What are the different characteristics of isotonic and isometric contractions? What factors determine whether the muscle shortens, lengthens, or stays the same when stimulated? What is the difference between concentric and eccentric contractions?

Explanation:

Isotonic contraction is the contraction of the muscle against resistance in which the length of the muscle changes while Isometric contraction is the contraction of the muscle against resistance in which the length of the muscle remains the same.

In an isotonic contraction, tension develops to a point and then remains constant.

Isotonic contraction can be concentric or eccentric. It is concentric when the muscle shortens and eccentric when the muscle expands.  Examples of activities that involve isotonic contractions include walking, running or lifting a light object.

In an isometric contraction, the muscle does not exceed the load.  Examples of isometric exercises include pushing against a stationary object. Isometric exercises help in building the muscle. Isometric contraction is what happens when we attempt carrying an object that is heavier than us.

The factors determining whether the muscle contracts or elongates vary from the degree of stretch, the strength of stimulation, temperature, the number of cross-bridges formed between actin and myosin, etc.