Topic 21 - Length - tension diagram: working range and power of the muscle; heat production and muscle fatigue

Question 1

Words to include in Length-tension diagram: working range and power of the muscle

Answer 1

• Length-tension diagram
• Stretch
• Work
• Passively stretched muscle
• Sarcomer
• Isotonic condtions
  
  • Isotonic maximum curve
  • Passively stretch muscle
• Isometric conditions
  
  • Isomteric maximum curve
  • Shortening (ø)
• Preload experiment
  
  • Preload-maximum curve
  • Tension (↑)
  • Contraction
• Afterload experiment
  
  • Afterload-maximum curve
  • Shortening
  • Tension (↑)
• Working range of the muscle
  
  • Physological working range
  • Skeletal muscle
  • Cardiac muscle
• Velocity/tension relationship
  
  • Power
  • Muscle contraction
  • Unloaded muscle
  • Overloaded muscle
  • Phasic muscle
    
    • Fast
  • Tonic muscle
    
    • Slow
  • Velocity-tension diagram
    
    • Power of the muscle
  • Optimal position
    
    • Intermediate load

Question 2

Words to include in heat production

Answer 2

• Work
• Contraction
  
  • ATP breakdown
  • Synthetic process
• Phasic fibers
  
  • Fast
  • White
  • Restitution
• Tonic fibers
  
  • Slow
  • Red
  • Contraction
• Resting
  
  • Muscle tonicity
  • BMR (Basal Metabolic Rate)
• Initial heat production
  
  • Electro mechanical coupling
    
    • Activation heat
      
      • Ca²⁺ release
      • Myosin activation
    • Contraction heat
      
      • Sliding filament mechanism
      • Ca²⁺ repumping
• Restitution heat
  
  • Phasic muscles
    
    • Fast
    • White
    • Anaerob
    • Glycolytic
  • O₂-debt
  • ATP resynthesis
  • Restitution

Question 3

Words to include in fatigue of the muscle

Answer 3

• Fatigue
• Ratio
  
  • Glycolytic fibers
  • Oxidative fibers
• Metabolic by-products (↑)
• Mechanogram
• Twitch amplitude (↓)
• Twitch duration (↑)
• In vitro fatigue
  
  • Transmitters (ø)
    
    • N₂-rich environment
  • Oxygen (ø)
• In vivo fatigue
  
  • Peripheral fatigue
    
    • Energy stores (↓)
    • By-product concentration (↑)
    • Lactic acid
  • Central fatigue
    
    • Long term tension
    • Motor unit
    • Myoneural junction
• Heat production (↑)
• pH (↓)
• Lactic acid
• Dehydration
• Hypoglycemia
• Red fibers
• Total muscle
• White fiber
• Tension kg/cm²
• Time

Question 4

Topics to include in the essay

Answer 4

1. Lenght-tension diagram
   
   • Isotonic conditions
   • Isometric conditions
   • Preload experiment
   • Afterload experiment
   • Physological working range of the muscle
2. Velocity-tension relationship
3. Heat production
   
   • Phases
     
     • Resting
     • Initial heat production
     • Restitution heat
4. Fatigue of the muscle

Question 5

Lenght-tension diagram

General

Answer 5

• Each skeletal muscle is under a certain degree of stretch
  
  • Length X tension (load) = work
• Length-tension curve is obtained when stimulating the muscles with maximal single impulses
• The muscles are passively stretched with varying loads
• Physological working range of the muscle
  
  1. ​​Isotonic conditions
  2. Isometric conditions
  3. Preload experiment
  4. Afterload experiment

Figure: passively stretched muscle

Question 6

Length-tension diagram

Isotonic conditions

Answer 6

If we passively stretch the muscle to A, B, C distances above the resting length (L0) and in these positions we stimulate the muscle with maximal stimuli, we can obtain the isotonic maximum curve for that muscle

Question 7

Length-tension diagram

Isometric conditions

Answer 7

If no shortening is possible, we can measure the extent of the tension and get the isometric maximum curve

Question 8

Length-tension diagram

Preload experiment

Answer 8

• Tension increase is followed by contraction
• Result: preload-maximum curve

Question 9

Length-tension diagram

Afterload experiment

Answer 9

• Shortening, then tension increase
• Afterload-maximum curve

Question 10

Length-tension diagram

Working range of the muscle

Answer 10

• A summary of:
  
  • Isotonic conditions
  • Isometric conditions
  • Preload experiment
  • Afterload experiment
• Can construct the area of the physological working range of that muscle
• Muscle work in this range
• Skeletal muscle: length measure under maximal power = normal working range
• Cardiac muscle: normal working range is much below the length, which would ensure maximal tension

Question 11

Velocity-tension relationship

Answer 11

• Power
• A direct relationship can be seen between velocity of shortening and tension-parameters of muscle contraction
  
  • Tension is low (unloaded muscle) = velocity is high during contraction
  • Tension is high (overloaded muscle) = small velocity during contraction
• Velocity X tension = power
• Velocity related to an actual tension is determined by the type of the muscle:
  
  • Fast: phasic
  • Slow: tonic

​

• By drawing the velocity-tension diagram instead of the length-tension diagram, we could have an idea of the power of muscle
• Optimal position: under intermediate load can the muscle contraction be optimally fast

Question 12

Heat production

Answer 12

• Muscle produces heat during work:
  
  • During contraction: ATP breakdown
  • After contraction: synthetic process create heat
• Phasic (fast, white) fibers: produce more heat during restitution
• Tonic (slow, red) fibers: heat production mostly occurs during contraction

Question 13

Fatigue of the muscle

Answer 13

• Muscles are capable of long lasting activity. After a certain period, muscle become fatigued
• Fatigue depends on the ratio of glycolytic and oxidative fibers of the muscle
• Under physiological conditions
  
  • Not caused by: lack of transmitters or oxygen
  • It is: increasing concentration of metabolic by-products that cause the inability of concentration in muscles
• Signs of fatigue (both observable in mechanogram):
  
  • Twitch amplitude ↓
  • Twitch duration ↑
• In vitro fatigue
  
  • ​Ø O₂
  • Ø Transmitter
• In vivo fatigue
  
  1. ​Peripheral fatigue, a consequence of:
     
     • Energy stores ↓
     • By-product concentration ↑
     • Direct effect of lactic acid
  2. Central fatigue, after long term tension:
     
     • Exhaustion of motor unit
     • Exhaustion of myoneural junction
• Subjective feelings of fatigue:
  
  • Heat production ↑
  • pH ↓
  • Direct effect of lactic acid
  • Dehydration
  • General hypoglycemia

Figure: Fatigeu is developed earlier in fast, glycolytic, phasic fibers than in tonic, oxidative fibers