Biomechanics 1 Review PDF

**[REVIEW OF LEVEL 1]** Try to recall what you remember about the following concepts you learnt about in level 1  ** **The 4 Principles of Stability  ** **Correct force application for take-offs, landings & generating angular momentum (6 factors)  ** **Inertia, velocity & momentum  ** **Wha...

**[REVIEW OF LEVEL 1]** Try to recall what you remember about the following concepts you learnt about in level 1  ** **The 4 Principles of Stability  ** **Correct force application for take-offs, landings & generating angular momentum (6 factors)  ** **Inertia, velocity & momentum  ** **What is determined at the moment of take-off?  ** **Acceleration  ** **Action-reaction (3 factors) & ground reaction forces   ** **The main concepts in rotation -- Angular momentum, moment of inertia, angular velocity & -conservation of angular momentum  ** **factors to consider in descending and ascending swings **[ADVANCED SWING ELEMENTS]** All human motion is a result of - Muscle contractions = FORCE - About joints = ABOUT AXES - Move body segments = ACCELERATES LEVERS **[MECHANICS OF ROTATION SWING]** The gymnast should maximize (optimize) angular momentum at bottom of swing. On downswing, gravity provides the turning force (torque).  ** ** ** **Gravity should act over longest possible time   ** **Gravity should act as far from axis (bar) as possible   ** **Gymnast should minimize frictional forces On upswing, the angular velocity is increased by bringing the centre of mass closer to   the axis of rotation (bar). **[MECHANICS OF SWING]** **Swing is rotation about an external axis.**  1. com max distance from bar 2. com max distance from bar 3. max hip flexion for max angular velocity and bar deformation 4. maintain tight pike for longest time for high angular velocity and keep com near bar 5. extend to straight only for bar reaction forces **[HANDSTAND TURNING ELEMENTS]**  The turns must be initiated on the up-swing and completed in handstand.  The feet should turn towards the twisting direction.**\ **  This action results in an opposite turn of the upper body which applies an "indirect" force on the bar which in turn provides a reaction force in the desired direction.  The body is aligned over the support arm.**\ **  This reduces the moment of inertia about the twisting axis.   In addition, the free arm pushes off the bar to generate torque in the desired direction. **[MECHANICS OF TURNING ELEMENTNTS ]**  1. maximum downswing parameters and load bar 2. turn feet in direction of turn for reaction torque 3. bar returns elastic energy 4. align body over support arm for small moment of inertia 5. push off arm to shift com and odd centre force 6. body straight throughout 7. shift weight to other arm and push to provide off centre force **[THE TWISTING ILLUSION IN GYMNASTICS]**  Many turning skills (round-off, clear hip circle 1/1 turn, etc.) turn ½ on the upward phase and ½ in handstand.  A turn in handstand on the left arm is a right turn and vice versa.  In a round-off, if the right hand goes down first, it is a left turn.  In a clear hip circle with 1/1 turn to left, the 1st half turns on the left arm and the 2nd half must turn on the right arm so that the entire skill turns to the left. **[ANOTHER EXAMPLE OF HANDSTAND TURNING ELEMENTS]**  The turns must be initiated on the up-swing and completed in handstand.  The feet should turn towards the twisting direction.     - This action results in an opposite turn of the upper body which applies an "indirect" force on the bar which in turn provides a reaction force in the desired direction. Feet turn to the Left, so upper body turns to the Right.    BAR CONSTRAINS REACTION    Reaction force of upper body to the Right then becomes the "indirect" action force and the resulting reaction is for the lower body to turn to the Left.  The free arm pushes off the bar to generate torque in the desired direction.  The body is aligned over the support arm.     - This reduces the moment of inertia about the twisting axis. **[FLIGHT ELEMENTS]** **[MECHANICS OF FLIGHT ELEMENTS]** **[RELEASE]**  Body Action is accompanied by reaction that is constrained by contact = indirect   force applied to apparatus = desired "ground" reaction force.  All important parameters are determined here:  rotation, trajectory, height, time, body shape. **[FLIGHT PHASE]**  Angular momentum cannot be changed, but straight body gives potential for increased angular velocity.  Twisting techniques apply. **[REGRASP]**  Attempt to reduce Angular velocity about All axes.  