Knes Principles of Human Movement

Knes 300 - Principles of Human Movement
Course Objectives 1) Learn about the relationship between mechanical principles and moving bodies. 2) Apply your knowledge of these mechanical principles to well-known skills. Why analyze movement? - Minimize injury, maximize performance, optimize technique.

Knes 300 - Principles of Human Movement
Qualitative vs. Quantitative Approaches Qualitative Description of quality without the use of numbers. Quantitative Involving the use of numbers. Ex. Long jump - “That was a long jump” vs. the jump was 18 feet in length

Qualitative vs. Quantitative Descriptors
good poor long heavy flexed rotated dope tight Quantitative six meters three seconds fifty turns two players ten dollars 45 degrees 55 mph

Qualitative vs. Quantitative Descriptors
Qualitative does not mean ‘general’. A man walking down the street may also be stated ‘a man is walking very slowly, appears to be leaning to the left, and is bearing weight on his right leg for as short a time as possible’. Both Q and Q are important in the biomechanical analysis of human movement and while researchers rely heavily on quantitative techniques, clinicians, coaches, and teachers or physical activities regularly employ qualitative observations of their patients, athletes, or students to formulate opinions or give advise.

Biomechanics The science involving the study of biological systems from a mechanical perspective. Statics and Dynamics are two major sub-branches of mechanics. Statics is the study of systems in a state of constant motion (at rest or constant velocity). Dynamics is the study of systems in which acceleration is present. Kinematics - describes the appearance of motion. Kinetics - the study of forces associated with motion (since F=ma then acceleration is important variable in kinetic analyses).

Chapter 1 - Sport Mechanics
Mechanical Principles Technique Traditional training methods How to use this information

Mechanical Principles Basic rules that govern an athlete’s actions. Ex. - Diver and gravity - optimal flight path - Wrestlers helped by gravity when getting opponent off balance - Ski jumpers using air resistance

Technique - Patterns and sequence of movements that the athletes use to perform a sport skill. - Certain sports include a single skill such as discus throwing while tennis includes forehands, backhands, serves etc. - Each skill has a specific objective that with ‘good’ technique may be achieved with the highest degree of efficiency and success.

Traditional training methods - Many coaches and athletes still follow old, traditional methods in their workouts. - Trial and error methods demonstrate a lack of understanding of mechanical principles. - Copying world champions disregard differences in physique, training and maturity. - Analyze performances and teach movement patterns that produce efficient technique leading to better performances.

How to use this information - Learn to observe, analyze, and correct errors in performance. - Assess the effectiveness of innovations in sport equipment. - Assess training methods for potential safety problems. - Assess the value of innovations in the ways sport skills are performed. - Know what to expect from different body types and different levels of maturity.

Chapter 2 - Starting with Basics
Body weight Mass Inertia Speed, Velocity and Acceleration Gravity Force Vectors Projectiles

Body weight - Newton’s third law states that “For every action there exists an equal AND opposite reaction” - Body’s mass pulls on the earth and the earth’s mass pulls on the body. Scale reading reflects this mutual pulling taking into account the earth’s gravitational pull. The earth’s gravitational pull varies according to location (the further AWAY from the center of the earth, the smaller the gravitational pull - the less you weigh).

Acceleration at Sea Level by Latitude
Location 9.780 Nairobi, Kenya 10 9.782 Caracas Venezuela 20 9.786 Honolulu, Hawaii 30 9.793 Houston, Texas 40 9.802 Denver, Colorado 50 9.811 Bonn, Germany 60 9.819 Anchorage, Alaska

Mass - All objects that have substance or matter have mass. - The human body is composed of bones, muscles, fat, tissues and fluids all of which are substance or matter and have mass. - A heavyweight wrestler has more mass than a gymnast resulting in greater attraction between the earth and the wrestler than between the earth and the gymnast.

Inertia - Resistance to action or to change. - The desired of an object to continue doing whatever it’s doing - even when it’s moving. - All objects want to remain motionless, but if a force moves them, then they want to continue moving in the same direction at a constant speed.

