Biology Question #2001

Angie, a 19 year old female from New Tripoli, PA asks on March 22, 2004,

What goes on during the change between isometric and isotonic in muscle cells? What does it look like?

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The answer

Michael Poling answered on March 23, 2004

Isometric and isotonic are types of contractions of muscles. Muscles are made of a bunch of fibres, which all run parallel to each other. They only connect when our nerves tell them to...otherwise they kind of float, one on top of the other. When the nerves from our brain tell them to connect, the fibres link up with one another with and pull along, shortening the muscle. An ISOTONIC contraction is where the tension on the muscle fibres is equal all the way through a movement. Imagine if you hold onto the end of a rope and pull a weight on the other end. If you didn't take up the slack after pulling, the rope wouldn't be tight enough to pull again. An Isotonic contraction would be like moving backward with the end of the rope, keeping it tight.

An ISOMETRIC contraction is when the length of the muscle doesn't change. In other words, the fibres don't move (and neither does the joint). This would be like you pulling on one end of the rope and someone else pulling equally on the other end (a tug o' war). No one moves because you are both equally as strong.

For more information and a picture of how this works check out Penn State University's muscle page.

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