Chapter 9: SECTION B
Muscle Physiology attached, so the latent period is due only to the
Mechanics of Single Fiber Contraction excitation-contraction coupling delay
- In the isotonic twitch, the latent period includes:
2 opposing forces during muscle contraction: time of excitation-contraction coupling delay and
●Tension: force exerted by a contracting muscle a brief period of isometric contraction. During
●Load: force exerted by an object which, muscle can develop enough cross-bridge
cycling to enable the fiber to lift the load from the
Simple twitch contraction surface of an object.
● Event of muscle contraction as a parabolic
tracing- a curved graph; a single muscle contraction Load-Velocity Relation
of a single muscle fiber by a single stimulus. - Velocity: muscle shortening
- Increasing load = decreasing velocity of muscle
3 stages of contraction: fiber shortening
1. Latent period- a brief interval (1-2ms) of - Decreasing load = increasing velocity
assuming inactivity of the muscle fiber - No load = highest velocity
between the application of stimulus and the - Highest tension = no velocity
application of tension to the muscle;
corresponds to the time of excitation events Frequency-Tension Relation
that occur in the muscle prior to tension - 1 action potential in a muscle fiber lasts only
building. for 0.1-0.2secs
2. Contraction period- steep upward curve - Summation: possible to stimulate the muscle
from the pt. of tension development to the pt. to contract before its first contraction has
of peak tension development of the muscle finished; summated contraction
3. Relaxation period- downward curve; muscle - Unfused tetanus: incomplete summations
resume its original length - Treppe contractions: unfused tetanus in an
ascending manner; bladder-like contractions
3 main kinds of muscle contraction: (german); fundamental reason why we have to
(based on relative magnitudes of load and tension) warm up when we gauge in muscular activity;
● Isometric contraction we make calcium ions more available and at the
- Load > tension same time increase the # of myofibrils
- Muscle develops tension but does not shorten contracting w/ an increasing stimuli.
and move the load or object - Fused tetanus/summation: complete
- Shorter latent period* summation that produces a plateau of the
- Longer duration of mechanical event* contractions; does not go on indefinitely,
● Isotonic contraction produces a downward slope at one point
- Tension > load (muscle fatigue); even in continuous application
- Load or object is moved by the muscle of stimulus, no contraction can be made
- Longer latent period* anymore in the fatigued muscle; fatigued
- Briefer duration of mechanical event or muscle= loss of energy reserves or source
shortening* (ATP)
● Lengthening contraction:
- “eccentric contraction” Length-Tension Relation
- Load is much greater than what the maximum - The strength or tension that can be developed
isometric tension can develop; muscle stretches by a muscle can be changed by the length of
because load > max. isometric tension the fiber before contraction.
- 60% longer or shorter from the optimum
*Reason for this difference: length = no tension when stimulated
- In the isometric twitch, tension begins to - Increase length from this point = active
increase as soon as the first cross-bridge is isometric tension @ each length is increased
up to a maximum optimum length
Muscle Physiology attached, so the latent period is due only to the
Mechanics of Single Fiber Contraction excitation-contraction coupling delay
- In the isotonic twitch, the latent period includes:
2 opposing forces during muscle contraction: time of excitation-contraction coupling delay and
●Tension: force exerted by a contracting muscle a brief period of isometric contraction. During
●Load: force exerted by an object which, muscle can develop enough cross-bridge
cycling to enable the fiber to lift the load from the
Simple twitch contraction surface of an object.
● Event of muscle contraction as a parabolic
tracing- a curved graph; a single muscle contraction Load-Velocity Relation
of a single muscle fiber by a single stimulus. - Velocity: muscle shortening
- Increasing load = decreasing velocity of muscle
3 stages of contraction: fiber shortening
1. Latent period- a brief interval (1-2ms) of - Decreasing load = increasing velocity
assuming inactivity of the muscle fiber - No load = highest velocity
between the application of stimulus and the - Highest tension = no velocity
application of tension to the muscle;
corresponds to the time of excitation events Frequency-Tension Relation
that occur in the muscle prior to tension - 1 action potential in a muscle fiber lasts only
building. for 0.1-0.2secs
2. Contraction period- steep upward curve - Summation: possible to stimulate the muscle
from the pt. of tension development to the pt. to contract before its first contraction has
of peak tension development of the muscle finished; summated contraction
3. Relaxation period- downward curve; muscle - Unfused tetanus: incomplete summations
resume its original length - Treppe contractions: unfused tetanus in an
ascending manner; bladder-like contractions
3 main kinds of muscle contraction: (german); fundamental reason why we have to
(based on relative magnitudes of load and tension) warm up when we gauge in muscular activity;
● Isometric contraction we make calcium ions more available and at the
- Load > tension same time increase the # of myofibrils
- Muscle develops tension but does not shorten contracting w/ an increasing stimuli.
and move the load or object - Fused tetanus/summation: complete
- Shorter latent period* summation that produces a plateau of the
- Longer duration of mechanical event* contractions; does not go on indefinitely,
● Isotonic contraction produces a downward slope at one point
- Tension > load (muscle fatigue); even in continuous application
- Load or object is moved by the muscle of stimulus, no contraction can be made
- Longer latent period* anymore in the fatigued muscle; fatigued
- Briefer duration of mechanical event or muscle= loss of energy reserves or source
shortening* (ATP)
● Lengthening contraction:
- “eccentric contraction” Length-Tension Relation
- Load is much greater than what the maximum - The strength or tension that can be developed
isometric tension can develop; muscle stretches by a muscle can be changed by the length of
because load > max. isometric tension the fiber before contraction.
- 60% longer or shorter from the optimum
*Reason for this difference: length = no tension when stimulated
- In the isometric twitch, tension begins to - Increase length from this point = active
increase as soon as the first cross-bridge is isometric tension @ each length is increased
up to a maximum optimum length
