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ESS 303 – Biomechanics

This overview of biomechanics focuses on the neurological system, specifically motor units. It explains the all-or-nothing principle, recruitment patterns, and rate coding that leads to muscle force generation. Different types of motor units—slow, fatigue-resistant, and fast, fatigable—are explored in detail. Key concepts such as the neuromuscular junction, proprioceptors, and the stretch-shortening cycle are discussed, highlighting their roles in effective muscle contraction and flexibility. The session culminates in a look at Proprioceptive Neuromuscular Facilitation (PNF) stretching techniques to enhance flexibility.

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ESS 303 – Biomechanics

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  1. ESS 303 – Biomechanics The Neurological System

  2. Motor Units • A motor nerve and ALL the muscle fibers (cells) it innervates • All or nothing – force and unit size • Recruitment patterns • From small to large • Rate Coding: higher rate  higher force

  3. Size of Motor Units

  4. Size of Motor Units

  5. Motor Units (Cont.) • All fibers in a motor unit are of the same type: • Slow (S): type I, slow conduction & contraction times • Fatigue Resistant (FR): type IIa, moderate Contraction time • Fast Fatigable (FF): type IIb, high conduction velocity and high speed of contraction

  6. Wave of Depolarization

  7. K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ Wave of Depolarization Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+

  8. - - - + + + + + + - - - Wave of Depolarization + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + +

  9. The Neuromuscular Junction Mitochondria Presynaptic Membrane Synaptic Vesicles Sarcolema Postsynaptic Membrane Synaptic Cleft Junctional Folds

  10. Electromyography (E.M.G.)

  11. Motor & Sensory Neuron Anatomy

  12. The Spinal Cord

  13. The Spinal Cord

  14. Proprioceptors • Muscle Spindles: Length • Golgi Tendon Organs: Tension • Pacinian Corpuscles: Pressure

  15. Muscle Spindle Structure

  16. The Stretch-Shortening Cycle • Elastic qualities of muscle tissue and tendons • Greater contraction force possible if muscle is put “on stretch” with an eccentric contraction just prior to a concentric contraction • Examples: Running, vertical jumps, wind-ups, etc. • The neurological component

  17. Proprioceptive neuromuscular facilitation (PNF) Stretching • Currently the fastest and most effective way known to increase static-passive flexibility • A muscle group is passively stretched, then contracts isometrically against resistance while in the stretched position, and then is passively stretched again through the resulting increased range of motion • Fatigue of stretch-reflex (from muscle spindles) and use of IPSP from GTOs

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