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Define and explain the difference between isotonic and isometric contraction and give an example of a specific movement for each. What is the apparent contradiction in the term isometric contraction? How is this type of contraction possible?

Isotonic means same tension, that is, a phase of muscle contraction that involves movement with a constant tension or force. An example is what the biceps brachii muscle does when flexing the elbow—once tension increases enough to move the weight of the forearm, the forearm moves steadily without further increase in tension. Isometric means same length, that is, a phase of muscle contraction that involves development of force without the muscle actually shortening and moving a load. An example is what the biceps brachii muscle does when pulling on a load too heavy to move—tension increases to the maximum that muscle can produce, but the muscle does not shorten because the load is too heavy to be moved. The contradiction is that contraction means shortening, yet shortening does not occur. Isometric contraction occurs because of series elastic elements that stretch slightly as the sarcomeres contract slightly, but overall muscle length does not change significantly.