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 Planes origin axes planes Frontal Vertical Anterior/posterior parts Sagittal Left/right parts Transverse Horizontal Superior/inferior Hammill J, Biomechanical Basis of Human Movement

Functional Anatomy Reference System Planes origin axes planes Frontal Vertical Anterior/posterior parts Sagittal Left/right parts Transverse Horizontal Upper/lower Hammill J, Biomechanical Basis of Human Movement

Axes: Longitudinal (Twist): Mediolateral (Somersault) 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 Leg curl 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 injury Examples:

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) effort load lever fulcrum

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 F A rload=1m Feffort=my laptop (2kg) B

Levers: 3 classes Don’t worry about first, second, third class Do understand: fulcrum = joint = pivot The relative positions of muscle force, joint and load are important. What is being amplified? Force or velocity

3 classes of levers Classes of Levers 1st Class— see-saw 2nd Class—Wheelbarrow 3rd Class—Tweezers

Levers: Force and Velocity Fload x rload = Feffort x reffort Class 1 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 elbow Velocity 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) 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 Rare in the body 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 Nutcracker, wheelbarrow, chef’s knife

Summary Classes of Levers 1st Class— see-saw, push-up Muscle-Joint-Load Force or Velocity amplifier, depending on the lever arm 2nd Class—Wheelbarrow Joint-Load-Muscle Force Amplifier 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 Joint Movement 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 agonist muscles creating the same joint movement antagonist muscles opposing or producing the opposite joint movement must relax to allow a movement to occur OR contract to slow a movement down example: 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?