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EXSC 550 EXAM 4 QUESTIONS WITH COMPLETE
ANSWERS
3D kinematics part 1 - ANSWER in comparison to 2d video analyss of movement, 3D analysis involves a much deeper understanding of the body positioning in a given space. Multiple coordinate systems as well as the concept of linear transformation are important to understand when analyzing 3D movement. Common sensors used in 3d data collection - ANSWER Accelerometers, gyroscopes, magnetometers, inertial sensors, linear sensors, electromagnetic sensors, optical array sensors (used in motion capture). although its common to think of 3D analysis of movement only utilizing video motion capture, there are actually many different sensor types that can be used to record a wide range of unique data dets for 3d analysis. these sensors include accelerometers, gyroscopes, inertial sensors, linear sensors, electromagnetic sensors, and array sensors. optical array sensors - ANSWER are the sensors found on high speed optical cameras, such as the Vicon cameras in the Liberty university analysis of human movement labs. these sensors pick up the reflections from retao-reflective joint markers that are placed on the body. joint marker placement will be discussed in greater detail in part two of this. In the LU CAHM lab - ANSWER 4 Vicon T40 cameras, featuring a vicon designed 4. megapixel sensor capable of 515HZ full frame resolution with freeze-frame shutter. Also included is a near-intra-red (NIR) strobe with 56 degree field of view and 18 mm lens. 6 Vicon T20 cameras : featuring a vicon designed 2.0 megapixel sensor capable of 690 HZ full frame resolution with freeze-frame shutter. Also included is a near-intra-red (NIR) strobe with 56 degree field of view and 12.5 mm lens. 2 Bonita 720c Cameras: color reference video cameras, 120 fps, 720p with 4-12mm lens. 16 Delsys Trigno wireless accelerometers camera set up - ANSWER Multiple high speed cameras used, each camera provides a distinctive review and records the 2D location of markers in a camera coordinate system. 3D global coordinates are determined by direct linear transformation (DLT).
Optical cameras are typically set up high above the subject and are placed around the perimeter of the capture volume as shown in the figure on this slide. the joint marker data obtained from each individual optical camera is actually 2D only. it is the computer system that calculates the 3D imaging through the analysis of all of the 2D data from each camera view- a process known as direct linear transformation. coordinate systems - Global or laboratory coordinate system (GCS) - ANSWER XYZ (in capital letters) represent the plane Y axis : directed anteriorly Z axis : directed vertically X axis : directied directed horizontally (perpendicualr to the Y and Z axes) prior to data capture all of the biomechanical tools being utilized must be calibrated and then matched into one coordinate system, the global coordinate system (GCS). the GCS is also known as the fixed or laboratory coordinate system. Calibration into the GCS is performed in order to ensure that the computer knows the correct position of all the biomechanical sensors in referrence to one coordinate system and is then able to create precise 3D positioning of sensors when synthesizing all of the data from all of the sources. coordinate systems - ANSWER Notice that labeled on the GCS XYZ axes are additional letters (i, j,k). these represent unit vectors for the axis they are labeled on. coordinate systems - segment or local coordinate system (LCS) - ANSWER can also be called the moving coordinate system. each joint marker that is attached onto a subject will have its own LCS in the computer. each body segment (represented by the joint marker attached to the subject) is defined by the LCS in the segment. As the body segment moves, the LCS moves respectively. Lower case letters represent the axes (x,y,z. Vecteors i', j',k' 2D vs 3D coordinate systems - ANSWER in 2D analysis, the Y axis is vertical, however, in 3D biomechanical analysis, the Z axis is vertical Right hand rule - ANSWER determines proper direction of positive and negative rotation. With your right hand, point your thumb toward the ceiling and allow your fingers to naturally curve towards the left. your thumb pointing vertical represents the positive Z axis. the curving of the figners toward the left represent rotation in the positive direction (counterclockwise) about the Z axis.
