Chapter 6: The Biomechanics of Skeletal Muscle

What is an example of active insufficiency?

The finger flexors cannot generate maximum grip force when they are shortened during an accompanying wrist flexion

What is a characteristic of fast-twitch oxidative glycolytic fibers?

Fatigue rate is intermediate (faster than type I but slower than type IIB).

What is a motor unit?

a single motor neuron and all muscle fibers it innervates

What are potential disadvantages of multijoint muscles?

active insufficiency passive insufficiency

A muscle directly involved in causing a segment to move is called what (i.e. prime mover)?

agonist

During the down phase of a knee extension exercise, what role does the hamstring group play?

antagonist

During the kicking and follow-through phases of a punt, the quads are experiencing what type of contraction?

concentric

What are the four behavioral properties of muscle tissue?

contractility extensibility elasticity excitability or irritability

What statement represents the force-velocity relationship for muscle tissue?

contraction is slower when the load is heavier

What type of muscle contraction is employed by the elbow flexors when slowly lowering your backpack to your desk?

eccentric

What type of strength training is particularly associated with subsequent muscular soreness?

eccentric

What types of muscle tension is commonly used as a braking mechanism to slow limb movement?

eccentric

When an opposing torque at a joint is greater than the torque created by a muscle, what type of contraction occurs in that muscle?

eccentric

A single muscle cell is called what?

fiber

Which behavioral property of muscle tissue is defined as "the ability to respond to a stimulus"? Hint: Just the ability - not the response of that ability.

irritability

A contraction in which there is not a change in length is called what?

isometric

A muscle contraction which does not result in a change in length is called

isometric

Origin attachment is closet to the ____

middle of the body

In human skeletal muscle, force generation capability is highest in which of the following conditions?

muscle is slightly lengthened under tension

What term best describes the rate of torque production at a joint? Think work/time.

muscular power

The amount of torque a muscle group can generate at a joint is used to measure what?

muscular strength

When flexing the elbow, the biceps brachii, brachioradialis, and brachialis are the three major agonists recruited to perform this movement (all perform flexion at the elbow). However, the biceps brachii also causes supination, an undesired movement. Therefore another muscle acting as a ________, causing ________ must be recruited to prevent the undesired motion.

neutralizer; pronation

The _____________ fiber arrangement is a pattern of fibers within a muscle with short fibers attaching to one or more tendons.

pennate

What are characteristics of muscle fatigue?

reduction in muscle force reduction in shortening velocity prolonged relaxation of motor units between recruitment

What are the characteristics of a pennate muscle?

relatively strong relatively low range of motion

A ______________ muscle fiber reaches peak tension relatively slowly.

slow-twitch

The component force which is parallel to the moving bone and acts to pull the bones together at the joint is called what?

stabilizing force

In what activities do the biceps brachii function as antagonists?

straightening the elbow during a push-up

A pattern of eccentric contraction followed immediately by concentric contraction is called ________________ cycle.

stretch-shortening

The A.V. Hill model has three components that act together to describe the behavior of whole muscle. Where is the series elastic component (SEC) of a muscle found?

tendon

During the execution of a pull-up when the chin is over the bar, which force exerted by the biceps brachii is greatest at the elbow?

the dislocating force

The attachment that is distal is ____

the insertion

The muscle's origin is usually broader than ____

the insertion

The muscle's insertion is usually narrower than ____

the origin

What time periods is termed electromechanical delay? In motor control research, this may be referred as, "motor reaction time".

the time required for the muscle to initiate the development of tension after receipt of the nerve impulse

The torque of a muscle (rotary component) is greatest in what position?

when the muscle insertion is 90° to the bone

Which of the following is true regarding the parallel elastic component (PEC) of muscular elasticity?

This component is provided by the muscle membranes. This component provides resistance when a muscle is passively stretched.

What is true regarding the stretch-shortening cycle (SSC)?

When a muscle is stretched just prior to contraction, the resulting contraction is more forceful. An eccentric contraction is followed by a concentric contraction. The SSC promotes storage of elastic energy.

