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FATIGUE

• Feeling of tiredness & lack of strength due to physical / mental strain or illness , which can be ameliorated through additional rest

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MUSCLE FATIGUE

• Any exercise induced reduction in the ability of muscle to generate force or power regardless of whether or not the task can be sustained

S C Gandevia , 2001

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NORMAL FATIGUE

• A state of general tiredness which is the result of overexertion & can be reversed by rest

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PATHOLOGICAL FATIGUE

• A state characterized by weariness unrelated to previous exertion levels & is usually not reversible by rest

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• Normal fatigue • Pathological fatigue

• Rapid onset

• Short duration

• Single identifiable cause

• Protective

• Gradual onset

• Long duration

• Multiple unknown causes

• Abnormal

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CHRONIC FATIGUE SYNDROME

• Abnormally excessive

• Unexplained

• Persistent for six months or more

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NEUROLOGICAL FATIGUE

• Subjective lack of physical or mental energy which is perceived by the individual or caregiver to interfere with usual & desired activities

MS council clinical practice guidelines

,1998

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Types of fatigue

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2 types :

1.Physical fatigue

2.Mental fatigue

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PHYSICAL FATIGUE

• Inability to exert force within one’s muscles to the degree that would be expected given the individual’s general physical fitness

Muscle weakness

True weakness Perceived weakness

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Objective weakness

A condition where the instantaneus force exerted by the muscle is less than that would be expected

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Subjective weakness

A condition where it seems to the patient that more than normal effort is required to exert a given amount of force

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Enhanced perception of limited endurance of sustained mental activities

Manifests as somnolence or just decrease of attention

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Mental stress

Lack of sleep

Depression

Chemical causes04/08/23 16

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Reduction in the ability of muscle to perform work because of impairment anywhere along the command from neuromuscular transmission to the actin – myosin cross bridging

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Peripheral model assumes fatigue at one or more sites which initiates muscle contraction

Therefore dependent on the localized chemical conditions of the muscles

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Depletion of energy substrates Aerobic metabolism Anaerobic

metabolism

Change in intracellular ion levels leak of calcium ions

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Decline in force output due to reduction in the neural drive or nerve based motor commands to the working muscles

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Protective phenomenon

Works to preserve the integrity of system by initiating muscle fatigue through muscle decruitment

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Failure in integration of limbic input & the motor functions within basal ganglia

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TNF-ALPHA INTERLEUKIN – 6

Metabolic abnormalities of frontal cortex & basal ganglia

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Hypofunctioning

Reduced Cortisol secretion

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Increased level of serotonin in brain during exercise , peak at fatigue

Effects on arousal , lethargy , sleepiness & mood

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Change in the force response to electric stimulation during rest following exercise relative to pre stimulation force

Reveals any loss of force in the muscle tissue after constant activation

Decline in force reflects the severity of fatigue

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Rest twitches before & after MVC

Attenuation of post stimulation twitches indicate peripheral fatigue

Dominant slowing of the relaxation phase

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Changes in sarcolemma

Variables : Amplitude Frequency Muscle fiber conduction velocity

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Amplitude increases during submaximal exercise

During high contraction , amplitude declines

Change in frequency spectrum & MFCV

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MVC + Electrical stimulation to motor end plate

Increased exertion of force demonstrates Central Activation Failure

The technique allows quantification of CAF

Can’t differentiate between various central causes

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Magnetic & electrical stimulation of motor cortex

Artificially activates CNS

Response is measured at output site

Studies reported diminished output after fatiguing contraction

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Responses following magnetic stimulation are often submaximal

Any change in motor output is interpreted as change in excitability of motor cortex as induced by stimulus

Not the actual diminished voluntary drive

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Negative movement related cortical EMG potential over the scalp 1 sec before a self paced motor act

Generated by supplementary motor area & primary motor cortex

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During high force voluntary contraction , RP increases

Provides measure to determine changes at the motor cortex level instead at the output site

Does not require artificial stimulation

Prominent tool to study central changes during natural repetitive contractions

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70 % of patients with MS

Present even at rest

Both physical & cognitive components

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Worsened by stress & increase in temperature

No correlation with age, neurological impairment , sleep disturbance

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25 % - 92 % of stroke survivors

Persists despite excellent neurological recovery

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Tends to decrease with time

Independent of stroke severity, localization or functional impairment

Correlation with brainstem or thalamic stroke

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Incidence – 40%

Related to Dopamine deficiency

Levodopa normalizes cortical motor neuron excitability

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Muscle weakness – the commonest symptom

