INTRODUCTION:
Exercise is very relevant in many people’s day-to-day lives, as it as many beneficial health effects. Fatigue is a feeling experienced by most people, especially during exercise. Fatigue is understood to be one of the body’s defense mechanisms that maintains the physiological integrity of the body (16). Signals that come from the brain during exercise stop physical exertion or reduce its intensity, and act as a safety mechanism to prevent the limit of physiological changes during exercise to be exceeded (16). During prolonged exercise, the physical fatigue that sets in is a result of peripheral mechanisms such as depletion of muscle glycogen, decreased plasma glucose, and increased plasma free fatty acids (24). Peripheral fatigue …show more content…
Serotonin, dopamine, and norepinephrine are neurotransmitters that are directly related to fatigue, which ultimately leads to reduced intensity or stopping physical activity, therefore altering performance (19). The central fatigue hypothesis is a common theory that assumes that during prolonged exercise, the synthesis and metabolism of central monoamines, specifically serotonin, dopamine, and norepinephrine are activated (17). It was first determined that during exercise, increased serotonergic activity in the brain could cause tiredness and less motivation, which results in a quick cessation of exercise (3). More recent studies on the central fatigue hypothesis have found that the interaction between brain serotonin, dopamine, and norepinephrine during prolonged exercise could play a major role in the onset of fatigue. …show more content…
(23), it was found that a group of trained high performance rats had lower 5-HT levels at rest than low performance groups, which suggests that rats with higher exercise capacity have lower 5-HT activity, even at rest (23). It was also found that the high performance rats had higher measured 5-HT activity during exercise but they continued to exercise for longer than the low performance rats (23). This suggests that the highly trained rats could tolerate higher serotonergic activity while exercising and therefore can tolerate more feelings of fatigue before stopping exercise (23). A study done by Corderio et al. (3) agreed with this because they found that exercise training from 6 weeks of wheel running decreased the sensitivity of 5-HT receptors in rats and prolonged the release of dopamine (3). The six weeks of wheel running also increased the mRNA for tyrosine hydroxylase, which enhanced the activity of the dopaminergic system and promoted a down-regulation of the serotonergic system. (3) These studies prove that physical training can reduce the fatigue effects that serotonin may cause, as well as introduces the topic of the dopaminergic system down-regulating the serotonin system, lessening