^e ^f Fritz Zintl: Endurance training . blv, Munich 2009, ISBN 978-3-8354-0555-4 , p. 31-32 .

[3] Van Hall, G., Jensen-Urstad, M., Rosdahl, H. et al. (2003), Leg and arm lactate and substrate kinetics during exercise, Am. J. Physiol. Endocrinol. Metab. , 284 (1), 193-205

[4] Arnd Krüger : Ski sprint. Competitive Sport 46 (2016) 2, pp. 15-17.

[5] Lundgren, KM, Karlsen, T., Sandbakk, O. et al. (2015), Sportspecific physiological adaptations in highly trained endurance athletes, Med. Sci. Sports Exerc. , 47 (10), 2150-2157.

[6] Diether Gotthold Roland Findeisen , P. Linke, L. Pickenhain: Basics of sports medicine. Barth, 1980, quoted from Andreas Hohmann, Martin Lames, Manfred Letzelter: Introduction to training science . Limpert, Wiebelsheim 2007, ISBN 978-3-7853-1725-9 , pp. 50 .