A peek into the physics of exercises!

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All you fitness aficionados, have you ever wondered, why a push up when done from the knees is easier! Or a triceps dip with bent knees i.e. legs closer to the body is easier than triceps dips where your knees are extended.

As to my daily grind, I always found it easier to open/close a gate or a door from the far end of the hinge, usually, where the handle is placed than to open/close the gate from the near end of the hinge.

So, who do you think is doing that ghost work to make things easy? The same ghost work which made Archimedes say “Give me a place to stand (with my lever) and I can move the Earth”. The LEVERS!

LEVER: A rigid bar that rotates about a fulcrum, used to transmit a force applied at one location in order to move a load/resistance at the other location.  There are 3 classes of levers depending on relative positioning of Fulcrum(Pivot) around which the system moves, the Load or the resistance which you are trying to move, cut, lift etc. and the Effort applied to do the same. The perpendicular distance from the fulcrum to the load is called the load arm/resistance arm, the perpendicular distance from the fulcrum to the point of effort is called the effort arm.

Movements in our body are due to levers. In our human body, Joints being the fulcrum, muscles produce effort to move load, an external weight or body weight. Based on the arrangement of muscles, bones and joints, different classes of lever exist in the body.

First Class Lever: Here the Fulcrum is pivoted in between the effort and the Force. Ex: seesaw.

In our body, it is rare. Example is the joint between the skull and the first vertebrae as a fulcrum of a first class lever. The front and back neck muscles make the effort to move the head (resistance) forward and backward respectively.

 

 

Advantage of first class lever: As shown in the figure, a smaller force can be used to lift heavier loads, provided the load is nearer to the fulcrum.

For ex: In the see-saw, a light weighted kid seated far away from the fulcrum on one side can balance a heavier kid who is seated closer to the fulcrum on the other side.

 

Second Class Lever: Here the load is in between the fulcrum and the effort. Ex: nutcracker.

In our body, while performing heel raises, the joint at the ball of our foot acts as a fulcrum, the body weight is at the center and the calf muscle produces the effort to lift the weight up.

In case of first and second class levers, force is leveraged.

Whereas in the Third class lever, the effort is in between the fulcrum and the load. Ex: chopsticks.

Advantage of Third class levers: They help in magnifying speed and movements. For example while kicking a soccer ball, contractions in the muscle are used to cause a big impact at the end of the leg.

The effort is higher than the load, thus the energy that have to be put is higher than what is needed to just lift the load, but the load moves longer distance in return.

As, Effort (force) x effort arm = Resistance x Resistance arm. Now here in the third class lever, if the effort is higher than the resistance, then the resistance arm would be more, which makes the load move a longer distance.

Thus most of the muscles in our body are third class levers, thus our human body is designed for movement, speed and performance. Therefore for lifting weights our body goes out of its way thus building muscles or strengthening them.

How to identify the lever: Take an exercise, know the muscles used and their insertion point where the muscle’s tendon attaches to the bone, this is the point of effort in most of the exercises. The joint around which the muscle moves is the fulcrum. The load could be body weight or an external weight.

Examples of exercises and levers for third class levers:

Leg extensions – Knee joint is the fulcrum, Quadriceps inserting in the tibia tuberosity is the point of effort and the lower part of the leg is the load. (FER)

Bicep curls – Elbow joint is the fulcrum, biceps insertion into the radius is the effort and the weight carried in the hand is the load. (FER)

Changing Lever length: An important variable to progress or regress an exercise.

When the resistance arm gets longer, the exercise becomes tougher, than the resistance arm being shorter.

For example: Pushups done on knees is easier than done with extended knees in the air. Triceps dips with legs extended is tougher than with shorter legs bent at the knee. A curl-up with arms rested on the thighs is easier than arms rested on the temple than with arms above the head, as in these cases the Resistance is moving far away from the fulcrum.

Now you know to manipulate your exercises by changing those lever lengths!

 

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