IPHY 4540 Biomechanics
• 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
Hammill J, Biomechanical Basis of Human Movement
Functional Anatomy• Reference System
– origin– axes– planes
• Planes– Frontal
• Vertical• Anterior/posterior parts
– Sagittal• Vertical• Left/right parts
– Transverse• Horizontal• Superior/inferior
Hammill J, Biomechanical Basis of Human Movement
Functional Anatomy• Reference System
– origin– axes– planes
• Planes– Frontal
• Vertical• Anterior/posterior parts
– Sagittal• Vertical• Left/right parts
– Transverse• Horizontal• Upper/lower
Hammill J, Biomechanical Basis of Human Movement
• 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
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)
load
fulcrum
lever
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 = ?
100kg
B
A
F
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
• Class 3– 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)
• Class 2– Fload x rload = Feffort x reffort
• 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)
Hammill J, Biomechanical Basis of Human 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?
