腹筋

1. Origins, structure, and basic meaning

• Structure: 腹筋 is read ふっきん and means the abdominal muscles or a sit-up exercise using those muscles.
• Basic usage: With a count, as in 腹筋を十回, it refers to the exercise; when they hurt from laughing, it refers to the muscles.

2. Common pitfalls and similar expressions

• する and 鍛える
  • 腹筋をする means doing sit-ups, while 腹筋を鍛える means strengthening the abdominal muscles. The latter is not limited to one particular exercise.