Like pharmacological drugs, physical exercise may be chemically addictive. Addiction can be defined as the frequent engaging in the behavior to a greater extent or for a longer time period than intended. It is theorized that this addiction is due to natural endorphins and dopamine generated and regulated by the exercise. Whether strictly due to this chemical by-product or not, some people can be said to become addicted to or fixated on psychological/physical effects of physical exercise and fitness. This may lead to over exercise, resulting in the<unk> " syndrome.
Overtraining
Deconditioning
Preconditioning 
Allostatic load
Stress shielding
Homeostasis
Neuraxial blockade
Meditation