Muscle contractions occur when your brain signals to your body to move a muscle or keep a muscle in a certain position. Two muscle contraction types are isometric and isotonic muscle contractions. Each muscle contraction type can help you to build muscle over time, but involves different actions to accomplish this.
Isotonic Significance
An isotonic muscle contraction involves a change in your muscle's length and an increase in muscle tension. Place your left hand on your right bicep with your right arm extended. Now pull the right hand in toward your shoulder. You should feel the length of your bicep muscle get shorter, illustrating how a muscle's length can change. Isotonic contractions involve either muscle lengthening or shortening, coupled with an increase in muscle tension -- an example is lifting an object off a table. Your biceps muscles shorten to lift the object and there is tension in the muscles because you are supporting the weight of the item.
Isometric Significance
An isometric contraction is one where your muscle length does not change, nor does the resistance against your muscles. An example is leaning on a wall. The wall will not move, therefore your muscles will not move. What can increase, however, is your muscle tension. You can push very hard against the wall to increase your muscle contraction. This can build your muscles in a different manner than standard isotonic contractions like a bicep curl or shoulder press.
Exercise Examples
Isotonic and isometric contractions can serve as the push-and-pulls that guide you through your everyday life. When you are sitting still, unbeknown to you, your spinal stabilizing muscles are pushing against your spine, which helps you to sit straight and upright. If you move your body, however, to scratch your head or turn a page in a book, this is an example of an isotonic contraction.
Differences
An isotonic contraction differs from an isometric contraction because an isotonic contraction involves change in muscle length. An isometric contraction does not mean the muscle length changes. Also, an isotonic contraction will eventually become muscle shortening. Holding an object constant for a period of time will inevitably cause your muscles to fail, which will shorten the muscle. Isotonic contractions are more common than isometric. Your muscles lengthen and shorten all day: when you walk, when you stand, etc. However, you are likely to spend less time pushing against a door, which would be an isometric contraction.
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