Factors affecting muscle force

Question 1

What is the definition of tension?

Answer 1

The force that a muscle exerts on an object when it is contracting

Question 2

What is the definition of load?

Answer 2

The force that is exerted on a muscle by an object

Question 3

What must be the relationship between muscle tension and load in order for concentric contraction to occur?

Answer 3

The muscle tension generated must be greater than the load in order for muscle fibres to shorten and object responsible for the load to move

Question 4

What must be the relationship between muscle tension and load in order for eccentric or isometric contraction to occur?

Answer 4

The muscle tension must not exceed the load, such that the muscle fibres or remain the same length

Question 5

What is concentric contraction?

Answer 5

Aka isotonic contraction, where the muscle shortens under a constant load

Question 6

What is eccentric contraction?

Answer 6

Where the muscle length increases, and load is greater than tension

Question 7

What is isometric contraction?

Answer 7

Where the muscle length remains constant. When the object is free, load is equal to tension; when the object is fixed, load can be greater than or equal to tension

Question 8

Why is the latent period of isometric contraction much shorter than in isotonic contraction?

Answer 8

Because isotonic contraction needs to generate enough tension to overcome load; isometric latent period is related to tension, whilst isotonic latent period is related to distance shortened by

Question 9

With increasing load, what occurs to the single fibre contraction?

Answer 9

The latent period increases; velocity of shortening slows down; total duration of twitch became shorter; distance fibre is shortened by becomes less

Question 10

What is the relationship between load and velocity of isotonic contraction?

Answer 10

Increased load decreases shortening velocity until load is increased to point where muscle is unable to move, becoming isometric. When load increases above peak tension that muscle can produce, becomes eccentric contraction

Question 11

At what load point is isotonic contraction near maximum shortening velocity?

Answer 11

When there is no load

Question 12

What must the stimuli be like in order to create separate small tensions?

Answer 12

Stimuli must be separated by more time than total contraction time

Question 13

What occurs if a second stimulus is introduced halfway through contraction time, before muscle can fully relax?

Answer 13

Muscle tension rises further as more Ca2+ is in cell, meaning more tropomyosin is moved and more binding sites are available for actin and myosin to form cross-bridges and generate a stronger contraction

Question 14

What occurs if two stimuli happen very close together?

Answer 14

Higher tension is created, forming a smooth curve indicating summation

Question 15

What is summation?

Answer 15

Increase of muscle tension from successive action potentials

Question 16

What occurs if successive stimulation results in a sustained contraction?

Answer 16

A tetanus is formed

Question 17

What happens in an unfused tetanus?

Answer 17

Muscle fibre has time to partially relax before the next stimulation; development of tension oscillates

Question 18

What happens in a fused tetanus?

Answer 18

Muscle fibre has no time to relax; development of tension is continuous and smooth

Question 19

What is the length-tension relationship?

Answer 19

As the muscle length deviates higher or lower than optimal, force generation is low

Question 20

Why is force generation low when initial muscle length is less than optimal?

Answer 20

Actin filaments overlap with one another, so removes the potential of cross-bridges forming with one of the actin filaments (interfere with cross-bridges); Z-lines meet the ends of the myosin filament

Question 21

Why is force generation low when initial muscle length is more than optimal?

Answer 21

Fewer cross-bridges overlap actin molecules

Question 22

What are the three main sources of energy?

Answer 22

Creatine phosphate, oxidative phosphorylation, glycolysis

Question 23

What does creatine phosphate do?

Answer 23

Provides P very quickly to form ATP from ADP; lasts only for a short time

Question 24

Why is an oxygen debt?

Answer 24

The oxygen required to produce energy after exercise has finished in order to replenish stores of glycogen and CP, and remove lactate

Question 25

What are causes of muscle fatigue?

Answer 25

Conduction failure; lactic acid buildup; inhibition of cross-bridge cycling; fuel substrates; central command fatigue

Question 26

What is conduction failure?

Answer 26

Accumulation of K+ in t-tubules. Has a fast recovery

Question 27

Why does lactic acid buildup cause fatigue?

Answer 27

Acidic environment means proteins are not at optimum, and Ca2+ release and re-uptake mechanisms are interfered with

Question 28

Why does inhibition of cross-bridge cycling cause fatigue?

Answer 28

Accumlation of ADP and Pi in muscle fibres slows down cross-bridge cycling by preventing release of cross-bridges from actin molecules

Question 29

What fuel substrates can cause fatigue?

Answer 29

Muscle glycogen deficit, blood glucose deficit, dehydration

Question 30

What is central command fatigue?

Answer 30

Failure to propagate signals from the brain to motor neurons

Question 31

What are the three muscle fibre types?

Answer 31

Slow oxidative, fast oxidative, and fast glycolytic

Question 32

What are features of slow oxidative fibres?

Answer 32

Low ATPase activity, and highly oxidative

Question 33

What are features of fast oxidative fibres?

Answer 33

High ATPase activity, and highly oxidative/ moderately glycolytic

Question 34

What are features of fast glycolytic fibres?

Answer 34

High ATPase activity, and highly glycolytic