Introduction to

Biomechanics

The Musculo-skeletal SystemMuscular System• Almost ½ the body’s weight is muscle• There are more than 640 muscles in the

body• Muscles can shorten and pull but not push• Most muscles are arranged in opposing

teams e.g. agonistic/antagonistic - as each team pulls, the other team relaxes and gets stretched

The Musculo-skeletal SystemSkeletal SystemThe skeleton has 3 major roles1. It protects vitals organs2. It provides body shape3. It allows us to move as our muscles are

attached to our bones – when our muscles move – our bones move to.

Skeletal SystemSkeletal System Factoids• You are born with 350 bones but

only have 206 bones as an adult – some bones fuse together to form one bone

Bone Structure• A typical bone has a strong outer layer

of compact bone• Inside is a layer of flexible spongy bone

which looks like honeycomb• The middle of some bones consist of a

jelly-like substance called bone marrow which is where new red blood cells are produced

Bone Structure

Naming Skeletal Muscles:Location – e.g. intercostalsShape of Muscles – e.g. Deltoid – triangleSize – e.g. Longus, maximusDirection of muscle fibres – e.g.

transverse, obliqueNumber of muscle parts e.g. quadriceps

Biomechanics• The study of mechanics in the human body• Divided into 2 areas1. Kinetics – the forces producing motion e.g.

muscles, gravity2. Kinematics – the description of motion e.g.

type, location, direction, planes of movement

Biomechanics• The human skeleton is a system of

levers• Muscle force moves the skeleton3 types of levers in the body1. Class 12. Class 23. Class 3

Class 1 Levers

Class 2 Levers

Class 3 Levers

Note the contact point

The Lever Arm

Moments or Torque

Mechanical Disadvantage

Effort and Angles

Forces in Your Body• When you walk, there is 2 to 3 times your

body weight transmitted through each foot.• When you run, this is 7 to 8 times• The foot has 26 bones – everything must be

functioning correctly to avoid injury• E.g. flat feet Click here to view a graphical representation of flat feet (online)

Forces in Your Body• When you sit with bad posture, there is a

200% increase pressure in your spine.• Reaching for your toes is a 300% increase• Human movement is very complex. There

may be dozens of joints and muscles working to achieve a desired movement.

Biomechanics in Physiotherapy• It is essential to have a thorough

knowledge of what is “normal” for the human body.

• i.e. knowing the resultant action if a muscle contracts

• i.e. knowing the possible result of a muscle not functioning correctly