What are striations?

In one line

In bodybuilding contests, striations are the thin, long lines that show on the surface of a competitor's muscles.

What are striations?
Thin lines seen on the muscles
The word 'striations' shows up in bodybuilding contest rules. In English it means lines or stripes. Here is what it refers to on the muscles and how each division treats it.
In one line
Thin, long lines on the surface of the muscles
Striations are thin, long lines that show on the surface of the muscles. The English word 'striation' means a long, thin line or a pattern of lines on the surface of something. Contest rules use it to describe how a competitor's body looks.
Background: muscle fibers
A muscle is a bundle of thin fibers
A muscle is made of long, thin cells, and these cells are called 'muscle fibers'. Several muscle fibers are wrapped in a thin layer and tied into a bundle, and many such bundles together make up one muscle.
Same name, different stripes
The cross-stripes seen only under a microscope
The muscles that move the arms and legs show cross-stripes when greatly magnified under a microscope, which is why they are called 'striated muscle'. The stripes come from protein strands lined up in a regular order inside each muscle fiber, and in English these are also called 'striations'. Because they can only be seen under high magnification, they are not the lines people see on stage with the naked eye.
Where the rules mention them
Divisions that say there should be none
The International Fitness and Bodybuilding Federation (IFBB) rules say that in bikini, wellness, women's physique and men's physique, the body should be free of striations. These divisions look for muscles with shape, but without deep splits between muscles or visible lines.
Where it sits in the rules
In the same sentence as 'too lean'
The IFBB men's physique rules ask for a body that is 'neither excessively muscular nor excessively lean' and free of 'deep muscle separation and/or sharp striations'. The same rules add that the very low body fat seen in bodybuilding is not wanted in this division.
In the bodybuilding division
Definition is valued as muscle quality
In contrast, the IFBB bodybuilding rules look at muscle quality as well as size, and list 'definition' as one part of quality. Definition is how clearly each muscle can be seen as separate through the skin. However, these rules do not use the word 'striations' at all.
A common misunderstanding
Are more visible lines better in every division?
No. The IFBB bikini, wellness and men's physique rules say the body should be free of striations. They also say extreme definition and deeply split muscles should be marked down. In these divisions, a body carved down like a bodybuilder's loses points.
Summary
Thin, long lines on the surface of the muscles
Striations are the thin, long lines that show on the surface of a competitor's muscles. Under IFBB rules for divisions such as bikini, wellness and men's physique, they are something the body should not have. Related terms: conditioning, definition, striated muscle.