Biomechanics Final Exam Review Questions
Draw a typical vertical ground reaction force for a vertical jump. Label the stationary, counter movement, time to take off, flight phase, and landing.
(insert image on p 17-5)
How can noise be removed?
- Careful experimental protocols - Processing of the data to reduce noise Common procedures include: butterworth filter (technique used in electrical engineering) & quintic spline (technique used in mathematics)
Give some examples of sports where there is some allowance for body size.
- Scaled activities: wrestling, weightlifting, rowing - Everyone can do these sports, but weight classes are different
What are the advantages of having a redundant system? (more muscles than required)
- Share load - share fatigue - useful if muscle are injured - muscles tend to have different specialization(moment arms, cross-sectional areas, fiber type distributions all differ)
What are the drawbacks of cadaver based techniques?
- Storage, all cadavers male, age range, cause of death, applicability to live population especially sports people, variations in dissection techniques - Advantages include: individual segments are accessible via dissection, inertial properties can be measured accurately, inertial properties can be measured precisely
What is image-based motion analysis?
- System records images of the activity from which measurements are made. These measurements can be for example film images or video images. - from images of activity provide kinematics
How is elastic energy storage used in pole vaulting?
- The fiberglass pole is an energy store, it deforms (storing energy) when the athlete plants the pole, and recoils (returning energy) as the athlete reaches the top of the vault - Pole vaulter select their poles based on their length and elasticity with selection benign dependent on the vaulter's mass and run-up speed Assumptions: - Pole is 100% efficient - All run-up energy is transferred to the pole - No energy is added during the time the athlete is off the ground - Some sources of mechanical energy is ignored
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 force acting on the jumper is a function of the amount of drop, their mass, and the stiffness of the bungee cord. Note the larger jumper experiences larger forces but this correspond to .78 body weights whereas the lighter jumper experiences 1.10 body weights - A lot of injuries in bungee jumping have occurred because bungee stiffness has not been adjusted for jumper mass. But this tuning of stiffness also has implications for other devices designed to cushion impact for example running shoes
Outline the procedures for computing the whole body center of mass position, and whole body moment of inertia.
whole body center of mass position (p 13-2) - you need: the masses of the segments & the locations of the centers of masses of the segments - the calculation to get the whole body COM is equivalent to computing a weighted mean whole body moment of inertia (p 13-4) - you need: the masses of the segments, the moments of inertia of the segments, the distances from the segment center of mass to the common axis - the moments of inertia can be summed once they are about the same axis
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?
-Counter movement jump: body mass used to store energy/potentiate muscles -The jump heights for the counter movement jumps were 5.5% higher than the squat jumps -Counter movements are an important part of movements -Jumps in which the subjects jump up, after dropping from a height of 0.40m = drop jumps -Drop jump: force due to landing from a drop used to store energy / potentiate muscles -The jump heights for the drop jumps were 11.5% higher than the squat jumps
List six criteria, which would be useful for evaluating an assessment protocol. (p15-6)
1. Do the parameters/variables examined relate to the performance? 2. Could the coach/athlete/clinician/patient observe the parameters/variables anyway? 3. Do the parameters/variables clearly distinguish between good and bad performance? 4. Does the analysis procedure alter the performance? 5. Are all measurements accurate and reproducible? 6. Are the results understandable by the performer/coach/clinician?
muscle states
19-2
fiber types
19-7
What is the source of the ground reaction force(Fr)?
A person standing on the ground is exerting a force down onto the ground, due to their body mass and gravity, the ground exerts a force in the opposite direction upwards. If the center of mass is accelerating then additional forces contribute to the ground reaction force. Stationary: F=mg+Wt, Fr=-F Accelerating: F=mg+ma(cm), Fr=-F
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 Precision - is the difference between the measured value and expected mean value Resolution - is the least discernible change that the measurement system can measure Sample Rate - how many images/frames does the system analyze per second Markers - required or not? What type? How are they tracked? 2D versus 3D - does the system easily allow 3D analysis - 2D analysis requires less equipment, less time, less complex mathematics for reconstruction, less complex mathematics for mechanics - But human movement is not planar!
During human running describe two sites of elastic energy storage.
Achilles tendon - During human running the peak force can easily reach three time body weight - Achilles tendon accounts for most of ankle movement meaning that during the running support phase the muscle fibers do not have to shortened which is energy saving - Therefore achilles tendon: stores and returns energy & allows the muscle to resin isometric thus reducing muscle energy consumption Arch of the foot - Running flattens arch of foot - Arch of foot is an efficient energy store returning 78% of the energy applied to it - Ligaments are identified as the predominant source of this storage (plantar aponeurosis, long and short plantar ligaments, spring ligament) - Energy stored in the arch is not influenced by foot strike pattern but can be influenced by shoe construction - The energy stored makes a small contribution to the energetics of locomotion compared with the achilles tendon
List the advantages and disadvantages of imaging techniques for the determination of body segment inertial parameters.
