Social aggression and isolation lead to increased levels of cortisol (stress hormone) and leads to potential mental health problems.
Cortisol is released in response to fear and stress by the adrenal glands as part of the fight/flight mechanism; the general adaptation syndrome.
Eustress and distress release cortisol as part of the general adaptation syndrome. It builds up in the blood and wreaks havoc on the body. Eustress creates the "seize the day," heightened state of arousal, it is invigorating and linked to a tangible goal, whereas distress is free floating anxiety with no outlet for the cortisol; it causes the fight/flight to backfire.
Regular physical activity can recreate the "fight" response to let out aggression and reduce cortisol. Fear increases cortisol and regular activity decreases fear by increasing self confidence, resilience, and fortitude to decrease the cortisol; (psychologytoday.com)