Biomechanics Lab

Bones and Muscles as Levers

The study of biomechanics applies concepts of physics to the movement of the body.  While the biomechanical movement of the human body is complex, there are also some simple machines at work.  The movement of the body results from the interaction between bones, muscles, and joints.  Many of these interactions form a simple biological machine known as a lever. 

Levers have four main parts:

• The Lever Arm – a movable rod or bar that pivots on the fulcrum
• The Fulcrum (F) – the point at which a lever hinges or pivots

• The Resistance (R) – whatever the lever is being used to move
• The Effort (M) – the force being used to move the resistance

http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/sporting_edge/sci_media/bent_arm/14731-3-eng-NZ/bent_arm_full_size_landscape.jpg

Within the human body, bones are considered the lever arm; the axis of a joint is the fulcrum; resistance is created by the weight of the body part or object being moved or pushed upon; and muscles are considered the effort since they create the actual motion.  For example, raising a glass of water from a table to your mouth is done with a lever.  The radius and ulna act as the lever arm, the elbow joint is the fulcrum, the resistance is the forearm and glass of water, and the effort is created by the biceps muscle.

Joints

A joint is the location where bones meet.  They allow for movement between bones and are a complex arrangement of cartilage, ligaments, tendons, and even fluid.  There are three different types of joint structures depending on the type of tissue between the bones at a joint.

• Cartilaginous – bones at the joint contain cartilage.       
  • Example: joints between the vertebrae
• Fibrous – bones at the joint contain dense fibrous connective tissue.
  • Example – sutures between parts of the skull
• Synovial – bones are not in direct contact, but rather have a cavity or capsule containing synovial fluid. These are the most common types of joints and can be further categorized based on how they move.
  • Figure A summarizes the six types of synovial joints

http://healthpages.org/wp-content/uploads/2012/05/joints-of-body.jpg          

Types of Levers in the Body

First Class Levers – The fulcrum is located between the effort and the resistance.  An example of a first class lever is nodding your head.  The skull acts as the lever arm, the fulcrum is where the skull meets the spine, the resistance is the weight of your head, and your neck muscles provide the effort.

Second Class Levers – The resistance is located between the effort and the fulcrum.  An example of a second class lever is standing on tiptoes.  The foot is the lever arm, the fulcrum is the joints of the toes, the resistance is the weight of the body, and the effort is provided by the muscles of the calf.

Third Class Levers – The effort is located between the resistance and fulcrum.  An example of a third class lever is bending the arm.  The forearm is the lever arm, the fulcrum is the elbow, the resistance is the weight of the forearm, and the effort is provided by the muscles of the biceps.

Usually we test range of motion of the joints as well as strength in the muscles through the joints.  Today, we are only measuring fitness levels using the musclular and skeletal systems.