Distance Total ground covered or traveled. A scalar. Displacement As the crow flies - A straight line between the beginning and the end. Measured in cm, m, km. A vector Speed Distance divided by time miles traveled in two hours average 50 mph. Velocity Displacement divided by time. 100 meters south divided by 10 seconds equal 10 meters per second in the south direction.

Speed, Velocity and Acceleration - A sprinter running the 100 m in 10 sec has an average speed of 10 m/s or ~ 22 mph. This average speed indicates that the sprinter must have been going faster and slower at times to average the 22. - Velocity is a more precise description of speed - Giving it direction. Thus it includes both speed and direction - 20 mph due south. - The rate at which velocity changes is termed acceleration. It may be positive or negative.

Gravity - It is constant and it accelerates falling bodies at a rate of 32 feet per second per second or 9.8 meters per second per second. - It affects performance because the effects of gravity change the further you are from the center or core of the earth. - Ex. Mexico vs Moscow distances (elevations and equator).

Center of Gravity - The earth’s gravitational pull on the athlete is concentrated at the athlete’s center of gravity. - It represents the center of how the mass is distributed from head to toes. Muscle and bone are more dense and thus have more mass squashed into the space they occupy and thus the earth pulls more on those parts. - Ex. Males higher cog then females (hips) - Cog changes as limbs move and can be outside the body.

Force - A push or a pull that changes or tends to change the state of motion of an athlete or object. Force vector - refers to when the direction and amount of force is known.

Force Vectors - Addition
+ Tip to Tail = + = Parallelogram

Force Vectors - Subtraction
_ _ = + + = Tip to Tail

Force Vectors - Multiplication
x 2 = + = Tip to Tail

c a b What is a+b+c and 2c-a+3b and –c-b+a and a-b-c and –a-b-c?
How many vectors can you add?

Motion Linear Angular (Rotary) General
Rectilinear (skydiver, putt on level ground) Curvilinear (parabolic trajectory, cannonball) Angular (Rotary) Rotates about an axis (wheels, spin dives, joints, curveballs) General Combination of linear and angular (sprinting)

Projectile Motion To increase the horizontal distance (range) of a projectile you need to consider: The velocity at release The angle at release The height at release

Factors Influencing Projectile Trajectory
Maximum height (m) Range (distance) (m) 5 4 3 2 1 This scaled diagram shows the size and shape of trajectories for an object projected at 10 m/s at different angles.

Newton’s Laws - Law of Inertia - a body will remain at rest or continue to move at a constant velocity unless acted upon by an external force. - Law of Acceleration - the acceleration of an object is directly proportional to the force causing it, it is in the same direction as the force and it is inversely proportional to its mass. - Law of Reaction - for every action there exists an equal and opposite reaction.

Chapter 3 - Getting a Move On
Action - Reaction Momentum Impulse Work Energy Rebound Friction

Action - Reaction This again is referring to Newton’s third law (Law of Reaction). Ex. Sprinter pushing against the blocks and the earth pushing back on the attached block to propel the sprinter forward. The force produced by the sprinter’s muscles overcome inertia and she accelerates. This acceleration is proportional to how much force she applies the the time frame over which it is applied, and it is inversely proportional to her mass.

Momentum A moving athlete/object is an example of mass on the move. Because a certain amount of mass is moving we refer to this as the a/o momentum. It describes the quantity of motion that occurs. To increase momentum the a/o needs to increase either its mass or its velocity or both. Important in sports that have collisions and impact - football, bowling, billiards. Increase mass by putting on muscle to increase power and speed. Car accidents experts reconstruct crash scenes by determining which car had greater momentum.

Momentum Testing the new Armed Forces barriers...
From time to time someone asks what the concrete barriers are in front of controlled and secure buildings. When told that the barriers will stop traffic, even trucks, from approaching the secure building I usually get a look of disbelief. Looking for some footage like this to prove the point, in this test, the following parameters were used. Read them and then watch the film. Truck = 65,000 lbs. Speed = 50 mph Kinetic Energy = 5.5 MILLION ft. lbs. Stopped in 24 INCHES!

