5) Force and Speed of mm contraction Flashcards
Force and Speed of MM contraction
What are four factors that impact the Force and Speed of MM contraction?
1) Type and number of motor units recruited/activated
2) Length-tension relationship (Sarcomere length)
3) Frequency of stimulation of the motor units (Rate coding)
4) Force-Velocity relationship
i) Type and number of motor units recruited/activated
* ↑ number of motor units → ↑ force
* ↑ type II fibers → ↑ force and velocity
- Type II motor units generate more force: (larger fibres // fast myosin ATPase // More developed SR) → ↑ speed of cross-bridge cycling
- Larger MM have more muscle fibers and generate more force
- Amount of Force Generated can be graded to meet demands of the task (ie number of Motor Units recruited depends on task)
ii) Length-tension relationship (Sarcomere length)
As Muscle length increases:
- passive tension increases (recoil tension/force - No ATP involved) and
- Active tension (tension/force when mm stimulated to contract - Involves ATP // due to cross-bridge cycling) decreases
- Total tension = summation of passive and active tension
iii) Frequency of stimulation of the motor units (Rate coding)
- Single motor unit varies in the level of force generated depending on frequency of stimulation
- Twitch = smallest contractile response of a MM fiber or motor unit to a single electrical stimulus
- Summation = Less relaxation time between APs
- Tetanus = No relaxation time between APs
iv) Force-Velocity relationship
- Concentric contractions (shortening): Increase speed → Decrease Force
- Eccentric contractions (Lengthening): Increase speed → Increase Force because of Passive Tension
How does the Type and number of motor units recruited/activated impact the Force and Speed of MM contraction?
i) Type and number of motor units recruited/activated
↑ number of motor units → ↑ force
↑ type II fibers → ↑ force and velocity
- Type II motor units generate more force: (larger fibres // fast myosin ATPase // More developed SR) → ↑ speed of cross-bridge cycling
Larger MM have more muscle fibers and generate more force
Amount of Force Generated can be graded to meet demands of the task (ie number of Motor Units recruited depends on task)
i) Type and number of motor units recruited/activated
* ↑ number of motor units → ↑ force
* ↑ type II fibers → ↑ force and velocity
- Type II motor units generate more force: (larger fibres // fast myosin ATPase // More developed SR) → ↑ speed of cross-bridge cycling
- Larger MM have more muscle fibers and generate more force
- Amount of Force Generated can be graded to meet demands of the task (ie number of Motor Units recruited depends on task)
ii) Length-tension relationship (Sarcomere length)
As Muscle length increases:
- passive tension increases (recoil tension/force - No ATP involved) and
- Active tension (tension/force when mm stimulated to contract - Involves ATP // due to cross-bridge cycling) decreases
- Total tension = summation of passive and active tension
iii) Frequency of stimulation of the motor units (Rate coding)
- Single motor unit varies in the level of force generated depending on frequency of stimulation
- Twitch = smallest contractile response of a MM fiber or motor unit to a single electrical stimulus
- Summation = Less relaxation time between APs
- Tetanus = No relaxation time between APs
iv) Force-Velocity relationship
- Concentric contractions (shortening): Increase speed → Decrease Force
- Eccentric contractions (Lengthening): Increase speed → Increase Force because of Passive Tension
What is the Length-Tension relationship and how does it relate to Force/Speed of MM contraction?
As Muscle length increases:
- ? tension increases (recoil tension/force - No ATP involved) and
- ? tension decreases (tension/force when mm stimulated to contract - Involves ATP // due to cross-bridge cycling)
- Total tension = ?
Length-tension relationship (Sarcomere length)
As Muscle length increases:
- passive tension increases (recoil tension/force - No ATP involved) and
- Active tension (tension/force when mm stimulated to contract - Involves ATP // due to cross-bridge cycling) decreases
- Total tension = summation of passive and active tension
i) Type and number of motor units recruited/activated
* ↑ number of motor units → ↑ force
* ↑ type II fibers → ↑ force and velocity
- Type II motor units generate more force: (larger fibres // fast myosin ATPase // More developed SR) → ↑ speed of cross-bridge cycling
- Larger MM have more muscle fibers and generate more force
- Amount of Force Generated can be graded to meet demands of the task (ie number of Motor Units recruited depends on task)
ii) Length-tension relationship (Sarcomere length)
As Muscle length increases:
- passive tension increases (recoil tension/force - No ATP involved) and
- Active tension (tension/force when mm stimulated to contract - Involves ATP // due to cross-bridge cycling) decreases
- Total tension = summation of passive and active tension
iii) Frequency of stimulation of the motor units (Rate coding)
- Single motor unit varies in the level of force generated depending on frequency of stimulation
- Twitch = smallest contractile response of a MM fiber or motor unit to a single electrical stimulus
- Summation = Less relaxation time between APs
- Tetanus = No relaxation time between APs
iv) Force-Velocity relationship
- Concentric contractions (shortening): Increase speed → Decrease Force
- Eccentric contractions (Lengthening): Increase speed → Increase Force because of Passive Tension
Length-tension relationship
What is Passive Tension?
Recoil tension/force
- Doesn’t require energy (No ATP involved)
- Tension generated by “spring-like” components of MM (titin, tendons, Connective Tissue)
- “Stretching a rubber band”
What is the “Equilibrium Length” of MM?
