What principle states that a muscle fiber is either producing maximum tension or none at all?

The principle that states a muscle fiber is either producing maximum tension or none at all is known as the all-or-none principle. This concept is fundamental in understanding muscle physiology. When a muscle fiber is stimulated by a sufficient electrical signal, it will contract with maximum force; however, if the stimulus does not reach that threshold, the muscle fiber will not contract at all. This behavior ensures that muscle contractions are efficient and all muscle fibers within a motor unit respond uniformly to stimulation.

In terms of muscle function, the all-or-none principle helps ensure that when a muscle engages, it does so effectively and powerfully, which is crucial for various physical activities. It contrasts with other principles like the sliding filament theory, which explains how muscle contraction occurs at a molecular level, or the length-tension relationship, which describes how the beginning length of the muscle affects its ability to produce force. The force-velocity relationship relates more to how muscle force varies with contraction speed rather than the binary response of muscle fibers.