Biomechanics Russ Ebbets, DC NY Chiropractic College Editor, Track Coach spinedoctor229@hotmail.com Biomechanics is... The science of mechanical forces on living organisms The forces can be inside or outside the body Biomechanics brought you here today Biomechanics was a controversial subject pre-1920 (wo)man as machine dehumanization 1
6 Things you need to know 1. Force should be applied in the proper direction (technique) 2. Apply force over the greatest range of motion (flexibility) 3. Apply force with proper body positions (power positions) 4. Move in a slow to fast rhythm (controlled acceleration) 5. Coordinate the summation of forces (core stability, legs to arms, slow to fast, stretch reflex) 6. Track and field is a combination of linear and rotary motions (expressed as dynamic movements) 2 more things... You already know more than you think We will cover 32 concepts this lecture We will now cover three main categories: Applications Basics Laws 2
Part I - Applications Get your facts first, then you can distort them as much as you please. - Mark Twain 1. Forces Neutral (A) Lateral bending (E) Compression (B) Shearing (D) Distraction (C) Torsion (F) Implications? strengthening injury prevention injury cause force application growth implications technique technique v. style 3
2. Anisotrophic Quality of Joints Joints having different strengths in response to loads from different directions. Lateral bending compression distraction 3. Dynamic Stability A form of balance Postures in motion If postures cannot be maintained we have technique breakdown Technique breakdown GRF, force, velocity, acceleration, poor summation of forces, poor coordination, poor performance 4
Dynamic Stability 4. Closed Kinetic Chain A multi-link link system One joint affects the next Injury implications Poor sequencing Standing demo 5
5. Foot Pronation Pronation v. pathologic pronation dorsiflexion, eversion, abduction Multi-axial movement What does this mean? Too much - too soon - too fast Weak Foot Theory Hard Level Floor Theory and now a video clip 6. Ground Reaction Time How quickly foot is on/off the ground Sign of speed coordination and balance clarity of nervous system proper biomechanics 1/100th of a second Brent MacFarlane s quote Fast foot drill 6
7. Power Positions Dynamic postures that allow optimal force application PP can facilitate summation of forces May be at beginning, middle or end of proper technique PP can be identified for: running, jumping, throwing, starting, pushing, kicking, striking 8. Technique v. Style Technique Style addressed at ALL use of imagination to stages of solve a technical problem development -Bompa generally recognized individual s attempt to patterns or ways of rebel against authority doing things (!?) efficient movement style generates questions- legal, safe, effective? biomechanically sound 7
9. Balance and Proprioception The body s attempt to place it self in space This is done through: the inner ear visually joint position sense Please stand... 10. Neuroplasticity Ability of NS to adapt to change Training implications Homunculus Clarity of NS speed d of NS My Left Foot You Tube 8
Neuroplasticity 2.0 Write the word biomechanics 11. Multi-lateral Development Inventory of physical skills run, jump, throw, push, pull, strike, etc. Problem solving ability Injury prevention strategies Body awareness Very important in children import decreases with training age Linear People 9
12. Anatomical Adaptation The body adapts to the stresses placed upon it Joint capsule, ligament strength holding elements Developed from wide range of physical skills Part of multi-lateral development both a tactic and a strategy Invisible training Part II - The Basics Did you know that the use of biomechanics helped legitimize the coaching profession? see Chariots of Fire 10
13. Force Force is a push or a pull Produced by energy expenditure Can be internal - muscle contraction Or external - gravity or friction Force = mass x acceleration BIG mass x acceleration = force mass x BIG acceleration = force Big mass x BIG acceleration = force 14. Velocity Velocity v. speed language problem Speed - how fast something is going Velocity - how fast something is going and in what direction Measured in meters/second, feet/second, radians/second, strides/minute distance per time unit distance/time 11
15. Acceleration A positive change in velocity a speeding up Acceleration = velocity/time Sprinters accelerate from 0m-60m The shot is accelerated through the power position Pole vaulters accelerate to the pit when clearing the bar A coordinated summation of forces leads to acceleration 16. Newton s 2nd Law of Motion The acceleration of an object is directly proportional to the force causing the motion and inversely proportional to the mass of the object. BIG force with small mass = acceleration 12
17. Deceleration A negative change in velocity a slowing down Sprinters decelerate from 60m-100m Shot putters decelerate the free arm (called blocking) to quicken their release Pole vaulters decelerate when the hit the pit 18. Blocking Actions the deceleration of a limb in one direction creates a force in that direction. (it creates lift) This blocking action is seen in: arm action at take-off in HJ/TJ Hand to mouth in the sprints Parallel thigh of swing leg in sprints 13
19. Power Most important quality in sport Power = force x distance/time Combination of velocity and strength remember velocity has direction How fast work can be performed 4 expressions of power: 1M 1.Mass, body or object tfurther in time 2. MBO same distance, less time 3. Larger MBO same distance, same time 4. Any combination of 1-3 20. Concentric Contraction Closing joint angle Accelerating actions Flexion of joint All movement begins with flexion which raises the question what moves first with sprinter? 14
21. Eccentric Contractions Opening joint angles Decelerating actions Joint extension Many muscle injuries happen during eccentric ti phase 22. The Stretch Reflex A more forceful concentric contraction can be produced when preceded by an eccentric stretch Summation of forces Ball throw Great Index Finger Race 15
23. Isometric Contractions Work without movement Stabilizing actions Gluts/adductors Rotator cuff/serratus anterior Demo - adductor coordination 24. Levers Short lever fast lever Long lever slow lever 16
25. Arm Drill Acceleration - deceleration Blocking actions 50 arm sweeps = roughly 100m time Newton s 3rd Law for every action there is an equal and opposite reaction 26. Pawing Actions Backward sweep of leg/foot in running Pull of hamstring YouTube - FloJo 10.49 Activated with supination of foot knee up - toe-up raises arch height makes foot rigid level and now a video clip 17
27. Planes of Motion Sagittal (a) sprinting Coronal (c) jumping jack Glut med in single support Transverse (d) hula hoop body separation in throws 28. Center of Mass/Center of Gravity The point where the body s mass is considered to be concentrated Not necessarily a fixed point Males v. females Drape of PV or HJ 18
Part III - The Laws If it weren t for the last minute a lot of things wouldn t get done. - Michael Traylor 29. Inertia - Newton s 1st Law The resistance of a body to a change in motion A body at rest (or in motion) will tend to stay at rest (or in motion) unless acted upon by another force 19
30. Wolff s Law Bone will remodel according to mechanical stress Dynamic loads trigger remodeling affecting: external shape internal architecture a form of anatomical adaptation 31. Davis s Law Soft tissue models according to imposed demands Stretching elongation Contracture shortening Specific use strengthening in that arc of use A form of anatomical adaptation 20
32. Sherrington s Law......of Reciprocal Innervation When a muscle receives a nerve impulse to contract, its antagonist receives simultaneously an impulse to relax. What if there is a loss of co-ordination? When does this start in humans? An example of neuroplasticity A Quick Workshop... You will have 5 minutes to get your answers down You can work with a partner 21