Truck Video

Impulse To accelerate or to produce movement, an athlete needs to produce muscular force and create momentum. This force always takes time to produce and we refer to the application of force over a certain amount of time as impulse. Ex. Karate blow - Large force - short period of time. Bones 40 times stronger than concrete. Javelin throw - large force - long period of time. Strength and flexibility are important. High jump - large force - medium period of time. Not a full squat, but a quarter squat and rocking over the heel and backwards lean increase the amount of time over which to produce force.

Conservation of Linear Momentum Total amount of linear momentum of colliding bodies will be the same before and after the collision. If one body gains momentum then the other must lose momentum. Collisions cannot create or dissipate linear momentum but rather transfer it from one object to another. m1v1 + m2v2 = (m1 + m2) (v)

Conservation of Momentum
In the absence of external forces, the total momentum of a given system remains constant. A 90 kg hockey player traveling with a velocity of 6 m/s collides head-on with an 80 kg player traveling a 7 m/s. If the two players entangle and continue traveling together as a unit following the collision, what is their combined velocity? Known: m1= 90 kg m2=80 kg v1= 6 m/s v2= -7 m/s m1v1 + m2v2 = (m1 + m2) (v) (90 kg) (6 m/s) + (80 kg) (-7 m/s) = (90 kg + 80 kg) (v) 540 kg m/s – 560 kg m/s = (170 kg) (v) - 20 kg m/s = (170 kg) (v) v = 0.12 m/s in the direction of the 80 kg player’s original direction of travel

Work Mechanical work defined as force times distance. Ex. Filling shelves, throwing the javelin, ball slowed by turf, lifting weights. Different from physiological work in that for MW the object needs to move. A static or isometric contraction would involve PW but not MW. Unit is the Joule.

Power The rate at which work is done. It may be expressed as P = W/t or P = F x V In the metric system unit for Power is the watt Which is equivalent to 1 joule/second

Energy Defined as the capacity of an a/o to do work. Mechanical energy has three forms. Kinetic, Potential and Strain energy. Kinetic - moving energy KE = ½ * m * v2 Potential - location/position energy PE = m * g * h Strain - stored energy

Conservation of Energy As a diver begins to fall towards water her potential energy is transformed into kinetic energy. A ball thrown into the air has both kinetic and potential energy throughout its flight or parabolic trajectory Ex. Rib cage testing device for crash dummies.

Rebound When objects/bodies separate (move apart) after a collision or impact occurs. Angle of incidence and angle of reflection/rebound measured with respect to the vertical. Coefficient of elasticity/restitution refers to the degree (amount) of recoil/bounce that objects have. The greater the bounce the greater the coefficient (value between 0 and 1) with 0 signifying a completely inelastic object and 1 signifying a completely elastic object.

Angle of Reflection/Rebound
Incidence Rebound

Rebound Affected by temperature and rebounding surface. Heat causes balls to bounce more while artificial turf also will cause a greater bounce.

Friction Force that occurs when an object moves or tends to move while in contact with another object. Reduce - wax skis, curling, bowling lanes Increase - rough gloves, cleats

Mechanical Behavior of Bodies in Contact
What is friction? force acting over the area of contact between two surfaces direction is opposite of motion or motion tendency magnitude is the product of the coefficient of friction () and the normal reaction force (R); F = R

Friction Three types - static, sliding and rolling. Static - seen in resting bodies, resists initiation of movement. Sliding - force that develops when two objects are sliding past each other. Rolling - when round object rolls past another. Factors affecting friction: forces pressing two surfaces together, nature (texture) of surfaces, actual contact area.

Friction Pressure = Force / Area One box exerts greater pressure against the floor than the other, thus squashing the microscopic irregularities found even on the smoothest of surfaces and by so doing it creates the same contact area as the other box.

Static Fm = sR Dynamic Fk = kR Applied external force Friction For static bodies, friction is equal to the applied force. For bodies in motion, friction is constant and less than maximum static friction.

Pushing a desk Pulling a desk R = wt + Pv R = wt - Pv Is it easier to push or pull a desk across a room?

Friction Coefficient of Friction
The ratio of the force needed to overcome the Friction, to the force holding the surface together is called the coefficient of friction The coefficient is an experimentally derived value that depends on the nature of the contact surfaces. The larger the coefficient the more the surfaces cling to each other. A coefficient of 0 would indicate completely frictionless surfaces.