Which type of muscle could serve as an antagonist of a flexor?

extensor

During the first 12 weeks of resistance training, strength gains are classically attributed to what?

improved innervation of the muscle

Muscle hypertrophy in humans is primarily due to what?

increase in size of muscle fibers

The elasticity of human skeletal muscle tissue is believed to be due primarily to which of the following?

the series elastic component

What likely contributes to the stretch-shortening cycle?

the series elastic component muscle spindle activity

Muscle fibers are typically recruited according to what?

the size principle (the smaller motor units first)

In concentric muscle action, velocity increases at the expense of what?

a decrease in force and vice versa As the velocity of a muscle shortening cycle increases, the cycling rate of the cross bridges increases, leaving fewer cross-bridges attached at one time.

Explain at least four roles assumed by muscles.

1. A muscle assumes the role of an agonist when it causes a movement. For example, during elbow extension, the triceps are the agonists. 2. A muscle assumes the role of an antagonist when it acts to slow or stop a movement. For example, during the elbow extension, the brachialis and the biceps brachii are the antagonists. 3. A muscle assumes the role of a stabilizer when it acts to stabilize a body part against some other force. For example, during the forearm curl, the wrist flexors and wrist extensors stabilize the wrist. 4. A muscle assumes the role of a neutralizer when it acts to eliminate an unwanted action produced by an agonist. For example, in elbow flexion of a bicep curl, the brachii creates tension which leads to flexion at the elbow and supination of the forearm. If only flexion is desired, then the pronator teres act as a neutralizer to prevent the supination.

List and explain the behavioral characteristics of the musculotendinous unit, including similarities and differences to other tissue.

1. Extensibility is the ability to be stretched or to increase in length. 2. Elasticity is the ability is to return to normal length after a stretch. This elasticity allows a muscle to return to normal resting length after a stretch as well as allowing a smooth transition of tension from muscle to bone. The elasticity of muscle has two major components: the parallel elastic component (PEC) and the series elastic component (SEC). 3. Irritability is the ability to respond to a stimulus. This stimulus is either electrochemical or mechanical. Muscle responds to this stimulus by developing tension. 4. Ability to develop tension is unique to muscle tissue. Tension can either be the shortening or lengthening of muscle length.

List and describe four common muscle injuries.

1. Muscle strains result from the overstretching of muscle tissue. This usually can happen due to overloading of the muscle. Strains vary from being mild, moderate, and severe. Respectively these range from minimal structural damage to a partial tear in muscle tissue to severe tearing of the muscle that can result in functional loss and hemorrhaging. 2. Contusions, sometimes known as muscle bruises, are caused by compressive forces sustained during impacts. In this type of injury, hematomas are within the muscle tissue. 3. Delayed-onset muscle soreness occurs 24-72 after long or strenuous activity. Feelings of pain, swelling, and histological changes that accompany acute inflammation are characteristics of this injury. Microtearing of the muscle tissue is involved. 4. Compartment syndrome is when a hemorrhage or edema within a muscle compartment results from injury or muscular exertion. In this compartment, there is increased pressure and severe damage to the neural and vascular structures. Symptoms are discoloration, loss of sensation, and loss of motor function.

Explain muscular strength. How is it measured? How does it change at different points during range of motion?

Muscular strength is a measurement of the maximum torque generated by an entire muscle group at a joint. It is measured as a collective force-generating capability of a given functional muscle group. The rotary component is maximum in size when it's positioned at 90 degrees to the bone. Here, the muscle is perpendicular to the bone, with change in either direction progressively diminishing it. In the parallel component, in which the the force acts parallel to the attach bone, there is no torque produced. This is because it is directed through the joint center which means that there is a torque of zero. For this reason, the function of this component is to supply a stabilizing component (directed toward the joint center) or a dislocating component (directed away from the joint center).

What do pennate muscles hold over parallel muscles and vise versa?

Pennate muscles are capable of producing more tension per unit of cross-sectional area than parallel muscles. Parallel muscles are capable of producing more range of motion than pennate muscles.

_______________ is a role played by a muscle to stabilize a body part against some other force.

Stabilizer