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Physiological aspects of CFS

Many people with CFS are concerned that their distressing symptoms may be related to a disease that hasn't been detected. Others are concerned that a virus (if one occurred at onset) is still present or has caused physical damage to the body. However, intensive research has tried to establish whether disease, deficiencies or any other abnormal changes in the body may explain the very distressing and debilitating symptoms experienced by people with CFS.

To date, it appears that there is no one cause of CFS. Patients complain of a variety of different triggers, e.g. different types of infection or stressful life events. Some sufferers can pinpoint the exact date that it started. For others the onset is more gradual.

Difficulty maintaining previous activity levels is common to all sufferers. Some sufferers feel so ill that they rest for long periods and give up many of their previous activities including work, social activities and managing the home. Others may be able to function at a reasonable level, e.g. go to work or look after their family, but due to pushing themselves so hard in the day, may do very little in the evenings or at weekends due to their exhaustion. Others tend to do too much on "good days" and push themselves too hard for the level of their stamina resulting in resting for long periods on other days.

Over time, reduced or irregular activity and increased periods of rest cause physical changes in the body. These changes cause unpleasant sensations and symptoms that can be very distressing. It is important to point out that these changes are reversible with physical rehabilitation and/or exercise.
Research has looked at the effects of rest in healthy people when they reduce their activities and many similarities between CFS patients and healthy inactive people have been noted:

Changes in Muscle Function
Changes in the Cardio-Vascular System
Regulation of body temperature
Reduced calcium levels
Reduced tolerance to activity or exercise
Changes in the nervous system
Changes in mental functioning
Alteration of the biological clocks
Disturbance of the sleep-wake rhythm in CFS
Disturbance of cortisol production
Anxiety and Stress
Life Stress and Low Mood

Changes in Muscle Function

  • A decrease in the number of active cell mitochondria (tiny parts of the cell that act as a powerhouse) and their enzymes have been found in the muscles of CFS patients when compared with healthy active people. The reduction of cell mitochondria has also been found in healthy inactive people. Fewer cell mitochondria may lead to production of lactic acid at low exercise levels, which in turn limits muscle performance. These changes may account for the feeling of a lack of power or energy in the muscles.
  • As reduced activity leads to less efficient muscles (reduced strength, tone and size), it is more difficult for the muscles to squeeze the blood back to the heart causing blood to pool in the lower part of the legs. Pooling of blood can cause pain both during activity and rest.
  • When muscles are not used regularly, they become unfit or de-conditioned. When these muscles contract during activity, uneven stresses are produced. This may result in a feeling of weakness and instability followed by delayed pain and discomfort.
  • In all individuals, muscle pain and stiffness is a natural consequence of beginning a new exercise programme or when unaccustomed exercise is taken.

Changes in the Cardio-Vascular System

  • The cardiovascular system (which incorporates the heart and blood vessels) becomes out of condition very quickly with rest. The longer you rest the more changes occur.
  • Physical changes that occur with cardiovascular deconditioning include: (1) reduced blood volume after 1or 2 days bed-rest, (2) reduced volume of red blood cells after 8 days bed-rest which reduces oxygen carrying capacity of the blood, (3) volume of the heart reduces by about 15% after 20 days of bed-rest therefore less blood is pumped to other organs. These physical changes may result in making you feel breathless or dizzy when exercising, and contribute to your fatigue.
  • Following a "lying down" rest there is a drop in blood pressure on standing up (postural hypotension) due to blood pooling in the limbs and gravity when we stand up. Consequently, less blood returns to the heart and therefore less blood goes to the brain. The reduced blood flow to the brain causes dizziness and sometimes fainting on standing up.

Regulation of body temperature

  • Due to changes in the blood flow to major body organs following prolonged rest, changes in body temperature occur. This may result in feeling hot and or cold, with excessive and inappropriate sweating at times
  • Prolonged bed-rest results in a "headward" shift of bodily fluids. This may result in visual problems and sensitivity to noise.

