KPE 315 Advanced biomechanics "When you can measure what you are speaking about, and express it in numbers, you know something about it." (William Thomson, Lord Kelvin. Popular Lectures and Addresses, 1891-1894). Introduction True science investigates and brings to human perception such truths and such knowledge as the people of a given time and society consider most important. Art transmits these truths from the region of perception. Leo Nikolaevich Tolstoy Perception You teach me baseball and I'll teach you relativity...No we must not You will learn about relativity faster than I learn baseball. --Albert Einstein I was told over and over again that I would never be successful, that I was not going to be competitive and the technique was simply not going to work. All I could do was shrug and say 'We'll just have to see'. --Dick Fosbury won an Olympic gold medal at the 1968 Mexico City Games after he invented a revolutionary high-jump technique. Or do you feel like this … Nobody in football should be called a genius. A genius is a guy like Norman Einstein. --Joe Theismann Introduction Biomechanics – the application of mechanical laws to living structures, specifically to the locomotor system of the human body (Dorllandès illustrated Medical Dictionary) Outline What is biomechanics? Who uses biomechanics? How do biomechnanicsts approach sports movements? Introductory analysis of human movement – “a brain stormer!” Cognitive thinking How useful is a knowledge of Biomechanics? Very useful Not very useful Definitely a pain in the butt! Your answer will determine the application of mechanics in your professional life. The question is - will this course change your opinion?! Physical education teacher Physical education means that the learners individual dimensional needs – physical, intellectual, social, emotional and spiritual – are satisfied explicitly through all forms of physical activity. To the coach From the beginner to elite athlete technique is always part of the coaching program. To the athlete The experimental literature does not cover the value of mechanical analysis for the advanced athlete, but empirical evidence seems to indicate somewhat greater value at the higher skill levels. The Biomechanist Biomechanics aims to explain the mechanics of life and living. From molecules to organisms, everything must obey the laws of mechanics. Biomechanists analyse movement in reference to: Table 1. A schematic of movement characteristic components Time Space Force Abstraction Duration Self Internal-external Quality Sequencing world Biological-physical Time aspects of human movement The duration of human-movement and the separate actions or phases of a movement pattern are usually measured in milliseconds, seconds and minutes. The initial analysis of a movement, is to determine the duration of each body segments displacements. When compared to the total time of the movement, the relationships of displacements with respect to different body parts can be determined. This is known as the sequencing of actions. When time is related to space (3-D) we can determine the positions, displacement, velocities and accelerations of body parts. Spatial aspects of human movement The spatial analysis uses several different spatial frames of reference. For the body it is the anatomical framework. For the World we move in the Cartesian (rectangular with three perpendicular axes x,y, and z) coordinate framework is used. This framework quantifies up-down; forward-back and side-to-side movement. Translatory, rotary motion and general motion Translatory motion is motion from one plane to another, with each part of the body moving an equal distance in a linear or curved path. Rotary motion is the body or body segment rotating around an axis. Human movements are complex and involve a combination of rotation and translation - known as general motion. Axes and planes Three imaginary planes (Cardinal) divide the body in half by mass are known as the: Sagittal Frontal Transverse planes. The Sagittal plane The Sagittal plane divides the body vertically into left and right halves in which forward and backward movements of the body occur The frontal plane The frontal plane splits the body vertically in front and back halves in which lateral movements of the body occur. The transverse plane The transverse plane separates the body into top and bottom halves in which horizontal and body and body segment movements occur when the body is in the erect standing position. Anatomical reference axes When a segment of a human body moves, it rotates around an imaginary axis of rotation that passes through a joint to which it is attached. There are three axes: The Frontal (mediolateral) axis The Longitudinal axis The Anterior-posterior axis The Frontal axis The Frontal axis (mediolateral) is an imaginary line around which saggital plane rotations occur. The Longitudinal axis The Longitudinal axis is an imaginary line around which transverse plane rotations occur. The Anterior-posterior axis The Anterior- posterior axis is an imaginary line around which frontal plane rotations occur. Forces Internal forces – muscle contraction that applies a force to a bone. External force – a force exerted on a body from outside the system, from some other body. Quality How is this defined if the same force and identical movements are produced? What is that innate quality that defines exceptional movement? Different methods for movement analysis Different models for studying movement. Choose one or design your own! POSSUM Factor-results Holistic principle model POSSUM This system uses a number of continuums to describe human movement. Purpose: Projection: height range speed Observation: initial path: vertical 45 horizontal or below System of studying: ROM Speed of motion Understanding: Mechanics of motion Movement: Segment or whole body Factors-results method This is a hierarchical structure to depict factors that determine the movement result. This method will be needed for the presentation (see OH). Holistic – principle method This method aims to accomplish a comprehensive description of movement 1) Describing the movement. 2) Setting the performance goal. 3) Identifying the anatomical, mechanical and environmental considerations. 4) Determining the biomechanical principles for successful performance of movement. 5) Assessing the performance based on these principles. Sports skill analysis Apply the definitions of style, skill, and technique to the following sports movement from the video clip. Definitions Skill - a general movement pattern adapted to a particular activity or sport. Technique - a particular type of movement of the same skill Style - an individual adaptation of a technique. Practical sports movement analysis In your groups determine: • 1) Which movements are personal style? • 2) Define the skill of the movement. • 3) What is the technique used here? • 4) What is the performance objective? • 5) List the constraints associated with the movement. Questions-continued 6) Is the movement occurring in an open or closed environment? 7) Is it a discrete or continuous skill. 8) Describe the arms and legs at take off in reference to their planes and axes 9) List the biomechanical factors, and then the mechanical principles and then note the critical features. (For example for a free throw the biomechanical factor would be optimal force application for accuracy and height , and then the mechanical principles are angle of release, speed of release and height of release and then note the critical features are segmental energy transfer, and arm release angle at 90 degrees.) 10) How would you describe the quality of movement? Cognitive Thinking A cognitive approach requires the following steps that resemble the force-analysis system. Write down the “known” Write down the “unknowns” Draw out the scenario (visual skills used here) Draw a free body diagram. Find the relevant equations and define steps for solving the problem. Solve using cognitive thinking Determine the acceleration of the two masses 4 and 3 kg when a horizontal force of 9 N is applied. Known m1 4.00 kg and m1 3.00 kg F = 9 N Unknown acceleration of system. Draw a free body diagram y F m2 m1 x Find the relevant equations and define steps for solving the problem. F = ma Fx = (system) = Fx = (m1 + m2) a a = F / m1 + m2 a = 9 / 4 + 3 a = 9/7 a = 1.29 ms-2 Sample Question 2 An applied force of 50 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of friction. Use the diagram to determine the normal force, the net force, the mass, and the acceleration of the object. (Neglect air resistance.) Solution Known: F gravity = 80 N, friction force = 10 N and force applied = 50 N Unknown: force normal; mass; acceleration and force net. Apply relevant equations and define steps for solving the problem Since there is no vertical force acceleration, there is no vertical net force. Therefore F normal = Force gravity = 80 N Solution Mass can be calculated by using F = m acceleration (due to gravity) = m = F/ a = m = 80 / 9.81 (you can use 10 for ease) = 8 kg or 8.15 kg. Fnet is the sum of all the force acting on the system In the vertical direction F normal = Force gravity = 80 N In the horizontal direction force applied = 50 N and in the opposite direction Force friction opposes the motion by 10 N. By vector addition 50 N + -10 = 40 N To determine acceleration use F= ma or a = F/m a = 40 / 8 = 5 ms-2.
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