- Length of relaxed MM just before stretching
- Resting Length: Length of MM when it creates Maximal force
- Length of MM were it detached from bone
- Increase length of MM = Increase Sarcomere length
What is the length of muscle when it creates the maximum force?
Resting length
- Length when Maximum number of Cross-bridges is formed
Why is Max force observed in Resting Length MM and NOT when muscle is at MAX length?
The Maximum number of Crossbridges that can form is observed during Resting length
- Best alignment of Myosin and Actin
- ie Most overlap of Actin-myosin and greatest cross-bridge cycling
- as muscle stretches past this point, lose alignment
Force depends on the number of heads of actin and myosin that overlap
Each head that overlaps produces 1 unit of force therefore, more cross-bridges = more force
What is Total Tension?
- The summation of passive and active tension
- Total = Active up until Equilibrium length is reached
- After equilibrium Length: Total Tension = Passive + Active)
How does flexibility play into Force of MM contraction?
Max MM Length?
Comparison at same MM length to less flexible person?
- The more flexible a person is, the longer the muscle can be stretched
- The longer the muscle length, the greater the total force/Tension (Increase Passive Tension)
- ie the more a mm is stretched, the more potential energy is stored = Increase Passive tension
At the Same Muscle Length:
- More flexible person generates LESS tension (less RECOIL) than someone who is less flexible at the same length
- Increased Flexibility = Increased room to stretch = Increased possible Passive Tension
- Less flexible MM reach Maximum length sooner
What is Active Insufficiency (using bicep curl example)
1 in image:
- Muscle is fully contracted (active) = Short sarcomere
- Some actins are blocking each other - limits Myosin-actin overlap = limits cross-bridge cycling
- Low force production - weak
What is Passive Insufficiency? (use bicep curl example)
When muscle is fully extended:
- Minimal Actin-myosin overlap
- Low force production - weak
What is Rate coding?
Frequency of stimulation (action potentials)
Frequency of stimulation of the motor units (?)
- Single ? varies in the level of ? generated depending on frequency of stimulation
- ? = smallest contractile response of a MM fiber or motor unit to a single electrical stimulus
- ? = Less relaxation time between APs
- ? = No relaxation time between APs
Frequency of stimulation of the motor units (Rate coding)
- Single motor unit varies in the level of force generated depending on frequency of stimulation
- Twitch = smallest contractile response of a MM fiber or motor unit to a single electrical stimulus
- Summation = Less relaxation time between APs
- Tetanus = No relaxation time between APs
i) Type and number of motor units recruited/activated
* ↑ number of motor units → ↑ force
* ↑ type II fibers → ↑ force and velocity
- Type II motor units generate more force: (larger fibres // fast myosin ATPase // More developed SR) → ↑ speed of cross-bridge cycling
- Larger MM have more muscle fibers and generate more force
- Amount of Force Generated can be graded to meet demands of the task (ie number of Motor Units recruited depends on task)
ii) Length-tension relationship (Sarcomere length)
As Muscle length increases:
- passive tension increases (recoil tension/force - No ATP involved) and
- Active tension (tension/force when mm stimulated to contract - Involves ATP // due to cross-bridge cycling) decreases
- Total tension = summation of passive and active tension
iii) Frequency of stimulation of the motor units (Rate coding)
- Single motor unit varies in the level of force generated depending on frequency of stimulation
- Twitch = smallest contractile response of a MM fiber or motor unit to a single electrical stimulus
- Summation = Less relaxation time between APs
- Tetanus = No relaxation time between APs
iv) Force-Velocity relationship
- Concentric contractions (shortening): Increase speed → Decrease Force
- Eccentric contractions (Lengthening): Increase speed → Increase Force because of Passive Tension
Define Summation:
Multiple stimuli occurring quickly enough that the muscle cannot fully relax between stimuli and the force from one twitch is added to the force from the previous twitch
- Produces stronger muscle contraction
What is Tetanus?
Multiple stimuli occurring at such a rate that frequency of muscle contraction is such that the maximal tension is generated without any relaxation of the muscle
- Results in smooth, sustained contraction
Force and Speed of MM contraction
? contractions: Maximal force decreases progressively at higher speeds
- ↑Speed → ↓Force
- Requires more, synchronous cross-bridge cycling
? contractions: Fast contractions allow maximal application of force
- ie Increasing speed leads to increased force because Passive tension is involved
- Still can’t recruit enough motor units but Force increases nonetheless due to passive tension
Force and Speed of MM contraction
Concentric (shortening) contractions: Maximal force decreases progressively at higher speeds
- ↑Speed → ↓Force
- Requires more, synchronous cross-bridge cycling
Eccentric (lengthening) contractions: Fast contractions allow maximal application of force
- ie Increasing speed leads to increased force because Passive tension is involved
- Still can’t recruit enough motor units but Force increases nonetheless due to passive tension
Force and Speed of MM contraction
Concentric (shortening) contractions:
- Maximal force ? as speed ?
- (?Speed → ?Force)
- Requires more ?
Eccentric (lengthening) contractions:
- Maximal force ? as speed?
- ?Speed → ?Force
- because ? is involved
Force and Speed of MM contraction
Concentric (shortening) contractions: Maximal force decreases progressively at higher speeds
- ↑Speed → ↓Force
- Requires more, synchronous cross-bridge cycling
Eccentric (lengthening) contractions: Fast contractions allow maximal application of force
- ↑Speed → ↑Force
- because Passive tension is involved
- Still can’t recruit enough motor units but Force increases nonetheless due to passive tension