Advantages: Subject specific parameters Equipment becoming more generally available Disadvantages: Equipment not generally available Possible exposure to radiation Data reduction time consuming
How can the bilateral deficit influence vertical jump performance?
Bilateral deficit - the muscular force produced when using two limbs (bilateral action) is less than the sum of the maximal unilateral actions (~ 85%) Results: simulation w/out bilateral deficit = 51.1%, simulation w bilateral deficit = 58.8% Conclusions: - The height of the two legged jump versus the one legged jump is dictated by the bilateral deficit. - Why were moments much smaller in two legged jumps compared to the one legged jumps? The movement was faster so the muscles operated on a less favorable part of their force-velocity curve but jumps were higher as two legs contributed to jump performance.
What does calibration and reconstruction refer to in a motion analysis context?
Calibration - determines relationship between equipment output and quantity to be measured (Ex. a spring used to measure force, as force(a weight) is applied to the spring its length changes) - Cameras must be calibrated prior to measurement - Relationship between points points measured on the image the their real world positions must be determined - Process: record reference, identify image, measures from image (digitize), calibration Reconstruction - Once calibration has been performed then the activity of interest can be filmed/videoed, and key points digitized on the image, and using information from calibration the re coordinates of those points located (objects space coordinates). The object space coordinates are reconstructed form the image coordinates - 2D analysis - one camera sufficient - 3D analysis - at least 2 synchronized cameras required - Process: record activity, identify image, measures from images (digitize), reconstruction using calibration information
Why when examining the human neuromuscular skeletal system is it necessary to resort to a modeling approach.
Can be used to study: - Properties of isolated muscle - Simple single joint actions - Complex whole body movements Can give insight into: - How muscles properties dictate performance - Optimum performance - Influence of surgery - Why movement is coordinated in certain ways
What is co-contraction? When might it be used?
Co-contraction - this occurs when there is activity of agonists and antagonists simultaneously (agonist - muscles the initiate and carry out desired motion, antagonists - muscles which oppose actions of agonist muscles) Useful in: - Priming agonist muscles: prior to landing the agonists are preactivated by contracting against the antagonists. This helps to allow for delays in muscle being ready to resist motion due to activation times - Stopping joint rotations: during fast joint extensions, near the end of the motion the antagonists are activated to stop joints being over extended - Biarticular muscles: certain muscles span 2 joints, and often require co-contractions of other muscles to act
Describe what a counter movement is. What are the potential sources of enhanced performance from performing a counter movement?
Counter movement: (aka stretch shortening cycle) - A movement in the opposite direction before moving in the required direction - Ex. in running where during landing the muscle tendon complex is stretched, and the shortens during the push-off - Results in enhanced performance (action could have more force, greater velocity, or greater efficiency) Potential sources: (read more on 22-6) - Release of elastic energy - Interaction between tendon and muscle fibers - Neuromuscular potentiation
How can EMG aid in the understanding of the role of muscle in human movement?
EMG - measurement of the electrical activity of muscles associated with the activation. Electrodes are placed on or in the muscles to measure the electrical activist. Will give indication of which muscles are active, but does not give clear indication of relative activity Problems with EMG: EMG is very noise sensitive, cannot always access muscles of interest, EMG activity is not always indicative of significant amounts of muscle force, restrictive for certain movements
Define elasticity. How are the equations for a spring useful to explain energy storage?
Elasticity is the property of a material which makes it return to its original shape after being deformed by a force. Energy being put into the material is returned during unloading. Equations for spring 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 - Length is directly proportional to force Hyrestisis?
What shapes could be used for a geometric solid type model? Give an example.
Elliptical disc, truncated cone, stadium solid Cylinder can be used to model a forearm or foot
What evidence is there for mechanical energy storage during human movement? What are the potential sites of mechanical energy storage in the human body?
Evidence: - 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 - Energy experienced during running was less than predicted so energy must be stored mechanically Potential sites: tendons and muscle fibers
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 designs change this Postural design - analysis of standing, what forces occur, how do these vary under clinical conditions Diving - ground reaction forces measured in 10m tower ar Diving World Championships
What are the potential limitations of goniometers and accelerometers?
Goniometer - measures angles Potential limitations: - Attachment to body - Encumbrance - Data recording Accelerometer - measures accelerations Potential limitations: - Attachment to body - Encumbrance - Data recording - Only provides on kinematic variable - Gravity
In what other ways can forces be measured?
Gymnastics equipment - the high bar and rings have both been instrumented Tendons of cats - to examine forces during locomotion force transducers have been fitted to cat tendons Human achilles tendon - due to relative ease of accessibility the human Achilles tendon has been instrumented Prostheses - limb prostheses have been instruments to assess the load they must bear
What is impulse? In high jumping what would the athlete endeavor to do with their impulse and how?
