Biomechanics

- Application of mechanical laws to living structures, specifically to the locomoter system of the human body

Application

- Improvement sport technique

- Design of sports equipment

- Prevent injuries

- Analysis of pathology

- Design of prostheses

- Design rehab devices

- Animation for film and video game

- Ergonomics for workplace

Terminology (Midterm exam)

- Qualitative

○ Non-numerical descript of a movement based on Direct observation

§ Coach giving advice

- Quantitative movt analysis

○ A movt is analyzed numerically based on measurements from data collected during the performance of the movt

§ Base from researches

Mass

- Quantity of matter contained in an object, Unit Kg

Force

- Mass*acceleration, Unit Newtons (N) = 1kg/1m/s^2

Weight

- Amount of gravitation force exerted on a body

- Weight = mass*acceleration due to gravity

- Unit is Newtons

Volume

- Amount of space a body occupies

Pressure

- Force distribute over a given area

- Force/Area United N/m^2

Compression

- Pressing or squeezing force directly axially through a body

Tension

- Pulling or stretching force

Shear

- Force directed parallel to a surface

Mechanical Stress

- Similar to pressure, F/A

Lifting a heavy object

- Ask someone to help

- Stand and face object, feet flat, shoulder width and point straight, stable base of support

- Face object in direction you want to move it. Avoid twisting

- Keep object close to body to minimize torque on lower back

- Get a good grip on the object

- Bend at the knees and hips, feel back as straight as possible

- Lift object using knee and hip extensor muscles

- Carry object close to center of gravity

Why a flat back posture

- Minimize L5/S1 disc compressive force and ligament strain

Avoid full flexion of trunk, lower shear load on back. Probability of disc herniation is increase by repeated/prolongs full flexion of trunk

Stand for a brief period of time before lifting something. Will prepare disc and passive tissue to reduce injury

Contract core muscles to add vertebral column. Reduce both the forces required

Avoid lifting or spine bending after rising from bed.

Levels of the human body

Lever

- A rigid bar that turns about an axis

- Bones represent the bars and joint are the axes

- Contraction of muscle provides the force to move the levers

Force point

- First point of level

- Exact point where effort is applied, Muscle insertion

Resistance point

- Exact point where resistance acts, segment plus external weight

Fulcrum

- The axis of motion

Force arm

- Perpendicular distance from the fulcrum to the axis of rotation

Resistance arm

- Perpendicular distance from fulcrum to

First class, second class, third class level

- 3 types of levers based where fulcrum is

First class

- A seesaw

- Fulcrum is located between he force point and resistance point

- E.x Triceps

- Can have MA =1, .1, ,1

- Depends where fulcrum is located, in middle, closer to force point or close to resistance point

Second class

- Resistance point between force point and fulcrum

- E.x Wheel barrow

- MA>1, always force lever

Third Class

- Force point is at some point between the resistant point and fulcrum

- E.x Bicep

- Permitted muscle to be inserted at join and pull lever up

- MA,1, always a speed level

Mechanical advantage

- Ratio of force arm length to resistance arm length

- Force arm/resistance arm

- Higher the ratio, easier it is to lift

Force lever

- Force arm is longer than resistance, lever is called force level

- Requires half amount of force to lift a 100N object

- M.A is more than 1

Speed level

- Resistance arm is longer than the force arm

- We can move it fast and more range of motion

- Need more force to lift 100N object

- M.A is less than 1

Moment arm

- Perpendicular distance between the force's line of action and axis of rotation

- Fa and Fb like in physics

- Longer wrench, longer moment arm provide less force

Torque

- Product of force and the moment arms from the force's line of action to the axis of rotation

- Rotary force

Keep weight close to you, closer to centre of gravity, easier itll be

Centre of Gravity

Imaginary point in the centre where weight of body is balanced

- Point where body can freely move around

- Between transverse, frontal and sagittal

- Point where weight is equal on all opposite sides

Location depends on the body proportions and anatomical positions

Taller people have higher CG

Slightly higher in males than females

Influenced by changing body positions and limb positions

Addition of external weight like a backpack relocated the CG.

Why is it useful

Used to describe the movement of the body through space

Important for stability

Factor to Calculate amount of work

How to locate it

Reaction board method

- Used for a static position of human body

- Assume that CG is the fulcrum and apply the Principle of Levers, lie on board and balance either end

Segmental Method

- Used for locating CG of a body in motion

Balance

- Defined as the ability control equilibrium

Stability

- Firmness of balance

- Can be increased by:

○ Increase body mass

○ Increase bass of support

○ Increase friction between body and surface contacted

○ Vertically positioning the CG as low as possible

○ Horizontally positioning the CG near the edge of the base of support towards the oncoming external force

For balanced to be maintained in any stationary position

- CG must remain over base of support, if CG passes outside the base of support the body is off balance in that direction

- Heavy objects carried close to body's CG, less likelihood of a loss of balance

Increase stability by

- Increase body mass

- Increase base of support (stance)

- Increase friction

Think of sumo wrestler

- Big mass, big stance

Newtons law of motion

- First law

○ Inertia: body will maintain in a state of rest or constant velocity unless acted by an external force

○ Amount of inertia is proportional to its mass

- Second law

○ Law of Acceleration

§ Force = mass*acceleration

- Third Law

○ Equal and opposite reaction

Momentum

- Mass*velocity

- Quantity of motion as object is in motion

Work vs Power

Work

Force * distance = Nm = 1.0 joule

Power

Work per unit of time

Force*distance/time

Force*velocity

Watts (joule per second)

Walking vs running

Running

- both feet are off the ground, running as a series of jumps

- No time when both feet are on the ground

- Stance phase is much shorter (one foot on the ground)

Walking

- Both feet on the ground

Double support when both feet are on the ground

Stance is foot t are on the ground

Swing is when the leg isn't touching the ground

Running speed

Stride length*stride rate

Length is dependent of leg length and power of the stride

Leg speed is depend on rate of muscle contractions and skill in running

Running mechanism vary from person

Slow running speeds, complete contract is used

As speed increase, amount of foot contract lessen

At slow running speeds, runner is more erect

At full speed, a spring learns forward about 15 degrees from perpendicular

Left leg stance, right leg swing

Both can't be swing