収縮

1. Origins, structure, and basic meaning

• Structure: 収縮 (しゅうしゅく) is an event noun for a material or muscle decreasing in length or volume, also used with する.
• Basic usage: 素材が収縮する predicates a material’s own change under cooling, while 筋肉の収縮と弛緩 pairs contraction with relaxation as two phases of movement.

2. Common pitfalls and similar expressions

• Intransitive change and nominal phase
  • 素材が収縮する supplies no separate agent causing a reduction. Likewise, 筋肉の収縮 names an observed phase of change, not a transitive act of shrinking the muscle.