Biomechanics Exam 1

If the biceps brachii, attaching to the radius 2.5 cm from the elbow joint at an angle of 60°, is exerting a tension of 200N in the muscle, and the triceps brachii, attaching to the radius 3cm away from the elbow joint also at an angle of 60°, exerts a force of 150N of tension in the muscle, how much net torque is present at the joint, in the unit of Nm?

0.43 Nm

If the biceps muscle force F = 25N, the muscle attaches to the radius bone at 4cm from the elbow joint, and the attachment angle θ = 30∘, compute the torque exerted by the muscle (in Nm).

0.5 Nm

Put the following types of synovial joints in order from the least mobile to the most mobile.

1 - Gliding joints 2 - Pivot joints 3 - Saddle joints 4 - Ball-and-socket joints

Order the following muscle structure from the smallest to the largest.

1 - Sarcomere 2 - Myofibril 3 - Muscle fiber 4 - Fascicle 5 - Muscle 6 - Muscle group

The curves above represents the relationship between tensile stress (σ) and tensile strain (ε) for four different biological materials. The "dot" on each curve indicates the yield point/elastic limit and the "x" represents the rupture point. Fill in the blank spaces below with the correct number referring to a material (numbers are listed above corresponding material). You CAN use the same number more than once. The most ductile material is ___. The most brittle material is ___. The strongest material is ___. The toughest material is ___. The stiffest material is ___.

1, 4, 1, 1, 1

If a person holds a 100 N weight in their hand 0.4 m from the elbow, what is the elbow flexor muscle force? Assuming the forearm weight is 11N, forearm center of mass is 0.16m from the elbow joint, biceps brachii muscle attachment site is 0.03m from the elbow joint, and attachment angle is 60

1,607.35 N

A muscle was estimated to have a force producing capacity of 80N per square centimeter (k=80Ncm2). To produce a desired tendon force of 110N, what must be the effective minimum PCSA of the muscle (in cm2)?

1.59 cm^2

The forearm has ___ degrees of freedom, which is made possible by how many joints ____

2, 2

Mark McGwire's last homerun left the bat with a speed of 50m/s at an angle of 35°. What is the vertical component of the initial velocity?

25.0 m/s

The hip joint is one of the most stable joints in the human body. How many degrees of freedom does the hip joint have?

3

Compute the elastic modulus of the specimen. F = 250 N 0.02 m (deltaL) 1 m (L) Cross-sectional area, A = 4 m^2

3,125

If the biceps brachii, attaching to the radius 2.5 cm from the elbow joint at an angle of 60°, is exerting a tension of 200N in the muscle, and the triceps brachii, attaching to the radius 3cm away from the elbow joint also at an angle of 60°, exerts a force of 150N of tension in the muscle, how much extension torque is present at the joint, in the unit of Nm?

3.89 Nm

If the biceps brachii, attaching to the radius 2.5 cm from the elbow joint at an angle of 60°, is exerting a tension of 200N in the muscle, and the triceps brachii, attaching to the radius 3cm away from the elbow joint also at an angle of 60°, exerts a force of 150N of tension in the muscle, how much flexion torque is present at the joint, in the unit of Nm?

4.33 Nm

Mark McGwire's last homerun left the bat with a speed of 50m/s at an angle of 35°. What is the horizontal component of the initial velocity?

43.3 m/s

Compute the torque the shoulder must exert (in Nm) when forearm is flexed (shown in posture B). Upper arm weight = 20 N Forearm/hand weight = 15 N posture B = 15 cm posture A = 30 cm

5.26 Nm

Compute the torque the shoulder must exert (in Nm) when forearm is extended (shown in posture A). Upper arm weight = 20 N Forearm/hand weight = 15 N posture B = 15 cm posture A = 30 cm

7.5 Nm

If the fibers of a pennate muscle are oriented at a 45° angle to a central tendon, how much tension is produced in the tendon when the muscle fiber contract with 110N of force?

77.8

If the fibers of a pennate muscle are oriented at a 30° angle to a central tendon, how much tension is produced in the tendon when the muscle fiber contract with 110N of force?

95.3

This figure shows the stress-strain curves obtained from cortical bone specimens. What mechanical property of the bone this figure highlights?

Ansiotropy

Which exercise exerts more tension at the knee?

Back squat

In the following picture, three lifting strategies were used. Which one exerts the largest amount of tension at the hip and the lumbar spine?

C

Three motor units are shown in the figure below. Identify the large fast-fatigable motor unit(s).

C

Which component of bone contributes most to its elasticity?

Calcium Phosphate. Inorganic component is the major contributor to the elastic property of the bone. Organic materials mainly contribute to the viscoelastic property.

Your friend Sarah was trying to strengthen her quadriceps in an strengthening exercise. She would like to produce the maximum amount of load with the same weight block. Should she place the weight block close to her knee or her ankle?

Close to the ankle

Which of the following lifestyle choices may reduce the risk of osteoarthritis?

Combine strength training exercises with weight-bearing and balance exercises.

When in ascending stairs your quadriceps contract and the leg straightens. This type of contraction is called

Concentric contraction

Which of the following statements best describes the stretch-shortening cycle?

