noun
back muscles; muscles of the back
Refers to the muscles along the spine, often in contexts of posture, exercise, or anatomy.
背筋を鍛えると姿勢が良くなる。
Training your back muscles improves your posture.
重いものを持ち上げるときは背筋を痛めないように注意してください。
When lifting heavy objects, be careful not to strain your back muscles.