MNB.7 Skeletal Lever System Quiz

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Questions and Answers

Which type of muscle architecture is designed for fine control?

Parallel muscles

Quadriceps muscles

Pennate muscles

Eyelid muscles (correct)

What does the rate of force development primarily measure?

Maximal strength over prolonged contraction

Muscle endurance over time

Explosive strength in initial contraction (correct)

Flexibility during muscle contraction

What type of muscles have a larger physiological cross-sectional area (PCSA) compared to parallel muscles?

Circular muscles

Parallel muscles

Pennate muscles (correct)

Striated muscles

What factor does NOT influence the maximum tension that a muscle can produce?

Color of muscle fibers Signup and view all the answers

Which muscle type is likely to have a reduced range of motion?

Pennate muscles Signup and view all the answers

How do sarcomeres in parallel muscles differ from those in pennate muscles?

Pennate muscles have shorter fiber lengths which increases force production Signup and view all the answers

In the context of muscle force development, which of the following terms refers to the maximum tension a muscle can produce?

Specific tension Signup and view all the answers

What happens to the maximum force generated during muscle contraction in the first 200 milliseconds?

It increases rapidly Signup and view all the answers

Which component does NOT form part of a lever in the skeletal and muscular system?

Elastic band Signup and view all the answers

What is the primary function of levers in the skeletal and muscular systems?

To facilitate movement through the application of force Signup and view all the answers

Why can pennate muscles generate more force compared to parallel fibered muscles?

Pennate fibers are more numerous per cross-sectional area Signup and view all the answers

What is a consequence of maintaining a low center of gravity in a rugby player?

Increased stability Signup and view all the answers

Which statement about muscle length and tension is accurate?

Optimal tension occurs at the relaxed state or normal resting length. Signup and view all the answers

Which statement is true regarding the force development of muscles?

Type of muscle architecture affects the force production capability Signup and view all the answers

What does the angle of muscle fibers (α) influence in muscle force production?

Force development Signup and view all the answers

What is the mass of the torso and head for a body with mass M of 70 kg?

41.5 kg Signup and view all the answers

Which of the following best describes the role of the fulcrum in a lever system?

It is the point around which the lever rotates. Signup and view all the answers

Which segment has the highest mass percentage of the total body mass M?

Torso and Head Signup and view all the answers

What increases the stability of an object according to the principles of center of gravity?

A lower center of gravity Signup and view all the answers

How is stability characterized when the center of gravity is outside the base of support?

Unstable Signup and view all the answers

Which segmented mass is the smallest fraction of the total body mass M?

Forearms and hands Signup and view all the answers

What effect does increasing the area of the base support have on stability?

It typically increases stability Signup and view all the answers

What is the mass of the upper arms for a body with mass M of 70 kg?

3.7 kg Signup and view all the answers

When a rugby player stands with their feet well apart, what aspect of stability are they primarily addressing?

Increased base of support Signup and view all the answers

What is torque primarily dependent on?

The magnitude of the force and the distance from the pivot Signup and view all the answers

What does a lever use to change the direction of a force?

The fulcrum Signup and view all the answers

Which statement accurately describes how torque is calculated?

Torque accounts for the angle of force and distance from the pivot. Signup and view all the answers

In a lever system, the effort is defined as:

The force applied to move the load Signup and view all the answers

What is the direction of the moment if a force causes a clockwise rotation?

Negative Signup and view all the answers

How does the angle of force application affect the torque generated?

The torque is maximized at 90°. Signup and view all the answers

If a force of 445 N acts at an angle of 82°, what must be considered in torque calculation?

The distance and the angle of the force Signup and view all the answers

In applying the equation τ = F sin θ d, what does θ represent?

The angle between the force and the distance from the pivot Signup and view all the answers

What is the formula used to calculate the torque produced by a force?

τ = F sin θ d Signup and view all the answers

If the deltoid muscle exerts a force of 67 N at an angle of 15°, what is the torque generated about the shoulder joint?

3.12 Nm Signup and view all the answers

What condition must be satisfied for an object to be in equilibrium regarding torque?

Net Torque must be zero Signup and view all the answers

When the lower leg rotates clockwise about the knee, what type of torque does the hamstring muscle produce?

Anticlockwise torque Signup and view all the answers

What is the method to find the force generated in the biceps muscle when the arm is holding a weight at equilibrium?

Add clockwise and anticlockwise torques and set equal to the weight Signup and view all the answers

What is the correct equation to calculate the force in the biceps muscle given the angular distances and applied weights about the elbow?

30 * 0.46 + 18 * 0.15 = FB * 0.04 Signup and view all the answers

If the biceps muscle's force is calculated to be 412.5 N, what does this imply about the forces acting on the arm?

The net torque is zero Signup and view all the answers

Which of the following statements is true regarding the static equilibrium of a holding arm?

The clockwise and anticlockwise forces cancel each other out. Signup and view all the answers

What is the correct expression to calculate the force FE based on the provided information?