Reduced calcium levels

  • During prolonged bed-rest, bones do not have to support the weight of the body or the pull of the muscles and lose calcium. Over a long period of time, this leaves bones brittle and easier to break

Reduced tolerance to activity or exercise

  • General de-conditioning of the body occurs as a result of prolonged rest or reduced activity. This results in being able to tolerate less activity as fitness reduces. Muscle fatigue, feeling of heaviness as well as a general increase in overall fatigue occurs when active.

Changes in the nervous system

  • One of the functions of the nervous system is to co-ordinate our muscles. However, regular performance of an activity is required to maintain good co-ordination.
  • Prolonged periods of inactivity therefore reduce our co-ordination.
This may result in unsteadiness, clumsiness and reduced accuracy on carrying out precise movements

Changes in mental functioning

  • Prolonged rest deprives people of intellectual stimulation and has a dulling effect on intellectual activity.
This may impair concentration, memory, and our ability to find the correct word

Alteration of the biological clocks

The central "clock", which is located in the hypothalamus of the brain regulates many body rhythms that run on an approximate 24 hour cycle. These rhythms are called circadian rhythms and they control vital functions such as:
  • sleeping and waking
  • feelings of tiredness and alertness
  • intellectual performance
  • memory
  • appetite
  • body temperature
  • the production of hormones, for example, cortisol
  • the activity of the immune system
Cicardian rhythms are responsible for your body "feeling" things at certain times of the day, for example, hunger, alertness, tiredness, needing to go to the toilet. The biological clock is affected by the events of the day and is reset each day by cues such as getting up or going to bed times, meal times and performing daily routines.

Recent research has also shown that there are "local" circadian rhythms within the body, with different systems and organs being more active at different times. There is also a third cycle, largely determined by night/day light/dark. it is now thought that part of the problems generated by disturbed diurnal routines are caused by not only these individual cycles being disturbed, but by them going out of synch. with each other. Your brain might think its 3am; your digestive system thinks its 8am (when it tends to be more active) but the light is telling you its noon. This dysynchronisation has been linked to many of the more common symptoms of CFS - disturbed sleep, poor digestion, alterations in appetite, headaches and of course fatigue.

The biological clock's time keeping can be disturbed if not reset by these cues in situations such as:
  • flying across different time zones (jet lag)
  • working shifts
  • during illness
If regular cues are lost, disruption of the clocks results in a slipping of body rhythms that can lead to: (1) the "normal" intense feelings of tiredness at night shifting into the day making it difficult to cope with your usual routine. (2) The "normal" daytime rhythm getting shifted around to the night, making you feel more alert and causing difficulty in getting to sleep.

This can lead to:
  • poor quality sleep at night
  • increasing fatigue during the day
  • poor concentration and forgetfulness
  • low mood
  • feeling unwell
  • headaches
  • muscle aches
  • loss of appetite
  • irregularities of bowel movement
  • alterations to immune functioning
As the symptoms of CFS are so similar to those of jet lag, circadian rhythms of people with CFS have been investigated. Evidence from some studies indicates that CFS is associated with the biological clock losing control of the body rhythms.

It is thought that an infection, a very stressful life event or an accumulation of persistent stress may contribute to us breaking our usual daily routine and normal sleep-waking cycle needed to reset the biological clock. This is because a stressful life event or an accumulation of stress can cause worry and disturb our sleep at night, leading to irregular getting up and going to bed times and increased rests during the day. The biological clock then loses control over body rhythms resulting in the above mentioned severe physical and mental symptoms of CFS.

Disturbance of the sleep-wake rhythm in CFS

Most CFS patients complain of poor quality sleep. Common problems include difficulty in getting to sleep, restlessness, wakening in the night and waking feeling unrefreshed and sleepy.

In a study where the sleep patterns of healthy volunteers was deliberately disrupted to be similar to those with CFS, they developed symptoms similar to those of CFS including feeling unrefreshed and physically weak, sleepiness, poor concentration and muscle aches. However, when they were allowed to sleep undisturbed, their symptoms subsided. This study indicates that a disturbed sleep pattern can cause some symptoms of CFS but that these symptoms are reversible.