data capture preparation - ANSWER enter the subject name fill in subject parameters place joint markers on subject with the subject standing in the capture volume, record for 2 seconds. this allows the software to auto-label the joint markers pipeline and labeling - ANSWER performed by reconstructing a new pipeline- connects the dots, creates the stick figure. check to make sure all markers are correctly labeled. the stick figure should look visually correct. Run static plug in gait pipeline- this runs operations to generate a LCS on each joint marker dynamic trials - ANSWER you are now ready to capture your subject trials (known as dynamic trials) in 3D. make sure all the appropriate data sources are selected (optical cameras, video cameras, force plates, EMG). Instruct the subject to perform several warm ups before capturing their live performance trial analysis and cleaning - ANSWER open data management load the trial select and run the reconstruct and label new pipeline crop the trial run the dynamic plug in gait pipeline check the quality fill in gaps of missing data with tools
data analysis - ANSWER can view graphs of the data can export data to an excel document to get processed by SPSS can also send the data to other software programs such as Polygon or Visual 3D consideratios right vs left side of the body - ANSWER X axis is inconsistent anatomically between the L and R sides of the body therefore to be consistent with the right-hand coordinate system segments on the R side of body have x-axis in the lateral direction segments on the L side of the body have x-axis in the medial direction X axis example - ANSWER the LCS vectors in the x,y, and z axes are labeled on this figure notice that the force vector i' is labeled in the lateral direction since it is on the R hip. remember i' represents the force vector for the x-axis, j' represents the force vector for the y axis, and k' represents the force vector for the z axis. joint angle measurement challenge - ANSWER joint angles are independent of the position of the origin of the coordinate systems. often the resultant angle is not a vector therefore angles cannot be added or subtracted. some clinical or sport related analyses require the creation of a virtual coordinate system based on a plane of movement or direction of travel. 2D angles in three planes do not equal a 3D angle joint angle normalization - ANSWER referencing a joint angle to a reference posture is referred to as angle normalization ex. all joint angles = 0 in the standing posture all segments are then aligned with the GCS
shaving off body hair the use of swim caps specially designed full body suits (fastskins) ex. speedo LZR: reduced skin friction drag up to 24% drag forces - ANSWER produced by the motion of a body in fluid (water or air) and are responsible for reducing this bodys velocity three types : skin fraction drag pressure drag wave drag pressure drag - ANSWER also called form or profile drag critically affects ball sports, downhill skiers and cyclists influences aerodynamics streamlining - ANSWER incorporate gradual tapering to minimize pressure effect and seperation of fluid a streamlined shape causes fluid movement in layers in the case of a non-streamlined objects, vortices are formed where the fluid does not flow smoothly, resulting in drag the drag is caused by bits of fluid being dragged along with the moving object tips to reduce drag in cycling - ANSWER get out of the wind by drafting behind other riders whenever possible
keep clothing zipped up, relatively snug lower stroke counts lighter wheels make climbing easier consider aero bars to make your ride more comfortable and faster get low when riding against a head wind wave drag - ANSWER the third contributor to the total drage force. it differs from skin friction drag and pressure drag in that it acts at the interface between two different fluids : water and air coefficient of drag - ANSWER a unitless number, an index of the bodys ability to create fluid resistance influenced by the shape and orientation of the body relative to the fluid flow irregularly shaped objects or objects with relatively blunt surfaces have higher coefficients lift forces - ANSWER act perpendicular to the fluid flow these forces may act in any direction due to the fluid flow and the orientation of the object moving through the fluid angle of attack - ANSWER the angle formed by the longitudinal axis of the object and the direction of the fluid it encounters critical in determining the relative amounts of lift and drag forces that will determine the lift/drag ratio encountered by the object bernoullis principle - ANSWER describes the inverse relationship between relative velocity and relative pressure in a fluid flow
Manipulation of other variables decrease mass increase force, time sport examples : long jump, shot put, discuss, javelin, punting primary variable that maximizes results in sports activities - ANSWER throwing activites: velocity jumping: velocity striking or impact activites: force kinetic link principle - ANSWER coordination of body segments to transfer momentum sequential kinetic link principle- sequence of joint rotations leading to high velocity or momentum of the last segment Simultaneous kinetic link principle- major body motions occurring at the same time. each segment producing simutaneous momentum Somersault - ANSWER sprinting - ANSWER two major phases- ground phase and recovery phase (also know as the aerial phase) Sprinting gait cycle- 40% ground, 60% recovery vertical displacement goal - ANSWER primary variable : maximize velocity factors: angle of release
Manipulation of other variables. decrease mass increase force, time sport examples: high jump, pole vault, basketball and volleyball Hip mechanics - ANSWER rapid rotation of the joints neccessary hip flexes in recovery phase hip extends in ground phase max hip flexion position is known as knee lift from a coaching standpoint fast hip extension allows for reduced ground time and increase stride rate angular displacement goal - ANSWER primary variable: maximize engular velocity manipulation of other variables: decrease- moment of inertia increase- time torque Sport examples: Squat, deadlift, overhead press, flys arm in throwing, aerials in gymnastics and diving Overhand baseball throwing - ANSWER somersault - ANSWER to run or jump, turning the heels over the head stride rate trends - ANSWER elite sprinters have greater stride rates than novice sprinters
decrease moment of inertia increase torque, time sport examples: Trunk and arm segments in baseball pitching leg segments in sprinting arm segments in batting extremity segments in striking activities and weight lifting forefront valgus - ANSWER large force application goal - ANSWER primary variable: maximize force manipulation of variables: decrease time increase velocity, mass Sport examples: bat and ball impact in batting club and ball impact in golf racquet and ball impact in tennis hand and ball impact in volleyball fist or foot impact in MMA Foot flare - ANSWER small force application goal - ANSWER primary variable: minimize force manipulation of variables:
decrease mass, velocity increase time Sport examples: catching a ball (baseball, softball, football, basketball) bunting in baseball GRF when landing from jumps Pronation - ANSWER movement that turns the palm down Large torque application goal - ANSWER primary variable: maximize torque around joint manipulation of other variables: decrease moment of inertia increase angular velocity Sport examples: trunk and arm segments in pitching leg segments in sprinting arm segments in batting Supination - ANSWER movement that turns the palm up small torque application goal - ANSWER primary variable:minimize torque around joint manipulation of other variables: decrease angular velocity increase moment of inertia
stride rate and stride length - ANSWER stride rate-the number of strides per second stride length-distance between strides, greater than the runners height in elite 100 meter dash max velocity: 12 m/s average velocity: 10.31 m/s heel whip - ANSWER external rotation of the foot during initial swing would be defined as a medial heel whip pelvic drop - ANSWER hip hikes—is a great exercise to improve the strength of the hips hip adduction - ANSWER the upper leg (femur bone) moves from an outward, inverted-V position inward towards the other leg tibial rotation - ANSWER condition in which the Tibia rotates externally on the femur instead of maintaining a neutral position. Over time this can lead to medial knee pain as the supporting structures are strained and can cause meniscus tearing and ligament damage Toe out angle - ANSWER angle between line of progression and toe