Impulse: is the product of force and time (units N.s.). Given a ground reaction force it is the area under the force time curve, this area is easily measured using a computer Impulse = change in momentum Momentum = mass x velocity Impulse = change in mass x (final velocity - initial velocity) Therefore: impulse = change in velocity - Positive impulse causes an increase in velocity - Negative impulse cause a decrease in velocity High jump: have as much positive impulse as possible, creates highest velocity
Why is the human skeletal system said to be indeterminate? (Also called redundant)
Indeterminacy is when a system is over specified, that is you have more things than you need to complete the task The human musculoskeletal system is indeterminate because as there is generally more than one muscle which can produce a moment at a joint. It is generally "impossible" to compute how the generation of a given moment is distributed between a group of muscles.
Describe the basic structure of muscle?
Insert image p-1 The following levels of organization can be considered: - Muscles - Muscles are composed of fascicles - Fascicles consists of bundles of fibers - A fiber consists of bundles of myofibrils - Each myofibril ("muscle threads") are composed of sarcomeres arranged in series - Myofibrils contain two important proteins: myosin and actin
What are key properties of tendon?
Key properties: Tendon tends to snap when stretched by about 8% of its resting length At maximum isometric force tendon stretched by about 4% note: tendons are not rigid! force exerted on it by the muscle fibers will cause it to stretch (tendons exhibit a small hysteresis, a difference between the curves during loading and unloading. the hysteresis is small for a tendon because it is an efficient energy store)
Outline a possible mechanism for injury involving forces
Large forces (GRFs) → trabecular microfracture → bone remodeling → resultant stiffening of bone → increased stress on articular cartilage → cartilage breakdown → joint degeneration
What are the key design specifications for a force plate?
Light - aids with portability Rigid - should provide a solid support surface High natural frequency - so its natural frequency is distinct from the frequency of the forces to be measured Strong - able to withstand the potential loads which might be applied to it Imperceptible displacement - the displacement is required to measure the forces but must be small otherwise the movement pattern might be altered No cross-talk between axes - forces in each axis direction shoulder measured distinctly Easy and stable calibration - this helps with conducting data collection in a timely manner Suitable recording system - data are recorded by a computer, these must be an appropriate interface to the computer
What is anthropometry?
Measurement of the human body Normally requires the following biomedical analysis: - segment mass - location of center of mass - moment of inertia These properties of a rigid body are often referred to as inertial properties, or the body segment inertia properties (BSIP)
What are the phases in the development of a model?
Model: - a representation of the essential aspects of a system (e.g. muscle, human body) in a usable form (e.g. set of equations) - Advantages: strict control of variables possible - Limitations: artificial representation (too simple) Phases: 1. Definition of the problem - what is it you are trying to investigate 2. Statement of assumptions - for example, segments are rigid bodies acting about friction-less joints 3. Formulation of system equations - for example F=ma etc. 4. Solution of system - yield output parameters given input parameters 5. Validation - Correlation of model predictions with experimental results. 6. This stage may suggest model refinements and therefore a return to stage 2 or 3 6. Simulations - examine the behavior of modeled system under varying conditions Note - stages 3 and 4 require computerization
What are the sources of noise in motion analysis?
Noise - random fluctuations in a signal which are superimposed on the true signal, corruptions in the data - sample signal = true signal + measurement errors Where they come from Systematic - errors which in some way are correlated with the measurement process or correlated with the movement - e.g.: calibration errors, incorrect marker placement, marker movement, some operator errors Random - errors which are random, often just referred to as noise e.g.: some operator errors, some aspects of marker development, rounding errors in computer arithmetic
What is a rear foot striker? What does this mean about their impact peaks compared to mid-foot striker?
Rear foot striker - rear third of foot Middle third of foot - mid foot striker Front third of foot - fore foot striker (rare) impact peak mid - impact peak is diminished but active peak is slightly linger rear - impact peaks is sharper/higher/larger (insert image on p 17-4)
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?
Relationship: The force-velocity properties of muscle are due to rate at which the myosin cross-bridges can cycle Phases: Concentric muscle action - a muscle shortening to produce force (+tive velocity). As velocity increases the force decreases as time for formation of cross-bridge is reduced. Eccentric muscle action - a muscle lengthening to yield to a force (-tive velocity). As absolute velocity increases force increases. Equation: Hill (1938)
What are the component parts of the resultant joint moment?
Resultant joint moment - is the net effect of the moments about a joint due to all structures crossing that joint, including muscles, ligaments, and bones forces. Component parts: Tj - resultant joint moment NM, NL, NC - number of muscles, ligaments, and articular contact points Rmi, Rli, Rci - moment arms of the muscles, ligaments, and articular contact points Fmi, Fli, forces produced by muscles, ligaments, and articular contact points
Why should sample rate be carefully selected?