Disruption of sleep can affect the activity of the immune system, possibly increasing vulnerability to colds and infection. Inactivity and being deprived of sleep cause an increase in the feelings of effort and fatigue when performing activity or exercise.

Disturbance of cortisol production

Cortisol is a hormone whose production is controlled by a circadian rhythm. Cortisol switches on our metabolism in the morning to prepare us for the physical and mental challenges of the day. Exercise and other stress causes an increase in the level of cortisol in the bloodstream. Prolonged stress however has been associated with lower cortisol in a kind of burn-out of the body's physiological coping mechanisms.

Research shows that some CFS patients have a lower level of cortisol, but no disease has been found that would account for this finding. Low cortisol is also shown in people who have been through trauma. The low cortisol levels found in CFS patients may also be associated with disrupted sleep and irregular activity.

Low cortisol levels have also been found in other people who have disrupted sleep such as a) healthy individuals who have rested in bed for more than 3 weeks b) healthy workers after working 5 nights of shift work c) people suffering from jet lag.

Low cortisol may add to the feeling of tiredness, decreased alertness and poor performance seen in CFS and night shift work. Whereas high cortisol allows us, in a flight or fight situation, to focus on the immediate threat, low cortisol is associated with difficulty in distinguishing the "important signal" from the "background noise" - like when you are in a crowded room and the background noise prevents you focussing on the person you are talking to.

This does seem to be a common experience of CFS. It would also account for some of the light and noise sensitivity. It is as if a crucial "filter" has been removed from the person's perceptual system. Re-establishing more "normal" activity and rest patterns, and dealing with stress should help to reverse these changes.

Anxiety and Stress

We normally think of anxiety as being all in the head. In fact it is largely a bodily thing and affects and involves most systems of the body. Anxiety is not always obvious either. It may be more like a background stress, subtle but persistent. The following is a description of some of the physiological components of anxiety. Bear in mind that they are not always as dramatic and obvious as a panic attack. The research shows that it is the persistent low grade anxiety - Stress in other words - that has the profoundest long term effects.

Anxiety is an automatic physical response of the body to a threatening or stressful situation. We can all remember having butterflies before an exam, an interview or going to the dentist! When we are in a situation that makes us feel anxious, there is increased activity of the central nervous system and an increased amount of the hormone adrenaline is released into the bloodstream.

These natural changes have a protective function in preparing us for action when we feel threatened or encounter a stressful situation. However, the physical feelings that we experience when anxious can be very unpleasant. Having CFS can at times be very stressful. Not only may you be dealing with feeling ill, but you may also have other concerns related to your illness such as concerns about finances if you are unable to work or worries about the cause and effects of CFS on yours and others lives.

These worries may at times trigger feelings of anxiety. Entering into a situation that you perceive as being stressful, whether doing something for the first time in months, increasing exercise etc, may lead to a further increase in anxiety. The physical effects of anxiety include the following:

  • Increased heart rate
This can be felt as a racing pulse, palpitations, pounding or tightness in the chest. Some people feel very frightened by these sensations and can become more anxious resulting in a further release of adrenaline that maintains the physical sensations. This also causes a rise in blood pressure.

  • Breathlessness which can lead to hyperventilation
This natural response to being anxious enables our lungs to be filled with oxygen to prepare us for action. However, if over-breathing (hyperventilation) continues for a while, an array of unpleasant symptoms may occur because it reduces the amount of carbon dioxide in the blood. This changes the balance of chemicals in the blood causing tightening of the blood vessels and reduced blood supply, especially in the brain.

This reduced blood supply to the brain causes sensations such as light-headedness, dizziness, faintness, feeling unsteady, clumsiness, blurred vision, pins and needles, tingling or numbness (sometimes one-sided) in the limbs or face. Cramp-like muscle spasms may be experienced, particularly in the hands and feet. Increased sensitivity to light and noise may also occur.

Other abnormal sensations such as feelings of being detached from oneself, feelings of unreality or being out of control may also occur. Feeling faint is misleading because overall blood pressure is high in anxiety and fainting only occurs when blood pressure is very low The muscles of the chest wall can be over-used during hyperventilation which may lead to chest pain or discomfort.

