Muscle mechanics Flashcards
What are the mechanical properties of muscle?
Define elasticity in the context of muscle mechanics.
Elasticity is the ability of muscle and tendon to return to their original shape after being deformed
Define irritability (or excitability) in the context of muscle mechanics.
Irritability is the ability of muscle to respond to a stimulus, such as a neuromotor signal. Tendons and membranes do not have this property
Define contractility in the context of muscle mechanics.
Contractility is the ability of muscle to generate active voluntary tension in response to an electrical stimulus. Tendons and membranes cannot do this.
What are the components of the musculotendinous unit (MTU) and their roles in generating tension?
- 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.
Explain the length-tension relationship of a sarcomere.
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.
Explain the velocity-force curve of muscle.
As concentric angular velocity increases, force production decreases. Conversely, as concentric angular velocity decreases, force production increases. Eccentrically, muscles can handle far greater loads.
How does fatigue affect the velocity-force relationship?
As a muscle fatigues, movement slows down, allowing for the generation of more relative force at slower movements.
How can the stretch-shortening cycle be trained?
It can be trained by increasing the elasticity of tissue through thickening and strengthening and through neuromotor training.
What is Lombard’s Paradox?
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.
How is Lombard’s Paradox explained?
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.
What is the role of the muscle spindles in the stretch-shortening cycle?
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.
How do you remove the stretch-shortening cycle from a vertical jump test?
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.
According to Lombard’s Paradox, why is the force of the rectus femoris still beneficial at the hip joint?
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.
How can two-joint muscles transfer torque from one joint to another?
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.
How can muscles that aren’t voluntarily contracting still cause movement?
Muscles that aren’t voluntarily contracting can still generate tension and cause movement.
What is the importance of the velocity force curve in relation to the specificity principle?
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.
How does Lombard’s Paradox relate to squatting?
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.
What makes estimating moment arms difficult, and what techniques improve accuracy?
Estimating moment arms is difficult because everyone is unique. However, in vivo measurements using MRIs and ultrasounds have improved accuracy.
Why is it important to accurately find and estimate relative muscular effort?
Accurately finding and estimating relative muscular effort is important for training purposes.
What role do hamstrings play in stabilizing forces?
Hamstrings and other muscles contribute to stabilizing forces by pulling the tibia into the femur, which prevents dislocation during movements like squats.
What does it mean to have mechanical advantage?
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.
Why is it inappropriate to train at levels that are too fast or too heavy, according to the velocity-power curve?
Because you will become more broken.
How can eccentric contractions be exploited for training?
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
In addition to the force that can be generated at a given velocity of movement, what else is important to consider?
The power that can be generated.
