Fatigue, types of fatigue, physiology of fatigue, excitation-contraction coupling, fatigue during exercise

1. Fatigue
Dr. Shweta Kotwani; Pediatric Physical Therapist
BPTh (MUHS); MPT (Neuro,MUHS); LASHS-U.K.
Fellowship Dip.(Peds.Rehab.; Clinical Neuro.Sc.)

2. Excitation-Contraction
Coupling
 Excitation–contraction coupling is the
physiological process of converting an
electrical stimulus to a mechanical
response. It is the link (transduction)
between the action potential generated in
the sarcolemma and the start of a muscle
contraction .

4. Fatigue
 Fatigue is defined as the decrease in muscular
activity due to repeated muscle stimuli. When
stimuli are applied repeatedly, after sometime,
the muscle does not show any response to the
stimulus. This condition is called fatigue

5. Fatigue Curve
 When the effect of repeated stimuli is recorded
continuously, the amplitude of first two or three
contractions increases
 The force of contraction decreases gradually
 It is shown by gradual decrease in the amplitude
of the curves
 Just before fatigue occurs, the muscle does not
relax completely, it remains in a partially
contracted state. This state is called as
contraction remainder/ contracture

6. Fatigue during exercise
 Fatigue - inability to maintain a given exercise
intensity or power output
 Reversible with rest (recovery)
 rarely completely fatigued - can maintain lower intensity
output
 Studied with EMG and observation of contractile function
with electrical (nerve) or magnetic stimulation (cortex)
 Observe reduction in force and velocity and a prolonged
relaxation time after fatigue
 The effect of exercise at an absolute or relative
exercise intensity will be more severe on an
untrained individual

7. Causes
 Causes of muscle fatigue have been classified into
central and peripheral
 Central - includes CNS, motivation and psychological
factors
 restoration of force with external stimulation of muscle -
indicates central fatigue
 Accumulation of metabolites like lactic acidand phosphoric
acid, hypoglycemia, reticular formation
 Lack of oxygen
 Peripheral - PNS to muscle - EC coupling, energy
supply and force generation

8. Site (seat) of fatigue
 NMJ is the first seat of fatigue
 Second seat of fatigue is muscle
 Nerve cannot be fatigued
 Other sites include: pyramidal cells in
cerebral cortex, AHC (motor neurons)
of spinal cord

9. Types Of Fatigue

10. Central Fatigue
 CNS- initiation of motor patterns in motor cortex-
reduces
 Propagation of impulses down descending
motor pathways- excitation of alpha motor
neurons- resulting in recruitment of motor unit
 Central fatigue is inability to fully recruit all motor
units during isometric contraction.
 Lack of adequate CNS drive to working muscles.

12. Mechanism
Due to physiological changes-
 Decreased glycogen stores
 Decreased BCAA concentration
 Increased blood level of FFA
 Free tryptophan and serotonin
 When glycogen stores are depleted during
exercise there is increased utilisation of FFA &
BCAA as an energy source

13.  FFA and tryptophan are transported in the blood
attached to same carrier (ALBUMIN), increased
FFA levels will displace albumin bond tryptophan
and increase the concentration of free
tryptophan

14. Peripheral Fatigue
 Sites – sarcolemma, t-tubular system, sarcoplasmic
reticulum, actin myosin cross bridges
 Mechanism
Depletion of substrates
Creatine phosphate and glycogen undergo substantial
depletion during exercise
Anaerobic exercise for 30 secs lead to decrease in muscle CP
by 70%, glycogen store by 30%, ATP by 40-50%
Accumulation of metabolites

16.  Fatigue in multiple sclerosis: Mechanisms, evaluation and treatment,
PMC, 2010 Aug
Among patients with multiple sclerosis, fatigue is the most commonly reported
symptom, and one of the most debilitating.
Fatigue is considered to be one of the main causes of impaired QOL among
MS patients; reported by at least 75% of MS patients
Fatigue rating scales-
1. The Chalder Fatigue Scale (The Fatigue Scale)
 Also referred to as the FRS (fatigue rating scale), the Chalder Fatigue
Scale and the FS, this scale was developed for hospital and community
studies of patients with CFS and has been used in this population in many
studies. The FQ consists of 11 items measuring fatigue- related symptoms
and loading onto two dimensions— physical and mental fatigue. The
scale has good clinical validity supported by a population study of fatigue
in the general population.
 The validity of the FQ in assessing fatigue in the general population
suggests that it is a useful tool for assessing fatigue in a variety of medical
disorders, although the presence of primary physical or cognitive
dysfunction may confound interpretations of the responses

17. 2. Krupp’s Fatigue Severity Scale (FSS)
Fatigue severity scale has been shown to differentiate
between subgroups of patients with MS, CFS and primary
depression.
3. The Modified Fatigue Impact Scale (MFIS)
MFIS, proposed by the Multiple Sclerosis Council for Clinical
Practice Guidelines, has gained recognition among MS
specialists as a reliable tool. MFIS contains 21 items and
offers multidimensional assessment: physical (pMFIS:9
items), cognitive (cMFIS: 10 items) and psychosocial
functioning (psMFIS: 2 items)

18.  The assessment of fatigue
A practical guide for clinicians and researchers
 Journal of Psychosomatic Research 56 (2010) 157–170
 Visual Analogue Scale for Fatigue
The VAS-F was designed to be a simple and quick measure of fatigue
and energy levels for patients in the general medical population. It has
been found sensitive to morning and evening changes in cancer
patients.
 Fatigue severity scale (FSS)
 This is one of the best known and most used fatigue scales. The FSS
principally measures the impact of fatigue on specific types of
functioning rather than the intensity of fatigue-related symptoms.
 The FSS has high internal consistency, has good test– retest reliability
and is sensitive to change with time and after treatment. It also has good
concurrent validity and is able to distinguish patients with different
diagnoses (be- tween systemic lupus erythematosus (SLE) and MS
between CFS, MS and primary depression ]. In a comparison of the FSS
and the Fatigue Questionnaire (FQ) in a sample of CFS patients, the
FSS was found to be the more effective measure, probably owing to its
specificity to the behavioural consequences of fatigue.

19. Effects of Low-Level Laser Therapy (LLLT) in the Development of
Exercise- Induced Skeletal Muscle Fatigue and Changes in
Biochemical Markers Related to Post-exercise Recovery
august 2010 | volume 40 | number 8 | journal of orthopaedic &
sports physical therapy
 Nine healthy male volleyball players participated in
the study. They received either active LLLT (cluster
probe with 5 laser diodes; λ
= 810 nm; 200 mW power output; 30 seconds of
irradiation, applied in 2 locations over the biceps of
the nondominant arm; 60 J of total energy) or
placebo LLLT using an identical cluster probe. The
intervention or placebo were applied 3 minutes
before the performance of exercise. All subjects
performed voluntary elbow exion repetitions with a
workload of 75% of their maximal voluntary
contraction force until exhaustion.

20.  Conclusion: Pre-exercise irradiation of the biceps
with an LLLT dose of 6 J per application location,
applied in 2 locations, increased endurance for
repeated elbow flexion against resistance and
decreased post-exercise levels of blood lactate,
creatine kinase (CK), and C- reactive protein (C-
RP).

21. THANK YOU