Question about technique related terminology

[Karelipoeg]

Hi,

I thought I knew it, but recently I i got a little confused.

Three terms:
Contraction, Extension, Flexion.

1) Contraction seems obvious. When you contract your muscles (for example lower back), the muscles become shorter in the process, thus creating a back arch.
2) Extension, according to my understanding, should be the opposite then. You extend your muscles, making them longer, pulling them apart, creating a rounded back. But in this case, why are back extensions called back extensions, instead of back contractions? Because you contract your back muscles in the process. Is it named by the bottom of the movement (performed on back extension bench or glute-ham bench), when your back is extended?
3) Flexion. I have come across situations where people say that back extension and back flexion are opposite. In this case, flexion would be equal to contraction. But what is confusing, is that when doing flexibility exercises, you want to become more flexible, you flex your muscles, pulling them apart, making them longer, extending them, isn't that so? What is back flexion, is it arching your back or rounding your back?
So flexing your muscles (you flex your biceps), are you contraction them or extending them?

[Satch12879]

No, you contract muscles to flex or extend joints.

Muscles can only contract, or get shorter, yes.

Joints either extend, moving attached segments away from some axis on the body, or flex, move them toward the body.

In the case of the elbow joint, the contraction of the biceps causes the joint to flex bringing the forearm closer to the upper arm; the contraction of the triceps causes extension pushing the firearm away.

Similar pairs cause knee extension/flexion and extension/flexion of the various portions of the spine.

[JD Keip]

Flexion and extension have anatomical definitions, see Anatomical terms of motion - Wikipedia

But yeah we use them to describe technique matters.

[Dillon Spencer]

Yeah it's probably most confusing when talking about the spine. Well, I actually find shoulder flexion and extension the hardest to keep straight because the damn things have so many different ways they can move. As far as the spine goes, you contract the muscles of the posterior chain to extend the spine, for our purposes to keep it in a rigid natural position under load. You flex the spine when you round it forward, either by actively contracting the abdominal muscles or by relaxing under load.

It's all easier to picture with a hinge joint, like Satch's example of the elbow. Other joints can get a little more confusing.

[Mark Rippetoe]

No, you contract muscles to flex or extend joints.

Muscles can only contract, or get shorter, yes.

Muscle "contraction" occurs when the motor units fire and the force of tension is produced. This action can result in tension being produced when the muscle gets shorter (a "concentric" contraction), in tension being produced when the muscle lengthens (an "eccentric" contraction), or when the muscle generates tension while remaining the same length (an "isometric" contraction). All three are expressions of the activity of the sarcomere. Sarcomere - Wikipedia

The term "contraction" is used by convention to describe all three of these actions, and I agree that it is confusing -- I prefer the term "muscle action" since it does not connote shortening.