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?
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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.
Description of quality without the use of numbers.
Involving the use of numbers.
Ex. Long jump - “That was a long jump” vs. the jump was 18 feet in length
55 mphQualitative 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.
Basic rules that govern an athlete’s actions.
- Diver and gravity - optimal flight path
- Wrestlers helped by gravity when getting opponent off balance
- Ski jumpers using air resistance
- 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.
- 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.
- 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.
- 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).
- 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.
- 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.
Total ground covered or traveled. A scalar.
As the crow flies - A straight line between the beginning and the end. Measured in cm, m, km. A vector
Distance divided by time. 100 miles traveled in two hours average 50 mph.
Displacement divided by time. 100 meters south divided by 10 seconds equal 10 meters per second in the south direction.
- 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.
- 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).
- 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.
- 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
Tip to Tail
Tip to Tail
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?
Maximum height (m)
0 1 2 3 4 5 6 7 8 9 10 11
Range (distance) (m)
Factors Influencing Projectile Trajectory
This scaled diagram shows the size and shape of trajectories for an object projected at 10 m/s at different angles.
- 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.
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.
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.
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!
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.
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)
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
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.
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
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
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.
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.
Affected by temperature and rebounding surface. Heat causes balls to bounce more while artificial turf also will cause a greater bounce.
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
What is 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.
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.
Fk = kR
Fm = sR
Applied external force
Mechanical Behavior of Bodies in Contact
For static bodies, friction is equal to the applied force. For bodies in motion, friction is constant and less than maximum static friction.
R = wt + Pv
Pulling a desk
R = wt - Pv
Mechanical Behavior of Bodies in Contact
Is it easier to push or pull a desk across a room?
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 - Two quantities - Magnitude and Direction
All forces - friction, drag, lift, buoyancy etc.
Scalars - Single quantity - Magnitude
speedVectors and Scalars
Speed = distance/t
Impulse = F * t
Momentum = m * v
Work = F * displacement
Power = Work / t
Weight = m * g
PE = m * g * h
KE = ½ * m * v2
TE = PE + KE + SEFormulas
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.
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).
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
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.
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.
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”
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.
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
Angular velocity =
ang. displ / t
Angular acceleration = ang. Vel. / t
Torque = F * d
Angular momentum = Rotary Inertia * ang velFormulas
Stable Unstable Neutral
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.
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
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.
- 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.
- 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.
- 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.
- Other factors that may affect your ability to float:
+ lung capacity
+ water temperature and density
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.
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.
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.
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.
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).
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.
- 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.
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.
- 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
- 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.
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.
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.
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.
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.
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.
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.
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?
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?
After analyzing each phase and the key elements associated with each phase, find errors to correct.
Rank each error in accordance to its importance.