Kinesiology 384 Final Exam Review Questions Ch 12-23

Chapter 12

What is anthropometry?

The measurement of the human body. In biomechanics, we are mostly concerned with segment mass, COM, moment of inertia, but it can just include measurements of dimensions of body segments

Segment mass

the mass of a segment (kg)

Segment center of mass

a location on the segment for which the mass of it is equally distributed throughout (m)

Segment moment of inertia

the resistance of a body to rotation about a given axis (kg.m2)

Whole body center of mass

center of mass of a system of articulated rigid bodies (m). a subject is often divided into a number of articulated rigid bodies

What is the procedure for computing the location of the center of mass of a system of rigid bodies?

You need the mass and COM of each rigid segment; the calculation is equivalent to computing a weighted mean; X and Y direction: (1/mass of whole) x sum (mass of segment x COM of segment);

What is the procedure for computing the moment of inertia of a system of rigid bodies about the center of mass of the whole system?

You need: mass, COM, and inertia of segments; and COM of whole body; Use equation I (A) = I (CM) + mass x distance^2 and then add those two numbers together

Chapter 13

What classes of methods are available for determination of body segment inertial parameters? Give one example for each.

Simple statistical model (Dempster, 1955)

Complex statistical model (Hinrichs, 1985)

Geometric model (Hanavan, 1964)

Imaging techniques (Martin, 1989)

What are the drawbacks of cadaver based techniques?

storage of cadavers; cause of death of individuals; age range of potential cadavers; genders of cadavers (all were male); applicability to live population, especially sports people; variations in dissection techniques; low number of participants

What shapes could be used for a geometric solid type model? Give an example.

Truncated cones (limbs: foot, shank, thighs, forearm, upper arm)

Spheres (hands)

Cylinders/Elliptical discs (trunk)

Ellipsoid (head)

List the advantages and disadvantage of imaging techniques for the determination of body segment inertial properties.

Advantages: subject specific parameters; equipment is becoming much more readily available

Disadvantages: equipment is not ALWAYS available, possible exposure of body parts to radiation, data reduction is time consuming

Chapter 14

What is image based motion analysis?

A system records images of the activity from which measurements are made. These measurements can be film images or video images for example

What does calibration refer to in a motion analysis context?

determining the relationship between image coordinates and object space coordinates

What does reconstruction referto in a motion analysis context?

determining the location of points in object space from image coordinates; real coordinates are reconstructed from image coordinates

What are the different kinds of systems available for motion analysis?

Manual Digitization (Cine/Video)

Automated Systems (video bases w/ passive markers/LED based systems)

What assessment criteria should be used when evaluating systems for motion analysis?

Accuracy: difference between the measured values and the true values of criterion data; LED bases systems (automated)

Precision: the different between the measured value and the expected mean value

Resolution: the least discernible change that measurement systems can measure

Sample rate: how many images/frames does the system do per second; LED based systems (automated)

Markers: required or not? what type? how are they tracked? Passive markers (automatic video - marker system) OR LED based systems (for tracking)

Sometimes, flexibility as well: film/video with manual digitization

Chapter 15

What are the sources of noise in motion analysis?

Systematic Erros: in some correlation with the measurement process or movement, such as:

• some operation errors; incorrect marker placement; marker movement; calibration errors

Random errors: errors that are random or stochastic, such as:

• some operator errors; some aspects of marker movement; rounding errors in computer artihmatic

How can noise be removed?

noise cannot be fully removed but can be minimized via:

• following careful experimental protocols

• processing of the data to reduce noise (butterworth filter and quintic spine)

• data differentiation magnifies sound, not reduces

What does the process of differentiation permit?

displacement to go velocity OR velocity to go to acceleration (integration is the reverse of differentiation)

• differentiation tends to AMPLIFY noise so it is important to reduce noise as much as possible prior to performing it

List six criteria which would be useful for evaluating an assessment protocol.

1. Do the parameters/variables examined relate to the performance

2. Could the coach/athlete/physician/patient observe the parameters/variables anyway?

3. Do the parameters/variables clearly distinguish between good and bad performance?

4. Does the analysis procedure alter performance?

5. Are all the measurements accurate and reproducible?

6. Are the results understandable by performer, coach, or clinician?

Chapter 16

What are the key design specifications for a force plate?

• light

• rigid

• strong

• high natual freuency

• imperceptible displacement

• no cross-talk between axes

• easy and stable calibration

• suitable recording system: HIGH sample rate; sufficient storage capacity

What is the source of the ground reaction force?

