Abstract
Pain is a complex phenomenon that has a motor component in addition to sensory, affective, cognitive and autonomic components. Once something hurts, movement is restricted, but on the other hand, physical activity weakens the perception of pain.
Although multiple systems are involved in the exercise-induced analgesia, the central role consists in the activation of the endogenous opioid system. During exercise, beta-endorphin is released, both central and peripheral, which subsequently increases the threshold and tolerance to pain.
Experiments on animals show that non-opioid systems, especially endocannabinoid, serotonergic and noradrenergic, are involved in the development of analgesia. Which system will be more activated depends, among other, on the intensity, type and duration of the exercise and, in the case of the swimming protocol, also on the water temperature.
Animal research has shown that voluntary exercise affects the plasticity of the brain. The positive effect in rats is manifested by increased levels of growth factors, stimulation of neurogenesis, increased resistance to cerebral ischemia, improved learning and mental performance.
In human, regular exercises have positive effects on the mental state, reduce anxiety and depression. Due to these mechanisms, it is understandable why the exercise has euphoric effects and why it can also be addictive.