Skeletal Muscles 2 - contractile properties

isometric conctration

muscle is exerting force but muscle length doesn’t change e.g warrior pose

• while myosin head is grabbing actin, actin is being pulled in another direction

when does isometric contraction occur

muscle force generated is equal or less than the external load = muscle can’t move object

maximum isometric force

highest peak force muscle generates without changing length

concentric contraction

muscle shortens as generates enough force to move external load

phases of concentric contraction

1. force increases without shortening bc building up enough to overcome load

2. muscle shortens = moves load without generating additional force

force velocity relationship

lower force = faster muscle contracts

power

rate force is applied over time

• power = velocity x force

When trying to lift a weight off a platform, just as muscle begins to contract the platform is removed. What happens?

can’t tell bc muscle force and actual weight is unknown. 3 possibilities

1. if weight = force the weight won’t move

2. weight exceeds force = dropped

3. force exceeds weight = lifted

eccentric contraction

muscle slowly lengthens while still exerting force

• external load is greater than force

which contraction type causes the most damage

eccentric

• fewer fibres are activated = more strain

• individual sarcomeres can be over-stretched as forcibly stretched while trying to contract

role of joints in muscle contractions

acts as pivot points for bones to rotate when muscles contract

antagonist muscle group

set of muscles that oppose the actions of another muscle

• skeletal muscles only pull never push = arranged in pairs around joints

when 2 muscles (muscle A is smaller) around a joint are activated what will happen?

can’t tell bc activation level is unknown

• number of motor units recruited determines strength of contraction

If a long, thin muscle arrangement and short wide arrangment have identical individual sarcomeres (same number, force and speed) which arrangement generates highest velocity?

long thin bc sarcomeres arranged end-to-end (like a train) so shorterning of each sarcomere is added together. For wide sarcomeres are stacked so velocity is seen as shortening of 1 sarcomere

If a long, thin muscle arrangement and short wide arrangment have identical individual sarcomeres (same number, force and speed) which arrangement generates greatest force?

short wide bc stacked arrangement means larger cross sectional area = individual forces of sarcomeres are added together. For thin sarcomeres share the same force

relationship between velocity and muscle length

velocity is proportional to muscle length

relationship between force and cross sectional area

force is proportional to cross sectional area

If a long, thin muscle arrangement and short wide arrangment have identical individual sarcomeres (same number, force and speed) which arrangement generates greatest power?

Same amount is generated bc power = velocity x force

relationship between power and muscle arrangement

different muscle arrangements can generate the same amount of power but at different velocities

can power be increased?

yes by increasing muscle size (increases CSA) and/or increasing muscle velocity

how could muscle velocity be increased

converting short twitch fibres into fast twitch fibres

For a bicep curl using weight, at which stage would bicep exert most force? 1. initial lift from extended position 2. middle of lifting (135°) 3. finished locked position

middle due to optimal length principle

optimal length principle

skeletal muscle generates max force at mid-range length due to perfect overlap between myosin and action

• stretched muscle = sarcomeres stretched = myosin interacts with few actin

• short muscle = actin filaments overlap each other = myosin interacts with less actin

• mid-range = max number of cross-bridges. more cross-bridges = more force