Concentric muscle action is preceded by an eccentric muscle action.

The knee joint has two degrees of freedom and is a ____ joint.

Condyloid

If a stroke occurs in the left side of the brain, the right side of the body will be affected, producing hemiparesis/hemiplegia on the right side of the body. The affected side of the body is the ______ side.

Contralesional

Which descending pathway contains monosynaptic projections? (select all that apply)

Cotocomotorneuronal pathway Corticospinal tract Pyramidal tracts

Given an acceleration of -6 m/s2, which of the following statements is always true? A)Forward motion is occurring. B)Backward motion is occurring. C)Rate of change of position is constant. D)None of the statements are necessarily true.

D) None of the statements are necessarily true.

Osteoarthritis is a leading cause of disability in people 65 and older. It is caused by

Degeneration in articular cartilage

Which one is an example of a kinetic study? A. Measuring push-off force of sprinters when they take off from the starting blocks B. Calculating the acceleration when sprinters take off from the starting blocks C. Calculating the drag force experienced by the runners when they take off from the starting blocks D. A, B & C E. A & C

E. A & C

A motor unit consists of a group of muscles that are innervated by the same motor neuron.

False

Because stretch reflexes are mediated by the monosynaptic spinal pathway and are primitive and stereotypical, they resist modifications by other systems.

False

Muscle spindles are the primary sensory receptors for the musculoskeletal system that alert the CNS of joint position, muscle length, and muscle tension.

False

The horizontal velocity of a shot put is slowed down by gravity 9.81 m/s every second it is in the air.

False

Which reflex causes you to jerk your limb back from a painful stimulus?

Flexor reflex

Match the following brain areas with the major motor disorders

Hemiparesis - Primary motor cortex Ataxia - Cerebellum Parkinson's Disease - Basal ganglia Apraxia - Parietal Cortex

______ describes a condition featuring muscle weakness and impaired control of contralateral limbs resulting from damage to the ______; ______ describes a condition involving the loss of skilled movements that is not due to muscle weakness and is caused by damage to ______.

Hemiparesis, motor cortex; Apraxia, premotor-parietal cortex

Which joint is typically the most stable?

Hip

Following the size principle, in what order are motor units recruited?

I, IIa, IIb

Which one of the following statements about the corticospinal tract is false? It passes through brainstem It contains both direct and indirect pathways It facilitates flexors and suppresses extensors ipsilaterally It supports dexterous control

It facilitates flexors and suppresses extensors ipsilaterally

The examination of projectile characteristics of a high jumper is an example of which type of analysis?

Kinematic

Which of the following is NOT a factor that contributes to EMG signals?

Length of connective tissue in the muscles

When Sarah moved the weight block from knee flexion to extension, did she need to exert more or less force?

More force

In the three-component Hill Model of muscle, which component most closely corresponds to the tissues surrounding the sacromere?

Parallel elastic component

The region between Y and R is called

Plastic region

Which descending pathway originates from the brainstem?

Reticulospinal tract

In the three-component model of muscle, which component most closely corresponds to the tendon?

Series elastic component

Which joint is typically the most flexible?

Shoulder

Reflexive movement is mainly mediated by

Spinal cord

Above images are from different stages of clean and jerk weightlifting. If you were to analyze a short time-window (~0.1 s) around when the photo was taken, which stages would qualify for static analyses? (Select all that apply.)

Stage C & Stage D

In the force-length curve, the total isometric force produced by the muscle at a given length is equal to

Sum of active and passive tension

Shin splints occur when the tibialis anterior pulls on its attachment site on the tibia and on the interosseous membrane between the tibia and the fibula. What kind of loading is this?

Tensile

Describe three types of muscle contractions during a free-weight exercise.

The concentric contraction causes muscles to shorten. An example of this would be the bicep curl. The eccentric contraction causes muscles to lengthen/elongate. An example of this would be the downward motion of squatting. The isometric contraction generates force without changing the length of the muscle. An example of this would be holding a plank until fatigue.

Describe what are the factors that make the hip a stable joint.

The hip joint is connected to numerous muscles and ligaments. These muscles and ligaments provide support, stability and control for the hip joint. It is the muscles and ligaments surrounding the hip that give it its stability.

During the end of a 100-m race, a runner's acceleration is negative. Which statement accurately interprets this observation?

The runner is slowing down while moving in the positive direction

Describe how stress-strain function is computed and the major components of its curve.

The stress-strain curve shows us that the ability of a structure to resist deformation depends on its material composition and organization. The two components of the curve are stress and strain. Stress is computed as force applied over unit area of the force applied. Strain is computed as the change in deformation over the initial length. In order to compute stress-strain as a whole, you simply divide stress by strain. This would be computed as (force/area applied)/(change in deformation). There are many major components of the curve. This includes things like the toe region, where the crimps in the collagen fibers of the tendon are straightening. The yield point is where the object will no longer be able to return to its original shape. The elastic region is where there is the most movement, but there is no permanent deformation. The plastic region is where deformation occurs but there are no tears or ruptures. Lastly, the failure point is when the tissue can no longer support the load.

