kinesiology. chapter outline the musculoskeletal system human strength and power sources of...

Kinesiology

Chapter Outline

The musculoskeletal system

Human strength and power

Sources of resistance to muscle contraction

Joint biomechanics: concerns in lifting

Movement analysis and exercise prescription

Muscle Pulling Force Manifested As a Pushing ForceMuscle Pulling Force Manifested As a Pushing Force

Muscle Pulling Force Manifested As a Pulling ForceMuscle Pulling Force Manifested As a Pulling Force

Front View of Adult Male Human Skeleton

Front View of Adult Male Human Skeleton

Rear View of Adult Male Human Skeleton

Rear View of Adult Male Human Skeleton

The Vertebral ColumnThe Vertebral Column

Front View of Adult Male Human Skeletal Musculature

Front View of Adult Male Human Skeletal Musculature

Rear View of Adult Male Human Skeletal Musculature

Rear View of Adult Male Human Skeletal Musculature

A LeverA Lever

A First-Class Lever (The Forearm)A First-Class Lever (The Forearm)

A Second-Class Lever (The Foot)A Second-Class Lever (The Foot)

A Third-Class Lever (The Forearm)A Third-Class Lever (The Forearm)

Lever Systems

• Classified systems of torque• Relative positions of force, resistance, and axis

of rotation vary in the different types or classes of levers

Classes of Levers

1. First Class – The applied force and the resistance are on opposite sides of the fulcrum.

2. Second Class – The resistance is between the applied force and the fulcrum.

3. Third Class – The applied force is between the resistance and the fulcrum.

First Class Lever

fulcrum

applied force

resistance armresistance

force arm

Second Class Lever

fulcrum

resistanceapplied

force

resistance arm

force arm

Third Class Lever

fulcrum

resistance

applied force

resistance arm

force arm

Levers In The Musculo-Skeletal System

• Most are third class levers• This system produces a disadvantage for force

but an advantage for speed of movement

DFA

DRA

FM

R

FRO

Levers In The Musculo-Skeletal System

Most of the musculo-skeletal system consists of third class levers.

The resistance arm is longer than the force arm.

Levers In The Musculo-Skeletal System

A

B

The musculo-skeletal lever systems generally favor speed over strength.

In the time that the muscle insertion moves a given distance (red arrow), the resistance moves a much greater distance (blue arrow).

Levers In The Musculo-Skeletal System

A

B

In other words, the end of a limb is moving at a greater velocity than the attachments of the muscles that produce that movement.

Strength vs. Speed in Skeletal Muscle

• In a muscle contraction acting on a limb the resistance moves through the same angular displacement as the muscle insertion.

• The angular velocity of the muscle insertion (A) is equal to the angular velocity of the load (B)

q

AB

Strength vs. Speed in Skeletal Muscle

DFADRA

FM

R

FRO

If DFA = 3 cm and DRA = 30 cm• The relative speed of the resistance to the muscle insertion = DRA/DFA = (30 cm)/(3 cm)

= 10• This means that the resistance is moving at 10 times the velocity of the muscle

insertion

Levers in the Musculo-Skeletal System

• Not all levers in the musculo-skeletal system are third class.

• When performing toe rises the ankle becomes a second class lever system.

fulcrum

DRA

DFA

R

FM

Most of the skeletal muscles operate at a

considerable mechanical disadvantage. Thus, during

sports and other physical activities, forces in the muscles

and tendons are much higher than those exerted by the

hands or feet on external objects or the ground.

Types of Muscle Contractions

• Isometric– Tension is developed– No movement of the joint

• Isotonic– Constant resistance– Variable speed

• Isokinetic– Constant speed of contraction– Variable resistance

Speed vs. Force Movements

• Speed movements– Joints move in sequence– Walking, running

• Force movements– Joints move simultaneously– Squat, bench press

Linear vs. Angular Velocity

r

qA

A

B

B

If you think you're No. 1, you're never going to reach potential. So each day, we

battle. And each day, it changes.