Sample rate - the number of samples per second, which is normally measured in Hertz, one hertz is one sample per second, high speed = high sample rate
What is the role of running shoes?
Shock absorption
What are the relative merits of complex and simple models?
Simple models - Simple to formulate - Simulation not too time consuming - Parameters are few - Parameters easy to determine - Easy to interpret - May not be appropriate for complex systems Complex models - Complex to formulate (more error prone) - Simulations can be time consuming - Many model parameters - Parameters hard to determine - Hard to interpret - May not be appropriate from simple systems
What classes of methods are available for determination of body segment inertial parameters? Give one example for each.
Simple statistical model (e.g. Dempster, 1955) - Dissected and measured 8 cadavers Complex statistical model (e.g. Zatsiorsky et al, 1985) - Based his equations on imaging data from 100 male subjects, the nonlinear equations capture the relationship between body dimensions and a segments inertial properties Imaging Techniques (e.g. Martin et al., 1989) Geometric models (e.g. Hanavan, 1964) - To avoid dependence on cadaver data some people have determined human body segment inertial parameters by modeling segments as series of geometric solids, density for these values are taken from cadaver data and is normally assumed to be uniform throughout a given segment (page 13-5, section 13.6)
What insight did the study of Bobbert et al (1987) give into the role of the human gastrocnemius in vertical jumping?
Simple, mechanical model - Knee extensor modeled with a spring, gastrocnemius modeled with a wire Experiment: Release spring, model jumps, length of gastrocnemius adjusted for different jumps, height of jumps measures Results: optimum wire length resulted in a jump height twice that of when the wire was slack Conclusions: coactivation of the knee extensors and gastrocnemius is advantageous, as power is transferred from the thigh to the foot
Compare 3 models of varying complexity. What are the relative merits of simple versus complex models? look at models from this chapter in notebook
Simple: Single muscles Focus on limited properties Easily duplicated and easier to interpret; yields better results Simple uses mechanical models Complex: Takes more time to run and interpret results from experiment Complex uses computer models Multiple muscles All properties
What are the sources of the passive moment at human joints? How might this passive moment be of use?
Source - Joint capsule 47% - Muscles (passive) 41% - Tendons 10 % - Skin 2% Use If the body experiences an unexpected perturbation then passive elements respond first (e.g. car crashes)
What are the problems when using a force plate?
Surface - the top of the plate is metal, which is not a typical surface for many activities Size - they are generally small with .40m by /60m being typical. How do you ensure the subject strikes the plate and keeps the movement natural? (as size gets bigger, ringing increases) Ringing - the plate vibrates when the subject trikes the plate, at its natural frequency, these can interfere with the measured forces
There are 2 main sites for potential energy storage: tendons and muscle fibers
Tendon properties: - Passive - Tendon tends to snap when stretched by about 8% of its resting length - At maximum isometric force tendon stretched by about 4% - Tendon can stretch maximally by 6% in vivo - Note: ligaments have very similar properties to tendon Muscle fiber properties - Active, so complex function to describe its energy storage - Site of energy storage are the muscle cross bridges - At maximum isometric force can stretch by about 1.3%
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 A camel's plantaris runs from its thigh to its toes. its muscle belly is short while the tendon is long, allowing it to store a lot of energy elastically so the camel does not have to use as much chemical energy.
What is the force-length relationship of the muscle fibers? What is this caused by?
The force length properties of muscle are due to the amount of overlap between the actin and myosin filaments. Short lengths - cross-bridges interfere with one another, force reduced Long lengths - some cross bridges are too far apart to form, so force is reduced
Explain how the ability to perform pull-ups varies with body size.
The larger the athlete is the harder it is to perform the pull-up TB=(FB)(rB) FB=force due to bodyweight (mg) rB=moment arm of the body relative to the bar because both FB and rB are larger in a taller person than a shorter person, TB is also larger
Describe the cyclical process of the scientific method.
Theories are not proved, but fail to be falsified theories need to be readjusted and evaluated
What does the process of differentiation permit?
To go from displacements to velocities or velocities to accelerations
What are the advantages of doing experimental work over modeling work?
advantages: safe and less time disadvantages: validation is difficult, reliance of math and computers
For 3 sports identify anatomic variations which can confer an advantage in that sport.
deadlifting: long arms swimming: hypermobile knees and ankles, long wing span middle distance track: skinny, not as much muscle mass to move body building: variety in muscle belly / tendon length
What are the implications of the moment arms of muscles carrying with joint angles?
moment arm is greater when the joint angle is greater More force can be produced at a given joint angle because of the distance the force is produced from the axis during joint movement.