Describe what are the factors that make the shoulder a flexible joint.

There are many factors that make the shoulder a flexible joint. It is a ball-and-socket joint. It is triaxial, meaning it has three degrees of freedom, rotation in all planes and movement in all directions. This is what makes the shoulder a flexible joint.

Which of the following is NOT true for flexor reflexes? They evoke crossed extensor reflex in the contralateral limb They involve the quick withdrawn response upon noxious stimulus They excite flexors and inhibit extensors in the stimulated limb They are mediated by the monosynaptic spinal pathway

They are mediated by the monosynaptic spinal pathway

Which of the following are the properties of slow twitch fibers (from practice exam 1)

They are smaller in diameter they contract slowly to maximum force they exhibit a shorter electromechanical delay

Which of the following is NOT a property of short-latency stretch reflexes They can be modified by extensive training. They counteract a mechanical disturbance to return the body to its initial position. They can integrate a wide range of arbitrary cortical level input. They are mediated by the mononsynaptic reflex pathway.

They can integrate a wide range of arbitrary cortical level input

Which of the following are the properties of fast twitch fibers (from muscular system quiz)

They exhibit a shorter electromechanical delay than slow twitch fibers. They fatigue quickly. They are smaller in diameter than slow twitch fibers.

Apraxia typically results from lesions that damage secondary motor areas while sparing primary motor cortex.

True

EMG activation is higher when the same force is generated using concentric contraction compared to eccentric contraction.

True

Hemiplesia can be a result from both primary motor cortex and corticospinal tract.

True

When stimulated by an action potential at rest, the same muscle always produces the same amount of tension regardless of other factors such as joint position and angle.

True

Section 'C' of the myogram indicates which physiological process?

Unfused tetanus

The above figure shows the stress-strain curve for a biological material. The stress-strain curves are different for different loading rates. What is this property of a material called?

Viscoelasticity

The _____ motor neurons activate the ______ fibers to produce the force required for the action, and the _____ motor neurons activate the ______ fibers to set the desired level of feedback from the muscle spindles.

alpha, skeletal muscle, gamma, intrafusal

What type of loading force is typically responsible for ski boot fracture?

bending

In the stress-strain curves of different kinds of body tissues (shown below), ligament is more _____ compared to cortical bone.

compliant

The passive tension produced when a muscle is stretched beyond its resting length is mainly due to

connective tissues such as endomysium, epimysium and perimysium

When the alpha motoneurons activate the muscle, for the muscle to continue its contraction, gamma motoneurons are simultaneously to ______, which maintains stretch of the muscle spindles at the same rate as the whole muscle. This ensures that the muscle spindles continue to send information to the brain about muscle position and ________, and recruit more motoneurons.

contract the intrafusal fibers, length

The "new M1" originates ____ pathway.

corticomotoneuronal

Neurons in M1 exhibit ______ at the single neuron level; whereas ______ is determined by _____ at the population level.

direction tuning, a net direction, population vector

At 75% of muscle activation, which of the following produce the highest level of force?

eccentric contraction using the dumbell

During an isotonic contraction, movement has _____ resistance, ______ speed.

fixed, variable

In the question above, given the computed net torque, what motion would the forearm undergo?

flexion

Muscles with lots of sarcomeres in parallel can achieve high

force

During two-legged hopping, the feet contact the ground at touchdown and then leave the ground at toe-off. During the touchdown phase, the quadricepts and triceps surae muscles ____ and velocities of these muscles are ____.

lengthen, negative

Compared with a pennate muscle of the same volume, a fusiform muscle will have

more sarcomeres in series

Analysis of EMG signals in the frequency domain can provide information on:

muscle fatigue during isometric contraction

When muscle spindles are taut

muscles will be more responsive to stretch

A flexor reflex results from

pain such as heat

The following figure shows five typical types of muscle architecture. Type C-E are called ______ fibers, and they typically have more sarcomeres arranged in _____.

penniform, parallel

Muscles with lots of sarcomeres in series can achieve high

range of motion

Which plane of movement is a free throw performed in?

sagittal

In isometric contraction, muscle can produce the greatest force when the length is

slightly longer than resting length

Short-latency stretch reflexes are mediated via _ pathways and mainly regulate _ muscles; long-latency stretch reflexes are mediated via __ pathways and mainly regulate _ muscles.

spinal, proximal; cortical, distal

The point U represent

strength

EMG is NOT a good tool for measuring ______.

the amount of load lifted in pounds

Which of the following is an example of angular motion

the arm of a golfer during a golf-swing

If recording from the motor cortex, the population vector for a single movement would be calculated as

the summed activity of a set of directionally tuned cells in motor regions of the brain.

If recording from the motor cortex, the population vector for a single movement would be calculated as

the summed activity of neurons that have preferred directions in all possible directions.

In the stress-strain curve for tendon shown in the Achilles Tendon video, the uncrimping of fibers is the ____ region of a typical stress-strain curve, and the 8% strain point is typically called ____

toe, failure point

Motor nerves exiting the spinal cord at the ___ roots carry the ____ copy of the motor command.

ventral, efferent