Reduce momentum over greatest time/distance **[INDIRECT GROUND REACTION FORCES -IN CONTACT WITH THE BAR-]** When in contact with the bar, a body action will want to result in the same reactions we have analyzed in Level 1. However, reaction cannot occur because of the constraints of the bar. Therefore, the reaction serves as an action force against the bar which results in an equal and opposite 'ground' reaction force ('bar' reaction force). A cartoon of a child doing yoga Description automatically generated  For flight elements, we want always to use effective body actions to apply the optimal "indirect" force to the bar in order to generate the optimal ground reaction force. **[TAKE-OFF]** At the instant of take-off, these are determined: Path of centre of mass (trajectory)   Angle of take-off and landing (of C of M)   Vertical velocity up (reduced to zero by gravity)   Vertical velocity on landing  = initial vertical velocity   Horizontal velocity   Height (= time)   Distance   Direction Time in the air (= height) Angular Momentum\   (body shape = potential to change speed of rotation) Most errors occur at take-off and are usually due to incorrect force application. Vertical velocity determines height and time in air. **[MECHANICS EXAMPLE OF RELEASE REGRASP ELEMENTS]** 1. straight body means force is far from axis of roation 2. pre -- stretch timing and load bar 3. dynamic hip extension results in extension of upper body. The force on the bar results in a reaction force to assist forwards rotation 4. straight body = max moment of inertia 5. pike, straddle, arms and head in all increase angular velocity 6. extension reduces angular velocity before re-grasp **[DISMOUNTS -- FROM UNEVEN BARS AND HORIZONTAL BAR]** **[RELEASE]** \- Body Action is accompanied by reaction, but constrained by contact = indirect   force applied to apparatus = desired "bar" reaction force. \- All important parameters are determined here:  rotation, trajectory, height, time, body shape. **[BAR ELASTICITY]**  - The deformation and restoration of The bar can dramatically affect The forces  applied to The gymnast and The flight path of The dismount. **[FLIGHT PHASE]** \- Angular momentum cannot be changed, but straight body gives potential for increased angular velocity. \- Twisting techniques apply. **[LANDING]** **-** The gymnast applies forces to reduce Angular and linear momentum to zero. **[EFFECT OF CHANGING RELEASE HEIGHT ]**  The centre of mass of a rigid body will fly at a tangent to the arc of the swing (90° to the radius).  This is an important consideration but gymnasts can apply forces just before release to somewhat modify this effect. In addition, the elasticity of the bar can modify the effect.  Angular momentum is Conserved (stays the same) in the air. If the rotational momentum is set, then nothing the gymnast does can change that total. But the gymnast can change body shape which is equivalent to changing the Moment of Inertia. \ \ (Straight to tuck position; bring arms closer to the body during twisting elements) In order for the rotational momentum to stay the same, the change in Shape (Moment of Inertia) must be accompanied by an opposite change in Speed of rotation (Angular Velocity), i.e.   decrease/shorten the shape = increase speed   increase/lengthen the shape = decrease speed ### ### ### ### ### Inter-segmental transfer of Angular Momentum   There are 3 possible actions in the air... ### ### **[UNDERSTANDING INTER-SEGMENTAL TRANSFER OF ANGULAR MOMENTUM (SECONDARY AXIS)]** ### ### Explanation \#1: For every action there is an equal and opposite and simultaneous reaction. 1. If a gymnast overbalances, rotate arms and legs in the direction of the fall (about a parallel axis).  This causes the rest of the body to rotate in the opposite direction  - overcoming the tendency to fall. 2. This is a normal body reflex to overbalancing, but it can be specifically taught to be more effective.  3. This action is most effective if the introduced rotation has the greatest angular momentum (straight and fast limbs) and is far from primary axis. The effect stops as soon as the arm and leg rotation stops. ### ### ### ### ### ### ### Explanation \#2: In the air, the total body Angular Momentum is fixed. 1. Since the total angular momentum of a body cannot change during flight, if one body part introduces an additional component of AM about a parallel axis, then the AM of the rest of the body must be reduced. 2. Such actions are often normal body reflexes to over-rotation, but they can be specifically taught to be more effective.  3. This action is most effective if the introduced rotation has the greatest angular momentum (straight and fast limbs) and is far from primary axis Rapid rotation of arms forward reduces forward angular momentum of body -- in the air and after landing.