Vectors and Scalars Vectors - Two quantities - Magnitude and Direction
Weight Velocity Displacement Acceleration All forces - friction, drag, lift, buoyancy etc. Scalars - Single quantity - Magnitude mass area distance temperature speed

Formulas Weight = m * g A= v/t PE = m * g * h V= displacement/t
KE = ½ * m * v2 TE = PE + KE + SE A= v/t V= displacement/t Speed = distance/t Impulse = F * t Momentum = m * v Work = F * displacement Power = Work / t

Chapter 4 - Rocking and Rolling
Angular motion Lever Systems Torque Types of levers Angular velocity Inertia, Centripetal and Centrifugal Force Rotary Inertia Angular Momentum

Angular motion Measured in degrees or revolutions, 360 degrees is equal to one full revolution, 180 is half, 90 is one-quarter of a rev. and so on. Also referred to as spin, rotation, twist, swing, etc.

Lever Systems A lever is a simple machine that transmits and changes mechanical energy from one place to another. Always, Read, First Axis, Resistance, Force - What is in the middle will dictate the type of lever system (First, Second or Third Class).

Angular Motion Eccentric Force – force applied a certain distance away from cog of object therefore causing rotation Centric Force – force applied through the center of gravity of object creating linear motion Force couple – two equal and opposite forces that cause rotation

Torque - A rotary, turning, or twisting effect produced by a force acting at a distance from the axis of rotation. The initiation of rotation requires the application of torque. Ex: torque wrench, dumbbell curl. Torque is equal to force multiplied by the length of the force arm (the perpendicular distance between axis and point of force).

Torque A sum of torques may result in no motion (isometric contraction), angular motion (dumbbell curl) or linear motion (rowing boat). The perpendicular distance from where the force is applied to the axis of rotation is termed the torque arm, moment arm and force arm - all meaning the same thing.

Torque video

Types of levers First Class - triceps extension, leg press Second Class - calf raises, rowing Favors the output of force at the expense of speed and range of motion. Third Class - biceps curl Always move the resistance through a larger range of movement than that moved by the force.

Mechanical Advantage It is a measure of the efficiency of a machine or a lever system. In other words what is the machine’s ability to magnify force or another way of expressing it is “what is the output of the machine relative to its input” MA= FA divided by RA (FA/RA)

Mechanical Advantage Note that in third class levers the FA is always less than the RA so MA is less than 1.0, which is low mechanical advantage. Second class levers on the other hand are more efficient with MA greater than 1.0. We make adjustments to increase our mechanical advantage by using a crowbar in prying we increase the FA thus increasing the mechanical advantage or carrying a heavy load close to our bodies to reduce the RA and thus increase the mechanical advantage.

Angular velocity The rate of spin of an athlete or object. The rate of swing of a club or bat. However as the distance from the axis of rotation to the end of the bat increase so does the LINEAR velocity of the end of the bat. Therefore Linear velocity of a rotating segment is the product of the angular velocity and the radius (or distance from axis).

Relationship of Linear and Angular velocities
Lin. Vel = Ang. Vel * radius How fast a ball comes off the bat (lin vel) is equal to how fast you swing (ang vel) the bat times the length of the bat (radius)

Centripetal and Centrifugal Force Centripetal force is that force used to maintain an object moving around a circular path while centrifugal is the equal and opposite reaction to this centripetal force. While this force is affected by both the angular velocity and the mass of the object, it is the angular velocity which has a greater impact.

Rotary Inertia The resistance to rotate or follow a circular path. I = Σ m * r2 Again the a/o wants to remain at rest or continue moving at a constant angular speed. To increase the rotary inertia of an object you increase BOTH the mass of the a/o and how far this mass is from the axis of rotation.

Angular Momentum Much like linear momentum, angular momentum refers to the product of the angular velocity times the rotational inertia of the a/o.

