"Back muscles" refers to the group of muscles located in your back, which help support your spine and allow you to move and maintain good posture. Full definition
The lower back muscles work with the abdominal muscles in order to keep the spine stable, improve sports performance, and decrease the risk of injury or back pain. (ab-core-and-stomach-exercises.com)
Since you are in a fixed position, the seated cable row is the perfect exercise to help develop all the middle and upper back muscles in the body. (theathleticbuild.com)
And because the strength of back muscles contribute significantly to early walking, stimulate her muscles by giving her more tummy time. (toptenstrollers.com)