IPHY 4540 Biomechanics

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• Objective: to learn how to quantitatively analyze the mechanical function of the human musculoskeletal system using principles of physics and physiology.

• Topics:– Functional Anatomy– Tissue Biomechanics (muscle, tendon, bone)– Movement (kinematics)– Movement dynamics (kinetics)

• Whole body, muscle and joint forces• Impulse, Momentum• energy, power• torque

Outline

• Functional Anatomy• Muscle actions• Lever systems in the body

Functional Anatomy

• the study of body components needed to achieve or perform a human movement or functions. – Care about movement produced by muscle group, not

muscle location

Functional Anatomy

Hammill J, Biomechanical Basis of Human Movement

• Terms– superior– Inferior– anterior– posterior– medial– lateral– proximal– distal– superficial– deep– unilateral– ipsilateral– contralateral– bilateral

Functional Anatomy• Reference System

– origin– axes– planes

• Planes– Frontal

• Vertical• Anterior/posterior parts

– Sagittal• Vertical• Left/right parts

– Transverse• Horizontal• Superior/inferior

Functional Anatomy• Reference System

– origin– axes– planes

• Planes– Frontal

• Vertical• Anterior/posterior parts

– Sagittal• Vertical• Left/right parts

– Transverse• Horizontal• Upper/lower

• Axes: – Longitudinal (Twist):

• head to toe

– Mediolateral (Somersault)• Left to right

– Anteroposterior (Cartwheel)• Front to back

The knee

Muscle Actions

• Motors that move our limbs• Example:

– Push-up• Which muscle?• Which joint?• Flexion/extension?

– Leg curl

Muscle Actions

Muscles: - only exert pulling forces- 3 actions: can exert force and

-shorten (shortening/concentric)-stay the same length (isometric)-be lengthened or resist stretching

(lengthening/eccentric)

- when not activated, muscles can be passively lengthened by other forces

Shortening Muscle Actions

Isotonic = constant force (artificial)

Isovelocity = constant velocity (artificial)

Neither, i.e. variable force and velocity (most common)

Isometric Muscle Actions

Muscle produces force, but does not overcome external load, so no movement develops.

Very common: examples?

Lengthening Muscle Actions

Muscles only exert pulling force,

But the opposing force can be greater than the muscle force, forcibly stretching the muscle.

Also very common.High Risk for injuryExamples:

Leg press example

• What is the primary muscle involved?• Describe its actions throughout one cycle.

Muscle Actions

- only exert pulling forces- 3 actions: can exert force and

-shorten (shortening/concentric): force>load-stay the same length (isometric): force=load-be lengthened or resist stretching (lengthening/eccentric)

force<load

Force > load Force = load Force < load

Outline

• Functional Anatomy• Muscle actions• Lever systems in the body

Levers

• A method of transmitting force– Amplify force– Amplify velocity– Amplify movement distance

• Muscles use leverage to generate movement

Levers

• 4 components– Lever (bone)– Fulcrum (pivot point, joint))– Effort force (muscle force)– Load force (external forces)

fulcrum

effort

Levers: The Law

• Law of Levers:– Fload x rload = Feffort x reffort

– r is the distance to the forces

“Give me a lever and I shall move the earth” – Archimedes

Mechanical Advantage: Fload/Feffort > 1, rload < reffort

Mechanical Disadvantage: Fload/Feffort < 1, rload > reffort

Levers: The Law

• Fload rload = Feffort reffort

A vs B: Mechanical Advantage or Disadvantage? Fload/Feffort = ?

rload=1mFeffort=my laptop (2kg)

Levers: 3 classes

Don’t worry about first, second, third classDo understand:fulcrum = joint = pivotThe relative positions of muscle force, joint and

load are important.What is being amplified? Force or velocity

3 classes of levers

Classes of Levers1. 1st Class— see-saw

2. 2nd Class—Wheelbarrow

3. 3rd Class—Tweezers

Levers: Force and Velocity

– Fload x rload = Feffort x reffort

• Class 1– Fload x rload = Feffort x reffort

• If rload>reffort

• Fload< Feffort velocity amplifier

• If rload<reffort

• Fload>Feffort force amplifier

1st Class Levers

Muscle joint load (MJL)

Load joint Muscle (LJM)

1st Class Lever

Muscle joint load

e.g. triceps acting at the elbowVelocity or force magnifier?

1st Class Levers

Muscle joint load

e.g. your head is tilting forward (e.g. sleeping)Muscles on the back of the neck pull

1st Class Levers (MJL) in the body

Amplify velocity of joint extension

1st Class Levers (MJL) tools

Can amplify force or velocity depending on length of the lever

e.g. tool that amps force using 1st class lever

1st Class Levers (MJL) tools

Can amplify force or velocity depending on length of the lever

e.g. tool that amps velocity using 1st class lever

Class 3 levers (JML)

– Fload x rload = Feffort x reffort

• rload>reffort

• Fload< Feffort velocity amplifier

Joint Muscle Load

3rd Class Levers

joint muscle load

3rd Class Levers

joint muscle load

e.g. hold weight in your hand, biceps pulls up

3rd Class Levers (JML) tools

Can only amplify velocity

e.g. field hockey stick, golf putter, shovel

Class 2 levers (JLM)

• rload<reffort

• Fload> Feffort force amplifier

Rare in the body

Jaw joint (using molars) is a good example

Any others?

Joint Load Muscle

2nd Class Levers (JLM) tools

Can only amplify force

e.g. nut cracker

Summary

Classes of Levers1. 1st Class— see-saw, push-up

– Muscle-Joint-Load– Force or Velocity amplifier,

depending on the lever arm

2. 2nd Class—Wheelbarrow– Joint-Load-Muscle– Force Amplifier

1. 3rd Class—Tweezers, biceps-curl – Joint-Muscle-Load– Velocity Amplifier

• Why do we usually see 3rd class levers in the body?

OR• Why do we have short muscle arms?

Anatomical Terms• Joint Position

– To discuss joint position we define joint angle

– joint angle: relative angle between two segments

• Joint Movement– Flexion: relative angle (joint

angle) decreases– Extension: relative angle

increases (straightening movement)

More muscle terms

agonistmuscles creating the same joint movement

antagonistmuscles opposing or producing the opposite joint movementmust relax to allow a movement to occur ORcontract to slow a movement downexample: kicking

co-contraction

1 joint vs. 2 joint muscles

Examples of 1 joint muscles:

Examples of 2 joint (biarticular) muscles:

Biarticular muscles

• Advantages

How do we stand up from a chair?

Joint actions:What muscles act across the hip?What muscles act across the knee?What muscles act across the ankle?All 1-joint muscles? All 2-joint muscles?

IPHY 4540 Biomechanics

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