Formulas Angular velocity = Fc = (m * v2)/ r  ang. displ / t
Angular acceleration =  ang. Vel. / t Torque = F * d Angular momentum = Rotary Inertia * ang vel Fc = (m * v2)/ r v is tangential velocity and r is radius of rotation Fc= m * r * ω2 ω = angular velocity T = I * α α = angular acceleration

Chapter 5 - Don’t be a Pushover
Equilibrium, balance and stability Linear stability Rotary stability

Equilibrium or balance implies coordination and control Stability relates to how much resistance a/o put up against having their equilibrium disturbed. The more stable the a/o the more resistance the athlete generates against disruptive forces

Equilibrium, balance and stability Stable Unstable Neutral

Linear stability Defined as the resistance against being moved in a particular direction and resistance against being stopped or having its direction changed once it is moving. While at rest an a/o’s linear stability are govern by its mass and the frictional forces occurring between the a/o and the supporting surfaces. When in motion the a/o’s linear stability is directly related to momentum.

Rotary stability Defined as resistance to being tipped over or upended. Six factors that would increase stability: 1) increase the base of support 2) the a/o’s line of gravity falls within the bos 3) lowering the center of gravity 4) increase body mass 5) base of support extends toward the oncoming force 6) line of gravity shifts toward an oncoming force

Chapter 6 - Going with the Flow
Hydrostatic Pressure Buoyancy Drag Lift

Hydrostatic Pressure Force exerted by a fluid like air or water. Ex. Blankets layered on you, sea level = more blankets of atmosphere - Water is more dense than air thus weighs more, therefore pressure exerted by water increases with depth much faster than in air.

Buoyancy - Acts upward fighting gravity - Pressure increases with depth - Water presses on the athlete from all directions - Push from below (greater pressure) is greater than sides or above - This force from below is called buoyancy - Helium or hot air are also lifted by a buoyant force as a result of being lighter gases than normal air.

Center of Buoyancy - The place where the buoyant force concentrates its upward push on the athlete’s body. - Lungs and torso take up more space and weigh less compared to the legs. - Therefore the c of b is generally just below the rib cage, thus causing a torque which results in a tilted floating position.

To float or not to float that is the question - An a/o in the water has essential two forces acting upon it. Its weight will be pulling it down while the buoyant force will be pulling it up. Depending on which vector is greater - the a/o will float or sink. - Specific gravity is equal to the ratio between the density of the a/o and the density of water. If the spec. grav. is greater than one the a/o will sink, if it is less than one than it will float.

To float or not to float that is the question - Other factors that may affect your ability to float: + gender + age + lung capacity + water temperature and density

Drag Varies according to: Type of fluid (water or air) Density and viscosity of fluid (sticky and clingy) Shape and size of athlete But, most importantly it varies or it is most influenced by the relative velocity of object and fluid.

Drag Three types of drag are surface, form and wave drag. Surface drag is also called viscous drag or skin friction and the amount of surface drag is determined by the relative motion of object and fluid, the area of surface exposed to the flow, the roughness of the object’s surface, and the fluid viscosity.

Drag Form drag is also called shape drag or pressure drag and the amount of form drag is determined by the relative motion of object and fluid, the pressure differential between the leading and trailing edges of the object, and the amount of surface acting at right angles to the flow. Streamlining refers to tapering both front and trailing edges so as to minimize the surface area hitting the flow on the front and the turbulent area on the back.

Drag Wave drag occurs at the interface between water and air. The amount of wave drag is determined by the relative velocity with which the object and wave meet, the surface area of the object acting at right angles to the wave, and the fluid viscosity.

Lift A force that acts perpendicular to the direction of motion. Three ways of developing lift are through an airfoil shaped object, modifying the angle of attack and through spin (lift caused by spinning balls is referred to as the Magnus Effect).

Lift and Magnus Effect A spinning object traveling through the air builds up high pressure on the side spinning into the airflow. Low pressure occurs on the side spinning with the airflow. The ball is deflected from high pressure to low pressure.

Chapter 7 - Analyzing Sport Skills
Objectives Special Characteristics Elite performances Divide into phases Divide into key elements Mechanical reasons

Determine the Objectives of the Skill - Rules of the sport Ex. Throwing the discus for distance and also for accuracy (land on selected sector) - speed of release, spin created, trajectory, stability to avoid foul. Volleyball - jump, spike, ball trajectory, touch net. Wt. Lifting - strength, balance, stability. - Be aware of ALL objectives required for the skill.

