Physiology of fatigue

PHYSIOLOGY OF FATIGUE
Dr Nishank Verma
MPT-Sports, PhD
Jamia Millia Islamia

FATIGUE FACTS
 Fatigue (either physical, mental or both) is a symptom that may be difficult for the patient to describe and words like
lethargic, exhausted and tired may be used.
 Taking a careful and complete history is the key to help making the underlying diagnosis of the cause for the symptom of
fatigue. However, in about a third of patients the cause is not found and the diagnosis is not known.
 There are numerous causes of fatigue symptoms. Examples of some treatable causes of fatigue include anemia, diabetes,
thyroid disease, heart disease and sleep disorders.
 Long lasting complaints of fatigue do not equate to chronic fatigue syndrome.

WHAT IS FATIGUE ?
 Fatigue is the felling of extreme tiredness or exhaustion, often involving muscle weakness.
 Fatigue is a message to the body to rest fatigue can compound until it becomes disturbing and eventually overwhelming.
Fatigue results in:-
 Slower reactions
 Reduced ability to process information
 Memory lapses
 Absent-mindedness
 Decreased awareness
 Lack of attention
 Underestimation of risk
 Reduced coordination
Slower
reactions
Reduced ability to
process
information
Memory lapses
Absent-
mindedness
Decreased
awareness
Lack of
attention
Underestimation of
risk
Reduced
coordination

WHAT IS THE CAUSE OF FATIGUE
 Lifestyle factors.
 Stress
 Dehydration
 Weigh Loss
 Too much activity
 Lack of exercise
 Cardiac issue
 Vitamin deficiencies
 Illness

SYMPTOMS OF FATIGUE
 There are many symptoms of fatigue. While it is common to experience the symptoms of fatigue occasionally, you
should see a doctor if you are feeling fatigued for two or more weeks.
 If the fatigue becomes constant, you may be suffering from Chronic Fatigue. The chronic fatigue symptoms are similar
to those of simple fatigue, however, the chronic fatigue symptoms are much more severe.
 Weakness
 Muscle aches
 Headaches
 Extreme sleepiness
 Lack of motivation
 Irritability

DIFFERENTIAL DIAGNOSES
 Certain medical conditions can cause chronic fatigue and must be ruled out before a diagnosis of CFS can be given. Hypothyroidism, A
nemia, Diabetes and certain Psychiatric disorders are a few of the diseases that must be ruled out if the patient presents with appropriate
symptoms.
 People with fibromyalgia (FM, or fibromyalgia syndrome, FMS), like those with CFS, have muscle pain, severe fatigue and sleep
disturbances. The presence of allodynia (abnormal pain responses to mild stimulation) and of extensive tender points in specific locations
differentiates FM from CFS, though the two diseases often co-occur.
 Fatigue and muscle pain occurs frequently in the initial phase of various hereditary muscle disorders and in several autoimmune,
endocrine and metabolic syndromes; and are frequently labelled as CFS or fibromyalgia in the absence of obvious metabolic
abnormalities and neurological symptoms.
 Depressive symptoms, if seen in CFS, may be differentially diagnosed from primary depression due to the absence of anhedonia,
decreased motivation, and guilt; and the presence of somatic symptoms such as sore throat, swollen lymph nodes, and exercise
intolerance with postexertional exacerbation of symptoms.

CHRONIC FATIGUE TREATMENT – Cont…..
 If you are suffering from chronic fatigue, you do not have to accept it, and live with it. There are treatments available
which can help. The treatment of chronic fatigue syndrome is basically treatments to relieve the symptoms:-
 Antidepressants: Many people who suffer from chronic fatigue are also suffering from depression. A mild
antidepressant will also help with your sleep, and relieve any muscle pain that you are experiencing due to the chronic
fatigue.
 Sleeping pills: Taking either an over the counter sleep aid, or having one prescribed by your doctor is a great way to
treat chronic fatigue. In taking a sleeping pill, you will be able to fall asleep faster, and stay asleep longer. This will
prevent the feeling of tiredness associated with fatigue.