Metabolic / mitochondrial disorders : Fatigue

Exercise intolerance

Weak atrophic muscles functioning at their limits metabolically

Energy supply fails because of metabolic compromise

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Abnormal rise in sEMG potential

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Reported by 25- 40 %

Post encephalitic damage

Reticular Activating System

Dopaminergic neurons in Substantia Nigra

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Manifests at the onset

Persists for months regardless of full recovery of PNS

Central fatigue component

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To ascertain whether normal or pathological

To identify possible predisposing factors

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Onset

Duration

Severity

Daily pattern

Aggravating / Relieving factors

Impact on daily living

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9 item measure

7 point likert scale format

Ranges from : 1 ( strongly disagree) 7 ( strongly agree)

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1. My motivation is lower when I am fatigued.2. Exercise brings on my fatigue.3. I am easily fatigued.4. Fatigue interferes with my physical functioning.5. Fatigue causes frequent problems for me.6. My fatigue prevents sustained physical

functioning.7. Fatigue interferes with carrying out certain duties

and responsibilities.8. Fatigue is among my three most disabling

symptoms.9. Fatigue interferes with my work, family or social

life 

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Total score - Mean score across the 9 statements

FSS score > 4 : Severe fatigue

Most widely used measure in neurological conditions

Able to differentiate between patients & healthy subjects

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High validity

Internal consistency ( cronbach alpha = 0.81 – 0.95 )

Test retest reliability ( 0.8 ) in patients with MS & Polyneuropathies

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Modification of VAS for pain

Scores range from : 0 (no fatigue) to

10 ( worst fatigue )

VAS score > 4.4 : Severe fatigue

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Simple , practical , reproducible & fast to apply

Used to measure fatigue changes over time intervals (minutes, hours )

To closely estimate average intensity changes over longer time period ( weeks , months )

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4 statements

7 point likert scale

Total score = mean score of the 4 statements

Able to differentiate between patients & healthy subjects

Internal consistency ( cronbech alpha = 0.81)

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Developed for patients with MS

40 independent symptom based questions

Scale of : “ 0 (no problem )” to

“ 4 ( extreme problem)”

Total score = Sum of responses to all 40 entries

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Minimum score = 0 ( No fatigue)

Maximum score = 160 ( Extreme fatigue)

FIS score of 80 or higher correlates with moderate to severe fatigue

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Energy category - one of the 6 categories of NHP

Consists of 3 yes / no questions

Total score = no. of questions answered with yes *

100 total no. of questions

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0 ( No complaints ) 100 ( Answered yes to all

complaints )

Internal consistency ( Cronbach α = 0.71)

Test retest reliability (Spearman ρ = 0.77 – 0.86) in patients with stroke

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Fatigue scores are not interchangeable

Structure & attributes of questionnaire differ remarkably

Weight of individual components of fatigue contribute to significant interscale score deviation

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FSS : Asseses neuromuscular fatigue

VAS : No identifiable domains

FIS : Less emphasis on physical

fatigue More on emotional, cognitive

& social elements of fatigue 04/08/23 68

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Identification & optimum management of potential factors

Nutrition counselling

Drugs : Antidepressants Amantadine Modafinil

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Combination of cognitive & behaviour therapy approaches

Identification of unhelpful, anxiety provoking thoughts & challenges

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Stress management techniques : -

Relaxation Hypnosis Guided imagery Distraction

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Moderate intensity :

Aerobic training

Strength training

Flexibility training

Group therapy

Level II evidence

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Fatigue dairy

Restricting timing of daily activities

Prioritizing tasks

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Imp to make the patient aware that fatigue is real

Recognition by patients, caregivers & family members

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Goals :

To improve understanding in patients care giving

To involve patient, caregivers in setting goals, directing & evaluating the intervention

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Relaxation training

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Chinese technique of inserting needles into the body

Strengthen the vital essence of human body

Removes the blockage of channels

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S C Gandevia : Spinal and Supraspinal Factors in Human Muscle Fatigue .Physiological Reviews , 2001 ; 81 : 4

Abhijit Chaudhuri, Peter O Behan :Fatigue in neurological disorders ; The Lancet ; 2004 ; 363, 20

Marloon groot et al : Fatigue associated with stroke and other neurologic conditions: implications for stroke rehabilitation Archives of Physical Medicine and RehabilitationVolume 84, Issue 11, November 2003, Pages 1714-1720

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M J Zwartz : Clinical neurophysiology of fatigue ; Clinical neurology , 119 , (2008), 2-10

William s, B Krupp : Multiple sclerosis related fatigue ; Phys Med Rehab Clin N Am , 16 (2005) , 483

Physiolological Basis Of Movement : Latash

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