Special Characteristics Sport skills can be divided into different types based on a) manner and b) condition. A) Manner - skill performed once (nonrepetitive or discrete) or repeat sequentially (repetitive or cyclic). B) Condition - Predictable environment (closed skills) no need to make quick decisions because of sudden change Clean and jerk, synchronized swimming - easier practice Unpredictable environment (open skills) - presence of opposition or env. Cond. (wind, waves, rain, sun or field) Teach it by making it predictable and repetitive first, then add the opposition.

Study Top-Flight Performances of the Skill - Getting a picture of speed, rhythm, power, body positions, etc. - Tape it from various angles and watch it in slow motion. - Although body types differ, many common features exist. Ex. Golfers shifting their weight and rotating their hips

Divide the skill into phases - Makes your job of looking for errors easier. Not confused by watching too much at the same time. - Four common phases are: Preparatory, Wind-up, Force and Follow-through. Prep - early mistakes will manifest themselves in the resultant outcome. Wind-up - muscle stretch, force over a long distance and time Force - apply it in the right sequence and for the rt amt of time Follow-through - maintain balance and continuity of motion.

Divide into key elements Once you’ve divided the skill into important phases, you can direct your attention towards dividing each phase into key elements. A key element are distinct actions that are essential to the success of each phase in the skill. Key elements are essential in good technique and contribute mechanically toward the success of the skill.

Mechanical reasons By far the most important step in analyzing a skill. This is what differentiates you from a coach that has learned his trade simply from being involved in the sport. Mechanics after all are the foundation of all sport techniques. These techniques are founded on mechanical principles/laws. Thus after choosing the key elements it is important to understand the mechanical purposes behind each element.

Elite Idiosyncrasies Look for basic techniques that top athletes use. As you improve your analytical skill you will begin to disregard some actions elite athletes use that are personal idiosyncrasies and have no mechanical value (ie - Jordan sticking his tongue out!) Remember to take into account maturity, strength, flexibility, and endurance of a young immature athlete or novice.

Chapter 8 - Identifying and Correcting Errors
Observe complete skill Analyze each phase and its key element Use sport mechanics in your analysis Select errors to be corrected Decide on appropriate methods

Observe complete skill Observe and video record your athlete performing the skill from different positions. Front, back, 90 degrees, left and right. Elements that are hidden from one point of view may be clear and unobstructed from another. Be careful if/when filming from the front - SAFETY comes first!! Choose a site with no or little distractions to you or your athlete, this way your athlete can concentrate on the skill. Make certain the athlete appears as large as possible within the field of view of the camera without cutting off any of the action.

Observe complete skill Make certain your athlete has a proper warm-up prior to executing the skill forcefully or maximally. This will allow you to observe the athlete’s performance and get an overall impression. Keep the athlete enthuse by giving some positive feedback but refrain from offering instruction after or during each trial. Your athlete should not strive to impress you but rather give you a true measure of his/her performance. Use visual and auditory signals to gage the quality of the performance (loud foot slap on trip jump, or bad v-ball set.

Analyze each phase and its key elements Start with the result - lack of spiral or distance on a punt. Observe each phase of the skill in sequence Critically observe the first phase (preparation), then shift your attention to the second phase (acceleration) and finish with the follow-through.

Use sport mechanics in your analysis Ask yourself these questions: Does your athlete have optimal stability when applying or receiving force? Is your athlete using all the muscles that make a contribution to the skill? Is your athlete applying force with the muscles in the correct sequence? Is your athlete applying the right amount of muscular force over the appropriate time frame?

Use sport mechanics in your analysis Ask yourself these questions: Is your athlete applying force in the correct direction? Is your athlete correctly applying torque and momentum transfer? Is your athlete decreasing rotary resistance to spin faster and increasing rotary resistance to spin slower?

Select errors to be corrected After analyzing each phase and the key elements associated with each phase, find errors to correct. Rank each error in accordance to its importance.

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