Wednesday, March 30, 2011

Mechanical Advantage


Most people know that a shorter limbs person able to lift/ carry more weight than a taller guys. I have train with several big guys and manage to follow their training regime and weight. Reason behind it is not because I have super human strength but it is just a mechanical advantage of my body. 

Movement of the body is produce by a system of levers.These series of levers work together to produce coordination action, some by actual movement (dynamic) and other by stabilization (static).

BIOMECHANICS

Axis - Rigid bar that turns about an axis of rotation or a fulcrum

Force - Effort or exertion applied to cause movement against resistance or weight

Resistance - Oppose motive force


Now why does shorter limbs person are best for force training (power lifting) and a taller/ longer limbs person are best suited for speed and range of motion (running/ swimming/etc). All are based on the arm length of the lever.

Resistance Arm - distance between axis and point of resistance application
Force Arm - distance between axis and point of force


The force of an object that is being lift by a subject can be calculate with this formula :

FORCE   x   FORCE ARM   =   RESISTANCE   x   RESISTANCE ARM

Example (1)                                                  
Force x 2cm = 10kg x 9cm                     
             2cm = 90kg                                                                       
                 F = 45kg                                                                        

Change Insertion 1cm
Force x 3cm = 10kg x 9cm   
3cm = 90kg           
F = 30kg                     

Change point of resistance 1cm
Force x 2cm = 10kg x 8cm 
2cm = 80kg
F = 40kg

To simplify all of this, when 2 person that have different length of upper body. One that has a shorter upper body able to do more than 30 or maybe hundreds of reps for incline crunches whereby the other only a numbers due to the effort that need to produce. On the other hand the taller person has more range of motion to complete a set. Don't be surprise when you see a skinny or a person that never workout before who is  short able to lift heavier or may follow your training regime.  

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