$FE = 412.5 - 48$ Signup and view all the answers

What does a mechanical advantage (M.A.) greater than 1 indicate?

The lever system is efficient and designed for strength. Signup and view all the answers

In a Class III lever, which of the following is true regarding the relationship of forces?

The applied force is generated in the bicep muscle. Signup and view all the answers

What is a consequence of poor lifting techniques according to the content?

Increased stress on the back muscles. Signup and view all the answers

What characterizes a lever system with a mechanical advantage less than 1?

The system is inefficient and prioritizes speed. Signup and view all the answers

In a healthy person standing upright, which part of the body bears normal load?

Lumbar vertebrae Signup and view all the answers

What force acts downward in the net force equation provided?

Weight of the body and additional forces. Signup and view all the answers

Which scenario is most likely to increase loading on the back muscles?

Lifting heavy objects with poor technique. Signup and view all the answers

Study Notes

Musculoskeletal System, Nervous System & Bioelectricity, MNB.7 Skeletal Lever System

Learning Outcomes: Define Centre of Gravity (CofG), understand its significance in biomechanical calculations, draw a diagram of force development in human muscle and factors affecting maximum tension, define moment, torque & lever, outline conditions for static equilibrium in anatomical examples, demonstrate biomechanical force calculation using moments, define & calculate mechanical advantage, differentiate between Class I, II, and III levers with anatomical examples, and discuss back injury risks associated with poor lifting technique.

Centre of Gravity

Definition: The centre of gravity (CofG) is the point where an object's mass or weight is evenly distributed and through which gravity's force acts.
Uniform Objects: In uniformly dense and symmetrical objects, the CofG is at the geometric center.
Significance: Crucial for understanding and calculating forces in biomechanics and determining stability.
Location in Body: The CofG usually lies at the midpoint of a body segment, like the arm.
Human Body Segments: The body can be divided into segments (e.g., head, torso, arms, legs) with each segment having its own CofG and mass. Values are given for these segments within a human of 70kg mass.

Centre of Gravity and Stability

Stability: An object is stable when its CofG lies above its base of support.
Base of Support: The portion of a body that is in contact with the supporting surface.
Stability & Base Area: Increasing the base area increases stability. Lowering the CofG enhances stability.

Force Development

Rate of Force Development: Measures how quickly a muscle generates force in the initial contraction phase. It's a key factor in explosive strength.
Force and Muscle Contraction: The maximum force generated in muscle contraction is influenced by factors during muscle contraction.
Muscle Architecture Types: Parallel Muscles (fibers run parallel to tendon) and Pennate Muscles (fibers run at an angle to tendon). Pennate muscles generally generate more force.
Physiological Cross-Sectional Area (PCSA): The maximum tension a muscle can produce roughly corresponds to the PCSA at the thickest part in parallel fibers.
Muscle Length: Maximum tension is generally achieved when muscles are at their resting length.

Levers

Lever System: Bones act as levers, muscles as forces and joints as fulcrums to generate motion.
Fulcrum: The fixed point around which a lever pivots.
Load: The object or force being moved or balanced.
Effort: The force applied to overcome the load.
Moment of Force: The turning effect of a force, calculated as the product of the force and its perpendicular distance from the fulcrum (torque).
Torque: Rotational force, causing rotation around an axis.
Calculating Torque: Torque is calculated by multiplying the force by the perpendicular distance from the fulcrum to the line of action of the force (τ= F sinθd) where θ is the angle between the force and the lever arm.

Equilibrium

Static Equilibrium: When the net torque and net force on an object are zero.
Net Torque: Sum of all torques acting on an object.
Net Force: Sum of all forces acting on an object.

Mechanical Advantage (MA)

Definition: The ratio of the load force to the effort (applied) force, indicating the force amplification gained by the lever.
Efficiency: MA greater than 1 means effort needed is less than the load, (efficient). MA less than 1, effort needed is more than the load (inefficient).

Classes of Levers

Class I Levers: Fulcrum is in the middle between the load and effort. Examples include neck muscles acting on the head, which often provide speed of movement but are not always the most efficient.
Class II Levers: Load is in the middle between the fulcrum and effort. Examples include calf muscles acting when lifting a load off the floor, often efficient for strength.
Class III Levers: Effort is in the middle between the fulcrum and load. Examples include the biceps muscle used in flexing the elbow—often more efficient for speed and range of motion but less efficient for increased force.

Back Injury

Normal Load: Consistent stress across the lumbar vertebrae.
Increased Load: Depending on the type of activity, the loading on the back can vary significantly.
Lifting Technique: Improper technique can substantially increase stress on the back muscles and increase risk for injury.
Safe Lifting Techniques: Proper lifting techniques, including bending from the knees and using the legs/core muscles, reduce back injury risk by lowering the forces that muscles must generate.

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Description

Test your knowledge on the Skeletal Lever System, Centre of Gravity, and biomechanics. This quiz covers definitions, calculations, and anatomical examples related to leverage, moment, and torque. Understand how these concepts impact human movement and injury risk.