If these sensations are interpreted as a major problem, i.e. as a problem with the heart, it can lead to a further increase in anxiety and adrenaline production leading to an increase of unpleasant sensations. Over-breathing also results in increased use of the muscles of the head, neck and shoulders resulting in headaches, and localised stiffness and pain.

Over-use of the neck muscles in hyperventilation can be accompanied by sensations of tightness or a sore throat. Excessive mouth breathing and reduced saliva production may also occur as a result of the increased nerve activity and release of adrenaline. This causes a dry mouth, swallowing difficulties and the feeling of a lump in the throat.

  • Blood flow is altered
When anxious, blood is redirected to muscles to prepare for action. Reduced blood flow to the skin may cause pallor, pain, coldness of hands and feet and sometimes numbness or tingling. Reduced blood flow to the bowel affects the passage of food and can result in symptoms of irritable bowel, for example, constipation and or diarrhoea and abdominal discomfort.

  • Muscle tension: There is an increase in the tension of the muscles to prepare them for action. This can cause aches, pain (particularly in the shoulders, neck, jaws and head) and fatigue. Twitching or trembling muscles may also occur.
  • Visual disturbance: Increased nerve activity affects the muscles of the iris (coloured part of eye) causing dilation of the pupils, which lets in more light. The shape of the eye lens is altered to help improve side and distance vision. Together, these changes increase visual sensations that can be experienced as blurring of vision.
  • Sweating: Increased sweating occurs to allow for heat loss causing clammy hands and feet.
  • Sleep disturbance: As adrenaline arouses, sleep disturbance such as difficulty getting to sleep or frequent wakening is very common at times of stress and can be accompanied by nightmares and sweating.
  • Mental functioning: Anxiety may affect mental functioning in a number of ways and contribute to the following: Mood disturbance; e.g. irritability, being easily upset, Inability to concentrate, forgetfulness, indecisiveness, restlessness; e.g. fidgety, can't sit still, tendency to go over things again and again.

    Everyone experiences physical symptoms of anxiety in a different way and rarely experience all of the symptoms listed above. When these symptoms are extreme, they can easily be misinterpreted as signs of a serious disease that can trigger further unpleasant symptoms that can occasionally trigger a panic attack. An increase in nerve activity and adrenaline production can precipitate feelings of weakness and exhaustion that adds to the fatigue and muscle aches of chronic fatigue syndrome.

    During periods of prolonged physical or mental exertion, there is increased activity of the nervous systems and increased adrenaline production that leads to symptoms similar to those experienced in a flu like illness, such as aches and pains, headache, sweating, feeling hot and cold, chest tightness and sore throat. These symptoms may lead a person to reduce or avoid activities as they may believe that they are coming down with flu or a cold. As physical activity releases muscle tension, limiting activity can perpetuate the physical effects of anxiety and lead to further deconditioning.

Life Stress and Low Mood

Many patients experience major ongoing life stresses and problems related to the effects of their condition. These may include one or more of the following:
  • Financial difficulties due to no longer working, reducing hours etc
  • Worries about keeping a job or maintaining studies
  • Changing role within the family, i.e. loss of responsibility
  • Reduced social contacts leading to feeling isolated
  • Strained relationship with partner due to them having to do more at home
  • Feeling guilty about not being a "good" parent
These difficulties can understandably trigger feelings such as frustration, helplessness and loss of control over life. These feelings which are a natural human response to stress, can lead to low mood for some people and depression in others. Low mood can lead to a variety of problems including tiredness, which can further reduce the desire to be active. Further reduction in activity exacerbates the deconditioning process. Worrying about problems can disturb sleep at night, which can then lead to sleeping later the following day and contribute to developing a poor sleep pattern.


As we said there is good evidence to show that all of the above effects are reversible by a programme of gradual physical rehabilitation. Learning to spot and deal with sources of stress is also important. Lastly, not worrying too much about symptoms is probably crucial The more one worries about a symptom, the more one focuses on it, and the more stress this generates, which in turn worsens the symptoms.


Mary Burgess PhD
- based on the work of Pauline Powell.
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