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Motion Capture

BIOMECHANICS. Motion Capture. The mean values of max moment of force. T – trunk, El – elbow, SH – shoulder, Fl – flexion EX extention. The mean values of hand grip. Endurance = fatigue resistance. Conclusions.

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Motion Capture

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  1. BIOMECHANICS Motion Capture

  2. The mean values of max moment of force T – trunk, El – elbow, SH – shoulder, Fl – flexion EX extention

  3. The mean values of hand grip Endurance = fatigue resistance

  4. Conclusions • To prevent from loose of your strength try to avoid extreme joint angles! (muscle will be close to its limit – see figure). • For the slow movements of large amplitudes use arm, while the fast ones of small amplitudes are best suited for the fingers! • Practice should focus oncomplete repetitions of the whole skill performed at submaximal speeds – improvement should occur with many repetitions, while gradually increasing speed (segmental interaction – acceleration of proximal segment (arm) -> acceleration of the distal segment appears (hand with sticks). • Listen to your body – there is a lot of signals coming from it (receptors in the skin, muscles, joints, tendons), don’t ignore them!

  5. Muscle force vs. lenght of muscle daily activities Optimal length of the muscle

  6. PROPRIOCEPTIVE SYSTEM is responsible for collecting information about the body itself: from within the body, largely from the muscles and joints. Skin receptors Muscle spindles Golgi Tendon Organs

  7. 4 degrees of freedom 240 degrees of freedom Kopar Degree of freedom –movement in a plane. Human body = a system of body links which form one or more kinematic chains.

  8. First PHOTOGRAPHY second part of XIX century = a turning point in refers to human body movements. • Photos of running horse (1872), E.MUYBRIDGE applied the techique of sequential photography. The next step was to take lots of pictures by means of 1 camera - E.J.MAREY, that initaited cinematography.

  9. 3D registration of movement by Braune & Fisher (XIX/XX cent.)

  10. Motion trackingormotion capture started as a photogrametric analysis tool in biomechanics research in the 1970s and 1980s, and expanded into education, training, sports and recently computer animation for cinema and video games as the technology matured.

  11. VICON

  12. A performer wears markers near each joint to identify the motion by the positions or angles between the markers. passive marker

  13. Vicon System • Vicon automatically records 3D location of markers as points and in very precise way determines their position in space based on the data achieved from 2D video picture.

  14. JOINT ANGULAR CHANGES/ MUSCLES LENGHT CHANGES

  15. Motion capture • To register the movement - markers should be located in the essential (from animating point of view) places on the actor’s body.

  16. Spatial trajectory of foot movement in the sequency of high legs techniques and stability evaluation based on COM

  17. Hoovering Archer Race walker

  18. -> Gollum’s body - about 300 muscles. -> normal skeleton and system of the muscles; -> motion capture recordings were done - Andy was wearing suit covered with small points. He behaved then as if he was Gollum.

  19. The biggest challenge was Gollum’s face. Side by side shots were shown with Andy and Gollum showing exactly the same facial expressions and speech expressions. - Gollum is probably the most similar to the real actor digital creature, that ever appeared in the film – said Jackson - the film director. Andy Serkis - Gollum

  20. skull caps fitted with a tiny camera

  21. Electromyography (EMG) EMG is a very valuable tool in measuring skeletal muscle electrical output during physical activities.

  22. Electromyography = bioelectric activity of the muscles

  23. Skin surface electrodes • Due to their non- invasive character in most cases surface electrodes are used in kinesiological studies. • For deeper muscles (covered by surface muscles or bones) fine-wire or needle electrodes are inevitable. A free selection of any electrode type is supported by an EMG – (pre-) amplifier. The selection of an electrode type strongly depends on the given investigation and condition.

  24. General considerations • The quality of an EMG measurement strongly depends on a proper skin preparation and electrode positioning. • The recommendations for skin preparation: • to shave the patient if the skin surface at which the electrodes have to be placed is covered with hair. • to clean the skin with alcohol and allow the alcohol to vaporise so that the skin will be dry before the electrodes will be placed.

  25. The Motor Unit • The smallest functional unit to describe the neural control of the muscular contraction process is called a Motor Unit. • Single motorneuron & muscle fibers it innervates

  26. Raw EMG signal

  27. The relationship between EMG input and force output • EMG activation is the preliminary condition for any force development and one can expect a very close relationship between both measures. Indeed, there is a very high correlation between both parameters.

  28. Muscle Fatigue • The surface EMG can also be used as measure of muscle fatigue and recovery. • A major point of interest is the measure of muscle fatigue along with the electromyography. • The change in median frequency of power spectrum density is one of the factors that can be used as an indicator of muscle fatigue (De Luca, 1993).

  29. Force platform =? weight scale

  30. Ground Reaction Force Force platform is used to measure ground reaction force on the base of Newton’s third law: law of reciprocal actions. ‘to every action there is always an opposed equal reaction’ Reaction force What does it mean? the ground is coming back up to you and supporting you with a force equal to that of gravity.

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