1. Chapter 3 Biomechanics Concepts I
Biomechanics: Study of biological systems by means of mechanical principles
Sir Isaac Newton, father of Mechanics

2. Basic types of Motion Linear Angular or rotational Combined or general
rectilinear
curvilinear
Angular or rotational
Combined or general

3. Human Analysis
Internal: mechanical factors creating and controlling movement inside the body
External: factors affecting motion from outside the body

4. Kinematics Describes motion Vectors Angular and linear quantities Time
Position
Displacement
Velocity
Acceleration
Vectors
Angular and linear quantities

5. Kinematics Formulas

6. Kinetics Explains causes of motion Axis Mass
amount of matter (kg)
Inertia: resistance to being moved
Moment of Inertia (rotation) I = m·r2
Axis

7. Kinetics Force: push or pull that tends to produce acceleration
Important factor in injuries
Vector

8. Kinetics Idealized force vector Force couple system d F F’ F M=Fd d d

9. Kinetics: Force Force & Injury factors Magnitude Location Direction
Duration
Frequency
Variability
Rate

10. Kinetics: Force System
Linear
Parallel
Concurrent
General
Force Couple

11. Center of Mass or Gravity
Imaginary point where all the mass of the body or system is concentrated
Point where the body’s mass is equally distributed

12. Pressure P = F/A Units (Pa = N m2)
In the human body also called stress
Important predisposing factor for injuries

13. Moments of Force (Torque)
Effect of a force that tends to cause rotation about an axis
M = F ·d (Nm)
If F and d are 
Force through axis

14. Moments of Force (Torque)
Force components
Rotation
Stabilizing or destabilizing component

15. Moments of Force (Torque)
Net Joint Moment
Sum of the moments acting about an axis
Human: represent the muscular activity at a joint
Concentric action
Eccentric action
Isometric

16. Moments of Force (Torque)
Large moments tends to produce injuries on the musculo-skeletal system
Structural deviation leads to different MA’s

17. 1st Law of Motion
A body a rest or in a uniform (linear or angular) motion will tend to remain at rest or in motion unless acted by an external force or torque
Whiplash injuries

18. 2nd Law of Motion
A force or torque acting on a body will produce an acceleration proportional to the force or torque
F = m ·a or T= I · F

19. 3rd Law of Motion
For every action there is an equal and opposite reaction (torque and/or force)
Contact forces: GRF, other players etc.
GRF

20. Equilibrium Sum of forces and the sum of moments must equal zero
Dynamic Equilibrium
Must follow equations of motions
 F = m x a
 T = I x 

21. Work & Power Mechanical Work Power: rate of work W= F ·d (Joules)
W= F ·d·cos ()
Power: rate of work
P = W/t (Watts)
P = F ·v
P = F ·(d/t) d W

22. Mechanical Energy Capacity or ability to do work
Accounts for most severe injuries
Classified into
Kinetic (motion)
Potential (position or deformation)

23. Kinetic Energy
Body’s motion
Linear or Angular
KE=.5·m·v2
KE=.5 ·I·2

24. Potential Energy
Gravitational: potential to perform work due to the height of the body
Ep= m·g·h
Strain: energy stored due to deformation
Es= .5·k·x2

25. Total Mechanical Energy
Body segment’s: rigid (nodeformable), no strain energy in the system
TME = Sum of KE, KE, PE
TME = (.5·m ·v2)+(.5 ·I ·2)+(m ·g ·h )

26. Momentum P Quantity of motion p=m ·v (linear) Conservation of Momentum
Transfer of Momentum
Injury may result when momentum transferred exceeds the tolerance of the tissue
Impulse = Momentum

27. Angular Momentum Quantity of angular motion H=I · (angular)
Conservation of angular momentum
Transfer of angular momentum

28. Collisions Large impact forces due to short impact time
Elastic deformation
Plastic deformation (permanent change)
Elasticity: ability to return to original shape
Elastoplastic collisions
Some permanent deformation
Transfer and loss of energy & velocity
Coefficient of restitution
e=Rvpost/Rvpre

29. Friction Resistance between two bodies trying to slide
Imperfection of the surfaces
Microscopic irregularities - asperities
Static friction
f< s·N
Kinetic
f=µk·N f N

30. Friction
Rolling: Lower that static and kinetic friction ( times)
Joint Friction - minimized
Blood vessels - atherosclerosis

31. Fluid mechanics
Branch of mechanics dealing with the properties and behaviors of gases & fluids

32. Fluid Flow Laminar Turbulent
Effects of friction on arterial blood flow

33. Fluid Forces Buoyancy Drag Lift Magnus forces Viscosity
Surface
Pressure
Wave
Lift
Magnus forces
Viscosity
Biological tissue must have a fluid component

34. Fluid Forces