Skeletal Muscle Fatigue1111

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					             Rehabilitation Science Department
               Therapeutic Exercises
Course name: Physical therapy procedure II
Course code & number: 322 RHS
Lecture Name: Therapeutic exercises
Lectures Name: Dr. Ashraf Ramadan Hafez
Objective of Lecture:
After studying this lecture, the student must be able;
To define Skeletal Muscle Fatigue
To define Types of Skeletal Muscle Fatigue
To define causes Skeletal Muscle Fatigue
To define signs and symptoms
Content of lecture
Skeletal Muscle Fatigue
Causes of Fatigue
Types of fatigue
According to its incidence:
1- Acute muscle soreness
2-Delayed-onset muscle soreness:
According to its type:
1- Local muscle fatigue:
2- General muscle fatigue:
Signs and symptoms of fatigue
Recovery from fatigue

                                Skeletal Muscle Fatigue
   Muscles are impressive motors that respond rapidly to commands from the motor
nervous system. Skeletal muscle cells can increase their force production up to 40
N/cm2 in less than 100 ms. When unloaded they can shorten at a rate of up to ten
muscle lengths/s
   However, repeated activation of muscle cells leads to decreased force production
and slower contractions, that is, fatigue develops. Fatigue may set in acutely during
high-intensity exercise, and it is then mainly caused by factors related to increased
energy metabolism.
   Contractions that involve stretch of the muscle also cause muscle weakness and
damage, which takes many days to recover from. This also explains why exercising
long and hard enough to feel the burn for an extended period leaves your muscles sore
for one or more days afterwards. Athletes call this Delayed-Onset Muscle Soreness
   The skeletal muscle cells have to be used closer to their maximum capacity during
normal daily physical activities. Thus, while acute muscle fatigue only limits
performance during extensive activities (e.g, sport activities) in young healthy
subjects, it may severely hinder everyday physical activities in people with muscle
   For example, walking up stairs may require approximately 30% of the maximal
power output of a healthy subject, in a patient with muscle wasting and weakness,
approximately 90% of the maximal power output may be required, and fatigue will
then seriously affect the performance (the patient can no longer reach the top of the
Causes of Fatigue
1- The depletion of energy stores
- Physical activity for short time (several minutes) ---Energy used is glucose and
- Exercise for more than 90 minutes---decrease glycogen---decrease blood glucose
level---Decrease energy---more dependent upon fat---fat cannot be used to produce
e.g. marathon’s runners, hitting the wall.
2- the accumulation of inhibitory metabolic waste products
     • Accumulation of lactic acid making muscle more acidic--- inhibitory effect of
         the process of muscle contractility---burning sensation or pain within the
     • During prolonged forms of exercise the body will sweat to regulate body
         temperature---dehydration (reduce body fluid)---affect the efficiency of
         cardiovascular system---reduce oxygen supply to the muscle.
If the state of dehydration persists---sweating stops in order to conserve body fluid---
over Heating---impaired metabolic reactions---collapse, if not treated may be fatal.
4- neurological causes:
     • Depletion of acetylcholine at the neuromuscular junction or neurotransmitter
         at the synapses.
Types of fatigue
According to its incidence:
1- Acute muscle soreness: muscle pain develops during or after strenuous exercise
due to lack of adequate blood flow, oxygen and accumulation of lactic acid and
potassium in the exercised muscle. It is transient and subside quickly when adequate
blood flow and oxygen are resored to the muscle.
2-Delayed-onset muscle soreness:
Muscle tenderness and temporary stiffness develop 12-24 after exercise. This may be
due to microtruama to muscle fibers and/or connective tissues that results in tissues
According to its type:
1- Local muscle fatigue:
The diminished response of a muscle to repeated stimulus, due to decrease in the
amplitude of motor unit potential.
     - High or low intensity exercises applied.
     - Disturbance in the contractile mechanism due to decrease energy stores(
         insufficient oxygen and accumulation of lactic acid).
     - Inhibitory influence from CNS.
     - Pain and mucle spasm
2- General muscle fatigue:
  Is diminished response of a person during prolonged physical activity as walking.
1-decreased in blood glucose level
2-decreased in glycogen stores in muscle and lever.
3-depletion of potassium
4-dehydration due to prolonged form of exercise.
5-depletion of acetylcholine.
Signs and symptoms of fatigue
1-pain and muscle cramp
2-decrease in active motion
3-use of substitute motion
4-inability to continue low –intensity physical therapy
Recovery from fatigue
Adequate time for Recovery from fatigue must be built into every resistance training
in order to:
-Replenish energy stores
-Removal of lactic acid from the muscle
    - Replenish of oxygen store in the muscle
    - Replacement of glycogen

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