Effect of physical exercise on depressive state has been well demonstrated in adolescent females with mild depression. Twenty-four hour excretions of cortisol and epinephrine in urine were reduced by exercise regimen (Nabkasorn et al., 2006). Exercise also stimulates the secretion of endogenous opioids and produces a state of euphoria (Janal et al., 1984; Sher, 1998; Boecker et al. 2008).
Exercise also promotes the secretion of neurotransmitters like serotonin and dopamine (Ransford, 1982). The exercising rats showed less anxious behavior in the novelty situation. The changes in the sympatho-adrenomedullary input may play an important role in these distinct cortisol responses to stress (Droste et al. 2007).
Receptors on nerve fibers are excited in response to rhythmic discharges of strong muscle contractions induced by physical exercise. This somato-sensory stimulation induced by exercise is carried to the brain stem and central nervous system, resulting in the release of endogenous oxytocin (OXT) (Andersson et al., 1995). OXT has been shown to have anti-stress effects via inhibiting HPA-axis (Windle et al. 1997).