Lelan Rogers – Syracuse University Lacrosse

Assistant Coach

Mechanical Principles

• Mass• Weight• Inertia• Speed • Velocity• Acceleration

Linear Acceleration (in velocity direction)

• This is the familiar stoplight acceleration along a straight line

• Zero to Sixty-Seven (30 m/s) in 5 seconds:– 30 m/s in 5 seconds means 6 m/s2 (~0.6g)

• Typical car acceleration, normal driving ~0.2g

Curves & Centripetal Forces• Going around a curve smushes you against

window– Understand this as inertia: you want to go

straight your body wants tokeep going straight

but the car is acceleratingtowards the center of the curve

Centripetal Forces

• The car is accelerated toward the center of the curve by a centripetal (center seeking) force

Centripetal Forceon car velocity of car

(and the way you’d rather go)

Introduction• Projectile Motion: Motion through the air without a propulsion

Part 1.Motion of Objects Projected Horizontally

v0

x

y

x

y

x

y

x

y

x

y

x

y

•Motion is accelerated

•Acceleration is constant, and downward

• a = g = -10 m/s2

•The horizontal (x) component of velocity is constant

•The horizontal and vertical motions are independent of each other, but they have a common timeg = -10 m/s2

Trajectory

x = v0 ty = h + ½ g t2

Eliminate time, t

t = x/v0

y = h + ½ g (x/v0)2

y = h + ½ (g/v02) x2

y = ½ (g/v02) x2 + h

y

x

h

Parabola, open down

v01v02 > v01

Changes in Vx

y

x

h

Part 2.Motion of objects projected at an angle

x

y

• Motion is accelerated• Acceleration is constant, and

downward• a = g = -9.81m/s2 • The horizontal (x) component of

velocity is constant• The horizontal and vertical

motions are independent of each other, but they have a common time

a = g =

- 9.81m/s2

Trajectory and Horizontal Range

0

5

10

15

20

25

30

35

0 20 40 60 80

15 deg

30 deg

45 deg

60 deg

75 deg

vi = 25 m/s

Velocity

•Final speed = initial speed (conservation of energy)

•Impact angle = - launch angle (symmetry of parabola)

PROJECTILE MOTION - SUMMARY• Projectile motion is motion with a constant

horizontal velocity combined with a constant vertical acceleration

• The projectile moves along a parabola

• When a weight is held in a static position or when it is

moved at a constant velocity, it exerts constant

resistance, only in the downward direction.

Equilibrium

• However, upward or lateral acceleration of the weight

requires additional force.

Overcoming the effect of gravity

Stability• Center of gravity• Line of gravity• Base of support

Center of Gravity

Anatomical Planes of the Human BodyAnatomical Planes of the Human Body

Muscle Fiber Arrangements Muscle Fiber Arrangements

Resistance training is quite safe compared with

other sports and fitness activities. Prudence can keep

injuries to a minimum. Basic safety principles include

good lifting form, appropriate resistance,

accommodation to injuries, balance, and variety.

Specificity is a major consideration when designing

an exercise program to improve performance in a

particular sport activity. The sport movement must be

analyzed qualitatively or quantitatively to determine the

specific joint movements that contribute to the whole-

body movement. Exercises that use similar joint

movements are then emphasized in the resistance

training program.

Stability

• Base of support (bos)• Center of gravity

(cog)/center of mass • Line of gravity (log)

Equilibrium and Movement

• Body segments moved independently– Mass is redistributed– Changes body’s cog

• As long as the cog is located over the bos the body will remain in equilibrium

Stability• Resistance to movement

– mass– log– bos– Move weight in the direction of the oncoming force

Dynamic Balance

• Constant interaction of forces–Move body in a given direction at a

given speed–Smooth transition of cog from one bos

to the next

Dynamic Balance

Force

• F = m(a)• Any influence that can change the state of

motion of an object• The objective of movement must be

considered

Magnitude of Force• Inertia of object and other resisting forces must be

overcome by enough force for movement to occur• Force must have adequate magnitude to overcome

inertia• Liner movement the closer the force is applied to

the cog the less force needed• Rotational movement the farther the force is

applied to the cog the less force is needed• Objects with a fixed point unless the force is

applied through the point of fixation, the object will rotate

MOM and DADMOM• Maximize• Optimize• Minimize

Muscle Pulling Force Manifested As a Pushing ForceMuscle Pulling Force Manifested As a Pushing Force

