Simple body machines

Simple body machines It include: 1- Levers. 2- Pullys. 3- Wheel and axle.

Why study a Simple Machine? Simple Machines make work easier by giving the user a mechanical advantage. There are many examples of simple machines inside the body. Simple machines must be well known to determine the level of performance of athletic player. As a result, it will help the biomechanists to improve the players’ performance

Lever System Definition Force Lever is a simple machine, which consists of a rigid bar that can move or rotate around a fixed point or fulcrum when a force is applied to overcome resistance. Resistance Rigid bar Fulcrum

Human equivalents 1- Bone › Rigid bar 2- Joint axis › Fulcrum 3- Muscles › Effort. 4- Resistance › Weight 5- Effort arm › Moment arm of the muscle force 6- Resistance arm › Moment arm of LOG

Effort Arm Resistance Arm Mechanical Advantage (MA) Definition It is the way to measure the efficiency of this machine that means the ability of the machine to magnify force or to increase the output in relation to the input. Mechanical advantage of the lever = Effort Arm Resistance Arm

Effort arm ˃ Resistance arm Effort arm ˂ Resistance arm If MA= 1 Effort arm = Resistance arm The Function: 1. change the direction 2. Balance If MA ˃ 1 Effort arm ˃ Resistance arm The Function: 1. Magnify force If MA ˂ 1 Effort arm ˂ Resistance arm The Function: 1. Magnify speed 2. Range of motion

Classification of Lever 1.First class of lever 2. Second class of lever 3. Third class of lever

1 . First class of lever It is a class of lever at which the fulcrum is located between the point at which the force is applid and the resistance. Crowbar Scissors See-saw Effort Fulcrum Load

MA may be One Greater than one Less than one R R E E R E F F F

Functions of first class of lever Change direction of force Balance of force Magnify force Speed and ROM

At the insertion of the muscle Anatomical examples In axial skeleton: The action of the muscles of the neck against the weight of the head in the upright position The fulcrum Atlanto occipital joint The effort Neck extensor muscles The resistance The weight of the head At the insertion of the muscle POA of Effort POA of Resistance At the segmental COG of the head

In upper limb: The action of the triceps brachii muscle in extending the forearm. The fulcrum Elbow joint The effort Triceps muscle The resistance The weight of the forearm and hand POA of Effort At the insertion of triceps muscle POA of Resistance At the segmental COG of the forearm and hand

At the insertion of muscle In lower limb: The action of the planter flexors muscle during ankle planter flexion in non-weight bearing The fulcrum Ankle joint The effort Plantar flexor muscles The resistance The weight of the foot POA of Effort At the insertion of muscle POA of Resistance At the segmental COG of the foot

Within the human body the action of agonists and antagonist muscle groups is considered first class of lever

2 . Second class of lever It is a class of lever at which the resistance is located between the fulcrum and the effort. Wheel Barrow Nut cracker

The effort arm is always bigger than the resistance arm. EA ˃ RA MA ˃ 1

Functions of second class of lever Magnify force Conserve energy

Anatomical examples In axial skeleton: The action of masseter muscle during eating. The fulcrum Temporomandibular joint The effort Masseter muscle The food when it is located at the posterior aspect of the mouth The resistance POA of Effort At the insertion of masseter muscle POA of Resistance The COG of the food

In upper limb: The action of the brachioradialis muscle during elbow flexion. The fulcrum Elbow joint The effort brachioradialis muscle The resistance The weight of the forearm and hand POA of Effort At the insertion of brachioradialis muscle POA of Resistance At the segmental COG of the forearm and hand

In lower limb: The action of the calf muscle in weight bearing plantar flexion which is called calf raise. The fulcrum The base of the toes. The effort Ankle plantar flexors. The resistance The weight of the body. At the insertion of planter flexors muscle. POA of Effort At the total body COG represented by LOG anterior to ankle joint. POA of Resistance