 Start a bedtime routine: Going to bed at the same time every night will help with chronic fatigue. Also, you should avoid
napping.
 Avoid caffeine: Caffeine is a stimulant, which can make it a powerful force behind chronic fatigue syndrome. If you cut
the caffeine out of your diet, you will be more relaxed, & will be able to sleep better.
 Psychological counseling: By speaking with a counselor, you can discuss ways of coping with your chronic fatigue, so
that it does not create problems in your everyday life.

 Graded exercise: Inactivity is a major cause of chronic fatigue. By exercising more often, and doing ROM and stretching
exercises, you are becoming more active. These exercises need to be done in just a few minutes a day, and can make a
huge difference in your level of fatigue.
 Level out your activity: If you are having a good day, you do not want to go overboard with your level of activity. If you
overdo it on a good day, you will have many more bad days.
 Reduce stress: It is a great way to treat chronic fatigue. If you find yourself getting overwhelmed, you should step back,
calm down, and relax. There are many stress reduction techniques that you can try to keep your stress level down.

 Massage: Getting a nice massage is a great way to combat fatigue.
 Acupuncture: Acupuncture, a method of relieving the symptoms of several conditions through the use of needles, is a great way to
relieve the symptoms of chronic fatigue.
 Yoga: Yoga will not only add some activity into your daily routine, it is also a very relaxing way to be more active. This can have a great
impact on your level of fatigue.
 Anti fatigue mats: Anti fatigue mats are made to reduce fatigue that is used when standing or sitting on hard surfaces for long periods
of time. These mats can be made of rubber, vinyl, carpeting, and wood.

MUSCLE FATIGUE
 Muscle fatigue or physical fatigue is the decline in ability of a  muscle to generate force.
 It can be a result of vigorous exercise but abnormal fatigue may be caused by barriers to or interference with the
     different stages of muscle contraction.
There are two main causes of muscle fatigue :-
1. The limitations of a nerve’s ability to generate a sustained signal (Nervous Fatigue) &
2. The reduced ability of the muscle fiber to contract (Metabolic Fatigue).

NERVOUS FATIGUE
 Nerves are responsible for controlling the contraction of muscles, determining the number, sequence and force of
muscular contraction.
 In novice strength trainers, the muscle's ability to generate force is most strongly limited by nerve’s ability to
sustain a high-frequency signal.
 After a period of maximum contraction, the nerve’s signal reduces in frequency and the force generated by the
contraction diminishes.
 There is no sensation of pain or discomfort, the muscle appears to simply ‘stop listening’ and gradually cease to
move, often going backwards. As there is insufficient stress on the muscles and tendons, there will often be no
delayed onset muscle soreness following the workout.

METABOLIC FATIGUE
 Metabolic fatigue is a characteristic muscle response to intense exercise that has outstripped the rate of ATP
replacement.
 It is a common term for the reduction in contractile force due to the direct or indirect effects of two main factors:-
1. Shortage of fuel (SUBSTRATES) within the muscle fiber.
2. Accumulation of substances (METABOLITES) within the muscle fiber, which interfere either with the release of
calcium (Ca2+
) or with the ability of calcium to stimulate muscle contraction.

METABOLIC FATIGUE – Cont….
1. SUBSTRATES
Substrate within the muscle generally serve to power muscular contractions. They include molecules such as adenosine
triphosphate (ATP), Glycogen & Creatine phosphate (CP).
Adenosine triphosphate (ATP) binds to the myosin head and causes the ‘ratchetting’ that results in contraction
according to the sliding filament model.

