1. 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

2. Outline
Functional Anatomy
Muscle actions
Lever systems in the body

3. 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

4. Functional Anatomy
Hammill J, Biomechanical Basis of Human Movement

5. Terms superior Inferior anterior posterior medial lateral proximal
distal
superficial
deep
unilateral
ipsilateral
contralateral
bilateral
Hammill J, Biomechanical Basis of Human Movement

6. 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

7. 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

8. Axes: Longitudinal (Twist): Mediolateral (Somersault)
head to toe
Mediolateral (Somersault)
Left to right
Anteroposterior (Cartwheel)
Front to back

9. The knee

10. Muscle Actions Motors that move our limbs Example: Push-up Leg curl
Which muscle?
Which joint?
Flexion/extension?
Leg curl

11. 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

12. Shortening Muscle Actions
Isotonic = constant force (artificial)
Isovelocity = constant velocity (artificial)
Neither, i.e. variable force and velocity (most common)

13. Isometric Muscle Actions
Muscle produces force, but does not overcome external load, so no movement develops.
Very common: examples?

14. 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:

15. Leg press example What is the primary muscle involved?
Describe its actions throughout one cycle.

17. 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

18. Outline
Functional Anatomy
Muscle actions
Lever systems in the body

19. Levers A method of transmitting force
Amplify force
Amplify velocity
Amplify movement distance
Muscles use leverage to generate movement

20. Levers 4 components Lever (bone) Fulcrum (pivot point, joint))
Effort force (muscle force)
Load force (external forces)
effort
load
lever
fulcrum

21. 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

22. 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

23. 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

24. 3 classes of levers Classes of Levers 1st Class— see-saw
2nd Class—Wheelbarrow
3rd Class—Tweezers

25. 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

26. 1st Class Levers
Muscle joint load (MJL)
Load joint Muscle (LJM)

27. 1st Class Lever Muscle joint load e.g. triceps acting at the elbow
Velocity or force magnifier?

28. 1st Class Levers Muscle joint load
e.g. your head is tilting forward (e.g. sleeping)
Muscles on the back of the neck pull

29. 1st Class Levers (MJL) in the body
Amplify velocity of joint extension

30. 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

31. 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

32. Class 3 levers (JML) Class 3 Fload x rload = Feffort x reffort
rload>reffort
Fload< Feffort velocity amplifier
Joint Muscle Load

33. 3rd Class Levers
joint muscle load

34. 3rd Class Levers joint muscle load
e.g. hold weight in your hand, biceps pulls up

35. 3rd Class Levers (JML) tools
Can only amplify velocity
e.g. field hockey stick, golf putter, shovel

36. 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

37. 2nd Class Levers (JLM) tools
Can only amplify force
e.g. nut cracker
Nutcracker, wheelbarrow, chef’s knife

38. 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

39. Why do we usually see 3rd class levers in the body?OR
Why do we have short muscle arms?

40. 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

41. 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

42. 1 joint vs. 2 joint muscles Examples of 1 joint muscles:
Examples of 2 joint (biarticular) muscles:

43. Biarticular muscles
Advantages

44. 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?