The source of the ground reaction force is the individuals weight (mass AND gravity) because it exerts an equal and opposite force back

What are the problems when using a force plate?

• Size: they are generally small in size (but if the force plate gets much bigger, the frequency will get lower)

• Surface: the top of the plate is metal, which is NOT a typical surface for many activities

• Ringing: some times the plate vibrates when the subject strikes the place, which interferes with measurement procedure

What applications can force plates be used for?

• Gait analysis: key tool used to discern sources of gait abnormalities

• Shoe design: used to see forces experienced during running, and how different shoes change it

• Postural studies: analysis of standing - what forces occur? how do these forces vary under clinical conditions?

• Diving: GRF have been measured at takeoff during dives from 10 m towers

In what other ways can force be measured?

• Gymnastic equipment: the high bar and rings have both been instrumented

• Tendons of cats: to examine forces during locomotion, force transducers have been fitted to tendons of cat

• Human achilles tendon: due to relative ease of accessibility, the human Achilles has been instrumented

• Prostheses: to assess the loads they must bear

Chapter 17

Outline a possible mechanism for injury involving forces.

• Separate genetically similar limbs into higher impact forces OR lower impact forces

• Large forces (GRFS) --> trabecular micro-fracture --> bone remodeling --> resultant stiffening of bone --> increased stress on articular cartilage --> cartilage breakdown --> joint degradation

What is the role of running shoes?

Running shoes are shock absorbers

What is a rear foot striker? What does this mean about their impact peaks compared to mid-foot strikes?

Rear foot strikers mean the individual lands on the rear third of their foot while running

• The impact peak is much LARGER in rear foot strikers than mid-foot strikers

What is impulse? In high jumping, what would the athlete endeavor to do with their impulse and how?

the product of force and time OR the area under the force-time curve OR change in momentum (mass x velocity)

(Positive (+) impulse: high velocity and vice versa)

• A high jumper would want to create a positive or higher impulse to maximize the height of the jump

Chapter 18

What are the component parts of the resultant joint movement?

Number of moment arms, and forces produced by muscles, ligaments and articular contact

Why is human musclo-skeletal system said to be interdependent? (Also called redundant).

because there is generally always more than one muscle that can produce a moment at a joint

What is co-contraction? When might it be used?

when there is activity of agonists and antagonists simultaneously

may be used in the following ways:

• Priming agonist muscles: prior to landing, the agonists can be preactivated by contracting against the antagonists to resits motion

• Stopping joint rotations: during fast joint extensions, the antagonists are activated to stop joints from being over extended

• Biarticular muscles: certain muscles span two joints and require co-contractions of other muscles to act (to prevent gastric groups from working both joints, vasti- groups turn on while running)

What are the advantages of having a redundant system?

Muscles can share load; can share fatigue; useful if one muscle gets injured; muscles tend to have different specializations and secondary actions

How can an EMG aid in the understanding of the role of muscle in human movement?

can help understand the individual muscle forces, which would give insight into the etiology of injuries and the training of muscles for sport or rehabilitation

• Give indication of which muscles are active, but will not give clear indication of relative activity

Chapter 19

Describe the basic structure of muscle.

Muscle --> fascicle --> muscle fiber --> myofibril (a single muscle fiber) --> actin (thin)/myosin (thick)

What is the force-length relationship of the muscle fibers? What is this caused by?

As the length of the muscle fiber changes, so does the force

• the optimum muscle fiber length is around 2.2 um and as it gets larger/smaller, the force decreases

• Shortening of muscles: caused by interference between cross-bridges

• Lengthening of muscles: some cross bridges are too far apart

What is the force-velocity relationship of muscle? What happens during the eccentric phase? Based on whose work is the equation commonly used to describe the concentric phase of the force-velocity relationship?

• Concentric muscle action: as velocity INCREASES, the force DECREASES as time for formation of cross bridges is reduced

• Eccentric muscle action: as velocity INCREASES, the force also INCREASES

• the maximum isometric force is 100% force at 0 velocity

• maximum velocity is at the right most side (short)

• Hill (1938) proposed an equation to represent the concentric phase of this relationship (based off of cross bridge theory)

What are the key properties of tendon?

• Tendons are assumed to be rigid, but they are not

• more force exerted on it, the longer it will be (until a certain point) -- storing energy

• once tendon starts to shorten, get back the stored energy, but NOT all of it

What are the sources of the passive movement at human joints? How might this passive moment be of use?

The sources of passive moment at joints are: joint capsule (47%), muscles (passive; 41%); tendons (10%); skin (2%) -- largest towards the extremes of the range of motion

• Passive movement might be of use because they are the first to respond during unexpected events (safety mechanism)

What are the implications of the moment arms of muscles varying with joint angle?