METABOLIC FATIGUE – Cont…..
Glycogen is the intramuscular storage form of glucose, used to generate energy quickly once intramuscular creatine
stores are exhausted, producing lactic acid as a metabolic byproduct.
Creatine phosphate stores energy so that ATP can be rapidly regenerated within the muscle cells from ADP & inorganic
phosphate ions, allowing for sustained powerful contractions that last between 5–7 seconds.
Substrates produce metabolic fatigue by being depleted during exercise, resulting in a lack of intracellular energy
sources to fuel contractions. In essence, the muscle stops contracting because it lacks the energy to do so.

2. METABOLITES
Metabolites are the substances (generally waste products) produced as a result of muscular contraction. They include: -
Chloride
Potassium
Lactic Acid etc….
Accumulation of metabolites can directly or indirectly produce metabolic fatigue within muscle fibers through
interference with the release of calcium from the sarcoplasmic reticulum or reduction of the sensitivity of contractile
molecules actin & myosin to calcium.

 CHLORIDE
 Intracellular chloride partially inhibits the contraction of muscles.
 It prevents muscles from contracting due to "false alarms", small stimuli which may cause them to contract
(akin to myoclonus).
 This natural brake helps muscles respond solely to the conscious control or spinal reflexes but also has the effect of
reducing the force of conscious contractions

 POTASSIUM
 High concentrations of potassium also causes the muscle cells to decrease in efficiency, causing cramping and fatigue.
 Potassium builds up in the t-tubule or transverse tubule (It is a deep invagination of the sarcolemma; it present in
plasma memb. Of skeletal & Cardiac muscle) system and around the muscle fiber as a result of action potentials.
 The shift in K+
changes the membrane potential around the muscle fiber.
 The change in membrane potential causes a decrease in the release of calcium from the sarcoplasmic reticulum.
 Normal potassium level in the blood is 3.5-5.0 mEq/L.
Note: mEq/L = milliEquivalents per liter.

 LACTIC ACID
 Lactic acid is mainly produced in muscle cells and red blood cells. It forms when the body breaks down carbohydrates
to use for energy during times of low oxygen levels.
 Lactic acid as a waste product that causes fatigue and muscle soreness.
 The assumption was lactic acid had a "pickling" effect on muscles, inhibiting their ability to contract.
 The impact of lactic acid on performance is now uncertain, it may assist or hinder muscle fatigue.
Normal Range of Lactic Acid : -
1. Venous Blood: 0.5-2.2 mmol/L.
2. Arterial Blood: 0.5-1.6 mmol/L
Note: - mmol/L = millimoles per liter.

 LACTIC ACID – Cont…..
Abnormal Results:-
Abnormal results mean that body tissues are not getting enough oxygen. Conditions that can increase lactic acid levels
include:-
 Heart failure
 Liver disease
 Lung disease
 Not enough blood containing oxygen getting to a certain area of the body
 Severe infection that affects the entire body (sepsis)
 Very low levels of oxygen in the blood (hypoxia)

 LACTIC ACID – Cont…..
 Produced as a by-product of fermentation, lactic acid can increase intracellular acidity of muscles. This can lower the
sensitivity of contractile apparatus to Ca2+
but also has the effect of increasing cytoplasmic Ca2+
concentration through
an inhibition of the chemical pump that actively transport calcium out of the cell.
 This counters inhibiting effects of potassium on muscular action potentials. Lactic acid also has a negating effect on
the chloride ions in the muscles, reducing their inhibition of contraction and leaving potassium ions as the only
restricting influence on muscle contractions, though the effects of potassium are much less than if there were no
lactic acid to remove the chloride ions. Ultimately, it is uncertain if lactic acid reduces fatigue through increased
intracellular calcium or increases fatigue through reduced sensitivity of contractile proteins to Ca2+
.

METABOLIC BY-PRODUCTS AND FATIGUE
 Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
.
 Cells buffer H+
with bicarbonate (HCO3
–
) to keep cell pH between 6.4 and 7.1.
 Intercellular pH lower than 6.9, however, slows glycolysis and ATP production.
 When pH reaches 6.4, H+
levels stop any further glycolysis and result in exhaustion.

Physiology of fatigue

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