Muscle mechanics

Question 1

What are the mechanical properties of muscle & tendon?

Answer 1

Muscle properties: Extensibility, elasticity, irritability, contractility
Tendon properties; Extensibility, elasticity

Question 2

Define elasticity in the context of muscle mechanics.

Answer 2

Elasticity is the ability of muscle and tendon to return to their original shape after being deformed

Question 3

Define irritability (or excitability) in the context of muscle mechanics.

Answer 3

Irritability is the ability of muscle to respond to a stimulus, such as a neuromotor signal. Tendons and membranes do not have this property

Question 4

Define contractility in the context of muscle mechanics.

Answer 4

Contractility is the ability of muscle to generate active voluntary tension in response to an electrical stimulus. Tendons and membranes cannot do this.

Question 5

Define extensibility

Answer 5

The ability of muscle and tendon to elongate under load. Only tendons can do this

Question 6

What is the Musclulotendinous Unit (MTU)

Answer 6

▪ The complex of muscle and tendon that work together to generate force.
▪ Involves muscle fibers, membranes, and tendons connecting muscle to bone.
▪ Components: Contractile component (CC), Parallel elastic component (PEC), Series elastic component (SEC)

Question 7

What are the components of the musculotendinous unit (MTU) and their roles in generating tension?

Answer 7

• Contractile component: Sarcomeres within muscle fibers that generate active tension through voluntary contraction.
• Parallel elastic component: Muscle membranes (endomysium, perimysium, epimysium) that generate passive tension when elongated.
• Series elastic component: Tendons that generate passive tension when elongated.

Question 8

Contractile Component (CC) of MTU

Answer 8

▪ Sarcomere.
▪ Generates active tension
▪ Contains actin and myosin

Question 9

Explain the length-tension relationship of a sarcomere.

Answer 9

Sarcomeres generate optimal force at an optimal length (around two nanometers) due to optimal cross-bridge formation. Force production decreases if the sarcomere is too short or too long.

Question 10

Explain the velocity-force curve of muscle.

Answer 10

As concentric angular velocity increases, force production decreases. Conversely, as concentric angular velocity decreases, force production increases. Eccentrically, muscles can handle far greater loads.

Question 11

Velocity-Force Curve

Answer 11

Describes the relationship between the velocity of muscle contraction and the force it can produce.

• Concentric: Higher velocity, lower force. Slower velocity, higher force.
• Eccentric: Higher force than concentric

Question 12

How does fatigue affect the velocity-force relationship?

Answer 12

As a muscle fatigues, movement slows down, allowing for the generation of more relative force at slower movements.

Question 13

Optimal Sarcomere Length

Answer 13

• Around two nanometers.
• Allows for optimal cross-bridge formation between myosin heads and actin filaments

Question 14

Active Insufficiency

Answer 14

• Reduced ability to generate force when a muscle is in a shortened position.
• Z-lines get too close, preventing further shortening

Question 15

Passive Tension

Answer 15

• Tension generated by non-contractile tissues (membranes, tendons) when stretched.
• Contributes to overall force production, especially at longer muscle lengths.
• Generates quickly

Question 16

How can the stretch-shortening cycle be trained?

Answer 16

It can be trained by increasing the elasticity of tissue through thickening and strengthening and through neuromotor training.

Question 17

Length-Tension Relationship of MTU

Answer 17

• Combination of active and passive tension curves.
• Active tension (sarcomere) resembles an inverted U.
• Passive tension increases with muscle elongation.
• Total tension is the sum of active and passive tension

Question 18

Resting Length

Answer 18

The position where a muscle generates optimal tension voluntarily

Question 19

Eccentric Contractions

Answer 19

• Muscle lengthens under tension.
• Can handle greater loads than concentric contractions (approximately 140% of 1RM).
• Important for training and rehabilitation.

