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بسم الله الرحمن الرحيم. Skeletal Muscle Metabolism and Fiber Types. Dr.Mohammed Sharique Ahmed Quadri Assistant Professor, Physiology. Contraction-Relaxation Steps Requires ATP muscle has been called "a machine for converting chemical energy into mechanical work.".

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Skeletal muscle metabolism and fiber types

بسم الله الرحمن الرحيم

Skeletal Muscle Metabolismand Fiber Types

Dr.Mohammed Sharique Ahmed Quadri

Assistant Professor, Physiology

Skeletal muscle metabolism and fiber types
Contraction-Relaxation Steps Requires ATPmuscle has been called "a machine for converting chemical energy into mechanical work."

Contraction relaxation steps requiring atp
Contraction-Relaxation Steps Requiring ATP

  • Splitting of ATP by myosin ATPase provides energy for power stroke of cross bridge

  • Binding of fresh molecule of ATP to myosin lets bridge detach from actin filament at end of power stroke so cycle can be repeated

  • Active transport of Ca2+ back into sarcoplasmic reticulum during relaxation depends on energy derived from breakdown of ATP

Energy sources for contraction
Energy Sources for Contraction

  • Transfer of high-energy phosphate from creatine phosphate to ADP

  • Oxidative phosphorylation (citric acid cycle and electron transport system

  • Glycolysis

Creatine phosphate

creatine kinase

Creatine phosphate + ADP creatine + ATP

  • First source for supplying additional ATP when exercise begins .

  • First few minute or less of exercise

  • Supports short burst of high intensity contractile efforts

  • source of creatine in diet , MEAT

Oxidative phosphorylation
Oxidative phosphorylation

  • In muscle mitochondria if sufficient O2 is present

  • Relatively slow – many steps involved

  • Supports aerobic ( with O2) or endurance-type exercise

  • Adequate O2 & nutrients required

  • Fueled by glucose or fatty acids depending upon intensity and duration of activity

    • Rest / light exercise – Fatty acids

    • High intensity exercise – Glucose


  • When O2 delivery or Oxidative phosphorylation can not keep pace with the demand for ATP

  • Advantage

    • Produce ATP in absence of O2

    • Much faster than oxidative phosphorylation

    • Supports anaerobic or high-intensity exercise

    • Disadvantage

      • Depletion of nutrient /energy reserve

      • Production of lactate


  • Contractile activity in a muscle can not be maintained at given level indefinitely

  • Fatigue

    • Muscle fatigue

    • Central fatigue

Muscle fatigue
Muscle Fatigue

  • Exercising muscle can no longer respond to stimulation with same degree of contraction

  • Defense mechanism that protects muscle from reaching - (rigor mortis)

  • Underlying causes of muscle fatigue are unclear

    • Local increase in ADP & inorganic phosphate

    • Accumulation of lactate

    • Accumulation of extracellular K+

    • Depletion of glycogen energy reserve

Central fatigue
Central Fatigue

  • Occurs when CNS no longer adequately activates motor neurons supplying working muscles

  • Often psychologically based

  • Mechanisms involved in central fatigue are poorly understood

    Neuromuscular fatigue: inability of motor neuron to synthesize acetylcholine- possible only experimentally

The oxygen debt mechanism
The Oxygen Debt Mechanism

  • After a period of exertion is over, extra O2 is consumed to

    • Remove the excess lactate

    • Replenish the ATP and phosphorylcreatine stores

    • Replace the small amounts of O2 that have come from myoglobin.

Major types of muscle fibers
Major Types of Muscle Fibers

  • Classified based on differences in ATP hydrolysis and synthesis

  • 3 major types

    • Slow-oxidative (type I) fibers

    • Fast-oxidative (type IIa) fibers

    • Fast-glycolytic (type IIx) fibers


  • Human physiology by Lauralee Sherwood, 7th edition

  • Text book physiology by Guyton &Hall,12th edition

  • Text book of physiology by Linda .s contanzo,third edition