LECTURE 25

Question 1

How do muscles get injured?

Answer 1

Crushing, stretching, surgery, chemicals, lacerations, bleeding, contusion, ischaemia

Question 2

What muscle action results in the most injury?

Answer 2

Eccentric/lengthening/pliometric contraction

Question 3

What are examples of myotoxic injections?

Answer 3

Anaesthetic: bupivacaine

Snake Venom: notexin

Question 4

What is the sequence of muscle injury?

Answer 4

Degeneration, inflammation, regeneration, fibrosis

Question 5

Where are nuclei located in regeneration?

Answer 5

Centrally

Question 6

What is contraction?

Answer 6

Activation of muscle fibres with subsequent strong binding and cycling of cross-bridges and an attempt of sarcomeres to shorten

Question 7

What is the magnitude of force decrease associated with stretch induced injury determined by?

Answer 7

Average force developed during stretch and the displacement or magnitude of strain

Question 8

What are the indirect measures of muscle injury?

Answer 8

CK levels, calcium influx, maximum force, muscle soreness

Question 9

When do CK levels rise?

Answer 9

Mostly after eccentric exercise, response may be delayed and is variable between people

Question 10

What happens to CK levels after subsequent exercise?

Answer 10

Reduced - protective mechanism

Question 11

When can you begin to see the effects of muscle damage?

Answer 11

3 Days post exercise - inflammatory cells in muscle

Question 12

What provides the most valid measure of the totality of injury?

Answer 12

Change in muscle force

Question 13

What is initial injury?

Answer 13

The initiating event associated with contraction induced injury - mechanical - occurs when sarcomere are stretched excessively

Question 14

What is a focal injury?

Answer 14

Localised to a few sarcomere in series or parallel

Question 15

What is a widespread injury?

Answer 15

Across the entire cross section of the fibre

Question 16

What is the sarcomere inhomogeneity hypothesis?

Answer 16

• Length of sarcomeres isn’t uniform
• Injury occurs when weak sarcomeres are stretched by stronger sarcomeres that exist in series
• Weak sarcomeres randomly distributed, usually on descending limb of length tension curve
• When weak sarcomeres are stretched they pop and fail to reinterdigitate in relaxation

Question 17

What happens when there is massive shear stress?

Answer 17

Fibre ruptures

Question 18

What is secondary injury?

Answer 18

Occurs 1-3 days after initial injury, CK released, force deficit and loss of calcium homeostasis

Question 19

What is loss of calcium homeostasis?

Answer 19

Elevated calcium at site of damage, cellular necrosis (cal pains and caspases activated), SR becomes dysfunctional and can’t resequester calcium - injury may not progress to repair stage

Question 20

What happens if calcium levels are buffered adequately?

Answer 20

Cell will survive and local muscle repair will occur

Question 21

What happens if calcium levels are buffered inadequately?

Answer 21

Degradative enzymes will be activates, increased phospholipase and protease activity -regeneration inhibited

Question 22

Process of contraction induced injury?

Answer 22

• ejection of damaged components from fibre stimulates neutrophil accumulation
• viable fibre portions seal off
• neutrophils release degradative enzymes, increase blood supply, stimulate monocyte accumulation and activate satellite cells
• accumulated macrophages phagocytose debris and neutrophils and activate satellite cells

Question 23

When does vesicle clumping to buffer calcium occur?

Answer 23

Day 1

Question 24

What are the effects of repeat bouts of lengthening contractions?

Answer 24

Decrease force defecit

Question 25

What are trained muscles likely to have?

Answer 25

Increase sarcomere homogeneity, fibres are less likely to be pulled to descending limb of length tension relationship - less likely to be damaged