exercise induced muscle damage

Question 1

what causes muscle soreness

Answer 1

pain sensitive receptors (afferent neurons) are repsonsive to mech deformation and intramuscular metabolic disturbance
- fibres project to the CNS and promote the sensation of pain

Question 2

what does eccentric exercise cause

Answer 2

decreased force output
highest soreness after first bout
- second bout = less soreness and less decrease in force output

Question 3

what is the benefit of RBE

Answer 3

ability of the muscle to rapidly adapt to the damage from eccentric exercise to prevent further damage

Question 4

what are the events leading to muscle damage from eccentric exercise

Answer 4

• overstretch of a muscle
• disrupted sarcomeres
• EC coupling disruption
• local contracture (increase in passive tension)
• swelling and soreness

Question 5

what is sarcomere inhomogeneity

Answer 5

weaker sarcomeres are stretched beyond myofilament overlap
most of the length is taken by weakest half sarcomeres in myofilament

Question 6

what is the popping sarcomere hypothesis

Answer 6

uncontrolled extension of individual half sarcomeres in each myofibril
- occurs one at a time - weakest to strongest
each sarcomere is stretched until half sarcomere is popped
- passive tension (titin) is able to support the sarcomere integrity until further stretch damages the titin as well

Question 7

what is EC coupling disruption

Answer 7

t-tubule rupture releases calcium
torn tubule ends leads to inactivation of some sarcomeres
results in fall in muscle tension and force output
- entire EC coupling is disrupted due to muscle damage ((t-tubules and SR)

Question 8

what is involved in local contracture (increase in passive tension)

Answer 8

rise in passive tension after eccentric exercise
muscle length is shorter and becomes stiff
increased stiffness = reduced ROM = reduced joint angle
peaks around 48-72 hours after exercise

Question 8

what are the potential mechanisms for increase in passive tension

Answer 8

• increases in resting Ca2+ levels in muscle fibres due to damage
• shortening of parallel, non contractile elements in the muscle (titin)

Question 9

what is the pain experienced during muscle contraction after eccentric exercise related to

Answer 9

1. damage and shortening of the non contractile elements (muscle mechanical stiffness)
2. damage to muscle fibre membranes (shown by an increase in CK enzyme)
   - can be measured by blood draw
   - shows a huge spike in CK around 48-72 hours
3. activation of group III/IV afferents

Question 10

what is RBE

Answer 10

magnitude of muscle damage is attenuated in a subsequent exercise bout after performing a single bout of exercise
- less swelling of muscle
- smaller increases in CK
- less abnormalities in muscle structure in imaging

Question 11

what is responsible for RBE

Answer 11

adaptations of muscle fibres and/or connective tissue
- neural adaptations are not totally discarded

Question 12

how long does RBE last

Answer 12

literature - 6-9 months based on the magnitude of muscle damage in initial bout
- doesn’t make sense in real life

Question 13

what are the mechansims underlying RBE

Answer 13

neural
mechanical
cellular - longitudinal addition of sarcomeres

Question 14

how does the increase in sarcomeres in parallel occur

Answer 14

• eccentric contraction results in muscle damage
• contractions at longer muscle length = mroe damage + more symptoms
• addititonal sarcomeres in series created during the repair

Question 15

what changes with the increase in sarcomeres in parallel

Answer 15

shift in the length tension curve towards longer lengths
tension declines with increasing length (can be avoided)
- avoids sarcomere disruption (prevents further muscle damage/soreness)

Question 16

what is the shift in optimum length

Answer 16

total tension curve moves to the right with RBE
muscle can maintain greater tension at the same length with an increase in sarcomeres in series