When the moment arm changes with joint angles, there is a variation in the size of the arm (flexed/extended) in response

Chapter 20

Why when examining human neuro-muscular skeletal system is it necessary to resort to a modeling approach?

The models of muscles can be used to study properties of isolated muscle, simple single joint actions, complex whole body movements and can give insight into:

• how muscle properties dictate performance, optimum performance, influence of surgery, and why movement is coordinated in certain ways

What insight did the study of Bobbert et al. (1987) give into the role of the human gastrocnemius in vertical jumping?

The Bobbert study revealed that the gastrocnemius is co-activated with the knee extensors (during vertical jumping) to transfer power from the thigh to the foot -- causes greater force at foot (since higher velocity)

• Gastrocnemius can transfer power without shortening itself

What compromise must the human musculo-skeletal system deal with when high jumping?

Musculo-skeletal system has to find a compromise between run up time (speed) and angle of knee; optimum performance for a knee angle of 45-50 degrees and run up velocity of 6.7 m/s; We want high impulse to jump high. If we have a high run up velocity, the time is greatly reduced

Compare three models of varying complexity. What are the relative merits of simple versus complex models?

Simple: easily duplicated and easier to interpret; yields better results

Complex: takes more time to run and interpret results from experiment

Chapter 21

What evidence is there for mechanical energy storage during human movement?

Cavagna's study provided evidence for energy storage during human movement (running) b/c he estimated the cost of running should be 460 Joules/m, but the subjects only used 300 Joules/m

Potential sites of mechanical energy storages

tendons and muscle fibers

Define elasticity. How are the equations for a spring useful to explain energy storage?

the property of a material which makes it return to its original shape after being deformed by a force; Equations are useful to explain energy storage b/c it can be rearranged to L = c x F to determine the change in length of a tendon

Tendon can be an efficient energy store, give an extreme example and explain how this helps to save chemical energy.

The camel plantaris runs from behind the knees to the toes. The muscle belly is usually 2mm and the tendon is 1300mm long, so it controls the majority of the storage of energy

During human running, describe two sites of elastic energy storage.

achilles tendons and muscle fibers

Chapter 22

Using bungee jumping as an example, why and how should the stiffness of sports and other equipment be "tuned" to the athlete using them?

The time to stretch the bungee depends on the stiffness of it and the subjects mass.

• If you sent a 50 kg and 100 kg subject bungee jumping, with the same stiffness of 200 N/m, the 100 kg person would take more time to fully stretch the chord, meaning they could hit the ground before rebounding

How is elastic energy storage used in pole vaulting?

The fiber glass pole deforms (stores energy) when the athlete plants it, and recoils (returns energy) as the athlete reaches the top of the vault

Describe what a countermovement is. What are the potential sources of enhanced performance from performing a counter movement?

a movement in the opposite direction before moving in the required or anticipated direction (counter movements often proceed a vertical jump or bat swing in baseball)

• more force, greater velocity, or greater efficiency

• release of elastic energy, interaction between tendon and muscle fibers, neuromuscular potentiation

Using jumping as an example, explain how energy could be stored during a jump involving a counter movement. Why might landing from a drop permit an even higher jump than achievable using a counter movement?

by first bending your knees and pushing into ground before jumping up. This would drop COM by about 30% about would store that much extra energy

Landing from a drop would permit an even higher jump than a countermovement because you drop your COM by an even higher percentage, storing more and more energy

Chapter 23

Describe the cyclical process of the scientific method.

theories need to be constantly reevaluated and adjusted

What are the phases in the development of a model?

1. definition of the problem: what it is that you are trying yo investigate

2. Statement of assumptions: ex. segments are rigid bodies acting about frictionless joints

3. Formulation of system equations: F=ma

4. solution of system: yield output parameters given input parameters

5. Validation: correlation of model prediction with experimental results. This stage may suggest refining and returning to stage 2 or 3

6. Stimulations: examine the behavior of modeled system under a variety of conditions

What are the advantages of doing experimental work over modeling work?

• allows you to see if the predicted model is effective and validated

• Experiment = poor control/perfect model

• Simulation (model) = excellent control/imperfect model

What are the relative merits of a complex and simple model?

Simple models: simple to formulate, simulation is not too confusing, parameters are few and easy to determine, and it is easy to interpret overall

Complex models: complex to formulate, simulations can be time consuming, many model parameters that are hard to determine, and it is hard to interpret overall