Skeletal Muscle Physiology

Front 1

twitch

Back 1

single, sudden muscle contraction lasting a fraction of a second

Front 2

isometric

Back 2

contraction without shortening

Front 3

isotonic

Back 3

a shortening contraction where the tension in the muscle remains constant. These are normally rare or short-lived events.  Often referred to in biomechanics as a shortening contraction with a constant load.

Front 4

isokinetic

Back 4

a contraction at a constant speed (typically with varying load)

Front 5

concentric

Back 5

shortening contraction

Front 6

eccentric

Back 6

a force producing contraction that occurs while a muscle is lengthening

Front 7

agonist

Back 7

the muscle responsible for a specific movement

Front 8

antagonist

Back 8

a muscle that opposes the movement of an agonist

Front 9

coactivation

Back 9

simultaneous contraction of antagonistic muscles on opposite sides of the joint

Front 10

Latent period

Back 10

time from the signal to initiate contraction to the point when muscle tension starts to build - membrane depolarization and release of calcium

Front 11

Peak twitch tension

Back 11

a force usually = 15-25% of max. isometric tension

Front 12

summation

Back 12

next contraction starting before the previous one is over

Front 13

tetanization

Back 13

summation to the point that contractions fuse together

Front 14

size principle

Back 14

- a weak contraction is obtained from motor units with the smallest and fewest muscle fibers
- a stronger contraction is obtained from motor units with larger and more numerous muscle fibers

Front 15

staircase effect

Back 15

strength of successive contractions increase (to a plateau) probably due to accumulating calcium, and enzyme systems getting more efficient as muscle warms up