PED 1323 Motor Control & Motor Learning

Contribution of afferent feedback and descending

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Contribution of afferent feedback and descending drive to human hopping. J Physiol. 2010 Mar 1;588(Pt 5):799-807. How does an exercise scientist, PT student, trainer or athlete use a knowledge of stretch reflexes? Description of experiment and results. Subjects perform three of each of the following types of jump: 1. Squat jumps (SJs). The SJ starts with the subject in a squatted position, then the upward jump is initiated. 2. Counter movement jumps (CMJs). The CMJ starts with the subject standing with knees extended, then the knees are flexed followed by immediate knee extension. 3. CMJs starting on a 12 inch elevated platform. The platform start for the CMJ has the student stepping off the block and landing on the floor with both feet at the same time, and then immediately jumping upward. The height jumped is record and there is alternation between jump styles to reduce order effects (fatigue and practice/learning). It is ensured that the subject does not perform any dip movement prior to the SJ. All jumps are completed with the hands over the head before and during the jump (so arm movement does not contribute to jump height and the subjects hands are in position to push the vertex device at the maximum height reached). The maximal jump height is always attempted.
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Motor Control Section 1: The Stretch Shortening Cycle (a.k.a. plyometric movements) Unit 3: Stretch Reflexes Best jump scores: Squat Jump Height Counter Movement Jump Height Block Jump, Counter Movement Jump Height Subject D 3 4 4.5 Subject C 3 5 6 Subject K 2.5 3 2.5 Subject M 8 12 11 Subject S 4 4 4 Q1) Was there an increase with the CMJ compared to the SJ? Q2) If there was an increase, WHY was there an increase? Q3) What was the effect of increasing drop height on jump height?, WHY? Q4) Why might one person produce the greatest jump height from a CMJ starting on the floor, while a second person produces the greatest jump height during the CMJ with a drop off the block? Sensory   events from  external  environment BRAIN & BRAIN STEM SPINAL CORD VENTRAL  ROOT DORSAL  ROOT Segmental  spinal  network M u s c l e Displacement Sensory  consequences  of movement Afferent  input
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Motor Control Section 1: The Stretch Shortening Cycle (a.k.a. plyometric movements) Unit 4: Motor Units MOTOR UNIT = MOTOR NEURON AND ALL THE MUSCLE FIBERS IT INNERVATES MOTOR POOL = THE GROUP OF MOTOR NEURONS THAT INNERVATE ONE MUSCLE Motor neurons vary in SOMA SIZE The number of muscle fibers a motor neuron innervates is the INNERVATION RATIO The average innervation ratio varies between muscles: • one motor neuron innervates 15 muscle fibers (1:15) in the eye muscles • one motor neuron innervates 340 muscle fibers (1:340) in the first dorsal interosseus muscle (hand) • one motor neuron innervates 1,900 muscle fibers (1:1,900) in the tibialis anterior and medial gastrocnemius muscles ALL THE MUSCLE FIBERS OF ONE MOTOR UNIT ARE SIMILAR CATEGORIES OF MUSCLE FIBERS The view , that exists in some “current” text books, such as… Exercise Physiology for Health, Fitness, and Performance (2007) By Sharon Plowman, Denise L Smith
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Motor Control Section 1: The Stretch Shortening Cycle (a.k.a. plyometric movements)
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  • Fall '11
  • John Smith
  • The Land, Motor control, Gordon Chalmers

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