3 . Third class of lever It is a class of lever at which the effort is located between the fulcrum and the resistance. Shovel Fishing rod

The resistance arm is always bigger than the effort arm. EA ˂ RA MA ˂ 1

Functions of third class of lever Increase ROM Increase speed

Temporomandibular joint At the insertion of masseter muscle Anatomical examples In axial skeleton: The action of masseter muscle when a bite force is applied in the front of mouth The fulcrum Temporomandibular joint The effort Masseter muscle The food when a bite force is applied in the front of mouth. The resistance At the insertion of masseter muscle POA of Effort POA of Resistance The food

In upper limb: The action of the biceps muscle during elbow flexion. The fulcrum Elbow joint The effort biceps muscle The resistance The weight of the forearm and hand POA of Effort At the insertion of biceps muscle POA of Resistance At the segmental COG of the forearm and hand

In lower limb: The action of the quadriceps muscle during knee extension. The fulcrum The knee joint. The effort quadriceps muscle. The resistance The weight of the leg and foot. POA of Effort At the insertion of the quadriceps muscle. At the segmental COG of the leg and foot. POA of Resistance

The class of lever involved in most of sports activities is third one, as these activities require great speed and RON. For example : in tennis players and football players.

For example: Throwing a ball involves levers at shoulder, elbow, & wrist joints The longer the lever, the more effective it is in imparting velocity A tennis player can hit a tennis ball harder with a straight-arm drive than with a bent elbow because the lever (including the racket) is longer & moves at a faster speed

Class of lever in two-joint muscle Definition: Two-joint muscles are muscles, which pass over two joints at the same time. They are also called biarticular muscle. For example Rectus femoris: Second class over the proximal joint (hip joint) Third class over the distal joint (knee joint)

Remember A mechanical advantage less than one doesn’t mean a machine isn’t useful. It just means that instead of multiplying force, the machine multiplies distance. A broom doesn’t push the dust with as much force as you use to push the broom, but a small movement of your arm pushes the dust a large distance.

Solve Sometimes levers are used to multiply distance. For a broom, your upper hand is the fulcrum and your lower hand provides the input force. The mechanical advantage of this broom is: The answer: MA = 0.3 / 1.2 MA = 0.25

Pulley is a simple machine, that performs a mechanical job. Definition Pulley is a simple machine, that performs a mechanical job. It consists of a grooved wheel and a cord or a rope running over it

Types of pulleys 1. Fixed pulley 2. Mobile pulley 3. Mixed pulley

Fixed pulley It is the only example of pulley in human body A fixed pulley changes the direction of a force. Mechanical advantage = 1

mobile pulley It is used in exercises. The mechanical advantage of a mobile pulley is equal to the number of ropes that support the mobile pulley.

Mixed pulley It is used in exercises. The combination between fixed and mobile pulleys. Mixed pulleys acts to increase mechanical advantage. Each additional rope increases mechanical advantage by 1.

Functions of pulleys Change direction of force Balance of force Modify the effect of a force Magnify the force via increasing the MA

1. Wheel: Represented by bony component which can be Human equivalents 1. Wheel: Represented by bony component which can be External bone: as patella Bony prominence: as condyles, trochanters, tuberosities 2. Rope or Cord: is represented by tendon, muscle, musculotendinous junction.

Patella as a pulley Patella acts as an external pulley for the tendon of quadriceps muscle tendon

Patella has the following functions Move the muscle away Increase the moment arm Increase the quadriceps torque Increase the angle of pull Increase the rotatory component Increase the efficiency of quadriceps muscle Improve the mechanical advantage

Lateral malleolus bone as a pulley lateral malleolus acts as a pulley around which tendon of peroneus longus runs. As peroneus longus contracts, it pulls toward it belly (toward the knee). Using the lateral malleolus as a pulley, force is transmitted to plantar aspect of foot resulting in eversion/plantarflexion. Thank you