Muscle/MuscleMechanics/IsometricIsotonicTwitches

POINT!

In an isometric contraction the muscle produces force and does not shorten. In an isotonic contraction the muscle shortens and lifts a load (it performs work).

Isometric and Isotonic Twitch Contractions

The “pure” definition of an isometric contraction is based on studies made on isolated muscles. The above figure shows the force and length changes over time when in an isometric contraction. The muscle is clamped at both ends by its tendons, therefore the action of the myofilaments during contraction generate force that is transmitted into the tendon. This force is then recorded as shown above.

In your body it is rare for a muscle to contract isometrically. An example would be stretching your arms out underneath a car and trying to lift it. Your biceps would produce force but would not be able to shorten as you couldn’t shift the car.

An isotonic contraction is when the muscle shortens while lifting a load, doing work. In order to lift the load, the muscle must first develop enough force to oppose that produced by the load. Once this force is produced any excess myofilament interaction is utilized to shorten the muscle and lift the load. As the muscle shortens the force remains constant, hence the term isotonic (same force).

Most contractions in your body are isotonic. For example when you lift up a cup to drink your biceps shortens as you move the cup to your mouth, pulling your forearm towards you.

Challenge Quiz

You must wait for the CORRECT! 正確!

<GIFT> //LEVEL:2 //RAND In an {=isometric~isotonic} contraction the muscle produces force without shortening.

//LEVEL:2 //RAND The force produced in an isometric contraction is transmitted through the tendon. {=True~False}

//LEVEL:2 //RAND In an {isometric~=isotonic} contraction the muscle shortens while lifting a load.

//LEVEL:2 //RAND The muscles in your body are most likely to perform {isometric~=isotonic} contractions.

//LEVEL:2 //RAND The term isotonic means {same length~=same force}.

//LEVEL:2 //RAND The term isometric means {=same length~same force}.