Persistent or severe stress (trauma) can have a severe impact on a person's physical health. While it is difficult to specify the exact biological processes which underlie a person's response to dramatic situations it has been found the bodies reaction to sustained and excessive stress (trauma) typically occurs in three major phases:

alarm reaction - in which the bodies defensive forces are "called to arms" by activation of the autonomic nervous system;

stage of resistance - in which biological adaptation is at the maximum level in terms of bodily resources used; and

exhaustion - in which bodily resources are depleted and the organism loses ability to resist so that further exposure to stress can lead to illness and death.

If the stress has resulted in extensive damage, this restorative process is often a matter of helping people reorganise the adaptive processes, defences, and routines that they had before the trauma caused their disorganisation. However, individuals may not be as effective in dealing with routine problems as they were before the trauma.

Stress and the sympathetic nervous system

The sympathetic nervous system plays an important part in response to stress or dangerous situations. When a person is faced with danger, the sympathetic nervous system discharges adrenaline to prepare the person for the "flight or fight" response. This consists of:

1. increasing the heart rate and blood flow to the large muscles to ensure the capability of reacting to any physical threats;
2. the pupils are dilated so that more light enters the eye;
3. the skin is constricted to limit blood loss in the event of injury;
4. blood sugar is increased to provide more ready energy.

Even though this biological reaction has been hard coded into all of us since caveman days we seldom find ourselves in the type of circumstances that require this flight or fight response. Once the flight or fight response has prepared us for physical combat what happens after the physical threat vanishes? It was thought that after a very stressful experience rest could completely restore us. However, experiments on animals have clearly shown that each exposure leaves an indelible scar, in that it uses up reserves of adaptability, which cannot be replaced. It is true that immediately after some commenting experience rest can restore us almost of the original level of fitness by eliminating acute fatigue. But the emphasis is on the word almost. Since we constantly go through periods of stress and rest during life, even an minute deficit of a adaptation energy every day adds up - it adds up to what we call ageing.