Question 20

What is Power Training

Answer 20

• Involves training at intensities and velocities that maximize power output.
• For active, healthy adults, a good starting point is around one-third of 1RM

Question 21

Moment Arm

Answer 21

• The perpendicular distance between the muscle force vector and the axis of rotation.
• A longer moment arm allows for greater torque generation with the same amount of force

Question 22

Mechanical Advantage

Answer 22

• The ratio of the effort arm (moment arm of the muscle) to the resistance arm.
• A mechanical advantage greater than 1 means the muscle can generate more torque with less force

Question 23

Torque Transfer

Answer 23

Multi-joint muscles can transfer torque from one joint to another.
* Example: Knee extension can contribute to plantar flexion due to the gastrocnemius

Question 24

What is Lombard’s Paradox?

Answer 24

Lombard’s paradox is the observation that antagonistic muscles (like the quads and hamstrings) can contract simultaneously during a movement like a sit-to-stand.

Question 25

How is Lombard's Paradox explained?

Answer 25

Lombard's paradox is explained by considering moment arms and mechanical advantage. Even if antagonistic muscles contract simultaneously, the muscle with the greater moment arm will dominate the movement.

Question 26

What is the role of the muscle spindles in the stretch-shortening cycle?

Answer 26

The muscle spindles, which are proprioceptors of the muscle, are often attributed to some of the stretch-shortening cycle. There is also the passive extensibility and elasticity in muscle, which causes that stretch-shortening cycle.

Question 27

How do you remove the stretch-shortening cycle from a vertical jump test?

Answer 27

You remove the stretch-shortening cycle by having individuals go into their low position and then hold it there for two seconds before they jump vertically.

Question 28

According to Lombard's Paradox, why is the force of the rectus femoris still beneficial at the hip joint?

Answer 28

The force of the rectus femoris is beneficial because it helps to stabilize the hip joint by pulling the pelvis into the femur. These compressive forces hold bones together.

Question 29

How can two-joint muscles transfer torque from one joint to another?

Answer 29

Two-joint muscles like the gastroc can transfer knee extensor torque to a plantar flexor torque. Knee extension could be a fixed femur and a moving tibia or a fixed tibia and a moving femur.

Question 30

How can muscles that aren't voluntarily contracting still cause movement?

Answer 30

Muscles that aren't voluntarily contracting can still generate tension and cause movement.

Question 31

What is the importance of the velocity force curve in relation to the specificity principle?

Answer 31

The velocity force curve is important for the specificity principle, which helps determine when and how to engage muscles to predictably see how they develop or adapt.

Question 32

How does Lombard's Paradox relate to squatting?

Answer 32

Knee extension can contribute to plantar flexion, and the quads can plantar flex the ankle. Furthermore, hip extension is going to also extend the knee. Therefore, a hip-dominant or knee-dominant squat is not possible.

Question 33

What makes estimating moment arms difficult, and what techniques improve accuracy?

Answer 33

Estimating moment arms is difficult because everyone is unique. However, in vivo measurements using MRIs and ultrasounds have improved accuracy.

Question 34

Why is it important to accurately find and estimate relative muscular effort?

Answer 34

Accurately finding and estimating relative muscular effort is important for training purposes.

Question 35

What role do hamstrings play in stabilizing forces?

Answer 35

Hamstrings and other muscles contribute to stabilizing forces by pulling the tibia into the femur, which prevents dislocation during movements like squats.

Question 36

What does it mean to have mechanical advantage?

Answer 36

Mechanical advantage means if you have mechanical advantage, if numerically it is greater than one. It means there is an advantage mechanically. If mechanical advantage is less than one, it means there is a disadvantage.

Question 37

What is the Velocity-Power Curve

Answer 37

Illustrates the relationship between muscle contraction velocity and power output. * Power = Force x Velocity. * Peak power occurs at approximately one-third of peak velocity and one-third of peak force in active, healthy adults

Question 38

Why is it inappropriate to train at levels that are too fast or too heavy, according to the velocity-power curve?

Answer 38

Because you will become more broken.

Question 39

How can eccentric contractions be exploited for training?

Answer 39

You can exploit eccentric strength by stimulating muscles eccentrically, particularly in individuals who have fatigue or weakness. The same muscles that are used to raise resistance are almost always the same muscles used to lower resistance

Question 40

In addition to the force that can be generated at a given velocity of movement, what else is important to consider?

Answer 40

The power that can be generated.