Muscle Pulling Force Manifested As a Pulling Force

Angular motion

• Object rotates around an axis• Types

– Turn– Spin – Swing

Athlete’s body

• Predominantly rotational

1. Muscles pull on bones2. Bones rotate at joints

Levers• Simple machines that transmit mechanical

energy• Components of a lever

– Rigid object that rotates around an axis– Applied force– Resistance (opposes force)

• Produce torque – Turning effect– Increased by magnifying force and/or distance

from axis of rotation

2 functions of a lever system

1. Magnify speed and distance2. Magnify force

Can not occur at the same time

Short Lever Arm

Long Lever Arm

Optimize

a. First Class. In a first class lever, the weight to be moved is at one end of the lever, the applied force is at the other end, and the fulcrum (the pivot or turning point) is between the two.

b. Second Class. In a second class lever, the weight to be moved is between the applied force and the fulcrum. This type of lever enables a weight to be moved with less force than would be required without a lever. (Many feel that there are no second class levers in the human body.)

c. Third Class. In a third class lever, the weight to be moved is at one end of the lever, the fulcrum is at the other end, and the applied force is between the weight and the fulcrum. This type of lever provides speed, but a greater amount of force is required for a given weight. This is the most common type of lever in the human body.

First Class LeverThe Forearm

Magnify either force or speed and distance

Second Class LeverThe Foot

Magnify force at the expense of speed and distance

Third Class LeverThe Forearm

Magnify speed and distance at the expense of force.

Predominate the body – most muscles apply great force in order to move light resistances over large distances at great speed.

Human Body LeversMost are long• Distal ends capable of moving rapidly

Body movements• Swift, wide movements• Low force • Tasks involving rapid movement with light objects are easily

performed• Very forceful movements may require an anchoring to secure

a mechanical advantage

Bats, sticks, clubs and racquets

• Increase lever arm length• May increase force applied• Demands more force generated by muscles

Movement of the Body

• Outcome of a system of levers that operate together

• Speed– levers function is sequence– Swinging a bat

• Great force– levers function simultaneously– Squat or bench press

Speed

Force

Inertia

A body in motion will stay in motion a body at rest will stay at rest unless acted on by an outside force

Outside forces include• Gravity• Air resistance• Tuff guys

Acceleration

• Movement response• Depends on

– External force applied– Resistance to movement (inertia)

Formulas

• Distance (d)D=Vt

• Force (F)F=ma

• Work (W)W=Fd or W=mad

• Power (P)P=W/t or P=mad/t or

P=FV

Abbreviations• Distance (d)• Velocity (V)• Force (F)• Mass (m)• Acceleration (a)• Time (t)

Linear Acceleration

• Change in velocity• As V and t, a• Only experienced when force is applied

– When force stops, a new speed is achieved• The direction of acceleration is in the same

direction as the force applied• Acceleration is proportional to force applied

Angular Acceleration

• Rate of change of angular speed or direction• Large change in angular velocity + small amount

of time = large angular acceleration• A lever arm only experiences angular

acceleration when an external torque is applied– Torque stops angular acceleration stops

• Angular acceleration is in the direction of the torque and is proportional to the amount of torque

Constant Velocity• Zero acceleration• Equal and opposing forces are encountered• Forces cancel out no acceleration or

deceleration

Acceleration Caused by Gravity• 9.8m/s2

• A falling object accelerates at the rate of 9.8m/s each second it falls

Acceleration Due to Gravity

Radial Acceleration

• Direction change caused by centripetal force• Mass of object + curve radius + speed +

centripetal force• Aimed along the circular path at any instant• The force responsible for change of direction

– mass, centripetal force needed• Instantaneous direction change as turn

radius

Hammer Throw

Action/Reaction

Every action has an equal and opposite reaction

Linear Motion

mass, resistance to change

Movement of the Human Body

Caused by a body segment exerting force when in contact with a surface

• The reaction of the surface moves the body– sand vs. concrete

• Runner – propelled forward with an equal and opposite force pushed backward against the ground– Surface has sufficient friction (resistance to

slipping)

Torque and Action/Reaction

• Every torque exerted had an equal an opposite torque

• Change in angular momentum must be caused by a force that is equal and opposite

When Action/Reaction is not desired• Controlled• Undesired action must be absorbed

– Energy can not be created or destroyed– Purpose of pads

Performing Actions in a Standing Position

• Counter pressure of the ground

• accuracy of movement• Base of support