LEVERS AND PULLEYS IN HUMAN BODY HARSH RAI ( ) BPT 2 nd YEAR

LEVER SYSTEMS A lever is any rigid system that rotates around a fulcrum. This system is used to assess the relative torques of internal and external forces. Parts of a lever :- fulcrum, load/resistance and effort. Types of levers:- 1)First class lever (Lever of power and speed) The fulcrum is in between resistance and effort. Torque = force x moment arm (MA)

MECHANICAAL ADVANTAGE It is the measure of mechanical efficiency of lever. M Ad = EA RA If this ratio is more than 1 there is a mechanical advantage and even the small effort force can result into greater torque and win over the resistance force. If this ratio is less than 1 there is a mechanical disadvantage and the lever is said to be “mechanically insufficient” because the magnitude of the effort force must be always greater than the magnitude of the resistance force for the torque of the effort force to win. For example:-

2) Second class lever (lever of power) Resistance is in between fulcrum and effort. EA > RA ( M Ad > 1 ) This type of lever is meant for power because it is always at mechanical advantage. 3) Third class lever (lever of speed) Effort is in between fulcrum and resistance. EA < RA (M Ad< 1 ) This class of lever is meant for speed because it is always at mechanical disadvantage.

Examples of levers in human body:- Among these first and second class levers are rare in human body and the third class levers are most common. To apply the concept of lever to bones in body we have to consider the joint axis fixed (as there is always a little translatory motion with rotatory motion and the joint axis shifts continuously). FIRST CLASS LEVERS

SECOND CLASS LEVERS

THIRD CLASS LEVER

ANATOMICAL PULLEY The fibers of a muscle or a muscles tendon wrap around a bone or are deflected by a bony prominence and due to that pull of muscle is altered (line of force of muscle), then the bone and bony prominence causing the deflection forms an anatomical pulley. Pulleys change the direction of force without changing the magnitude which makes the task easier. They do so by deflecting the action line of the muscle farther from the joint axis thus increasing the moment arm of the muscle force. By increasing moment arm of a muscle force same muscle will produce greater torque because:- TORQUE = FORCE X MOMENT ARM Examples of anatomical pulley in human body are:- 1) patella (sesmoid bone) 2) humeral head, medial and lateral tubercles for deltoid at shoulder. 3)lateral malleolus act as pulley for fibularis longus muscle in knee.

Anatomical pulley at shoulder joint. Line of pull

ANATOMICAL PULLEY AT KNEE JOINT

THANK YOU REFRENCES:-  1) JIONT STRUCTURE AND FUNCTION (by Pamela K. Levangie, C. Norkin, D. Lewek)  2) Exercise therapy (by Dena Gardner)