
Your back is the axis of your body, so make it stronger to provide more power for sports and daily activity. Strong, developed muscles also create a V-shape appearance to your torso, so your waist looks a little slimmer. Plus, you'll stand taller with better posture and help ward off back pain, which afflicts 31 million Americans at any given time, according to the American Chiropractic Association.
The many muscles that make up your back include superficial, large muscles that, when strong, look sculpted and cut, as well as deeper muscles that support your spine and are critical to optimal function. Work them all to create a strong, defined backside.
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Superficial Muscles
Some of the most predominant muscles of your back include the broad latissimus dorsi, which spans the back of the ribs and wraps around under the arms; the rhomboids at the back of your shoulder blades; and the trapezius, which lies behind the shoulders, neck and middle back. Work them all to develop a balanced and functioning backside.
Lat Pull-Downs
Target the lats with this gym-standard. You'll also activate the traps as a synergist, or helper muscle.
How to: Sit under a lat pull-down bar attached to free-standing machine or as part of a cable-pulley machine. Grasp the handle with a wider than shoulder-width, overhand grip. Lock your thighs under the padded rests and pull the bar down in front of your collar bones and return your arms back up to full extension to complete one rep.

Shrugs
A barbell is a standard way to perform the shrug, but dumbbells, a Smith press machine, lever machine or cable may be used, too. This isolated exercise targets the upper and middle trapezius.
How to: Grasp a barbell with an overhand grip and allow it to hang in front of your thighs. Pull your shoulders up as high as you can and slowly release down to complete one rep.
Bent-Over Row
Isolating the rhomboids is almost impossible, but moves like the bent-over row, target the rhomboids along with the other primary muscles of the back. The row also engages some of the smaller, but important, muscles of the back, such as the teres major and minor. Inverted rows, dumbbell rows and cable rows work the back in a similar way, also contributing to a strong back.
How To: Grasp a barbell with an overhand grip and hold it in front of your thighs. Bend forward from your hips to at least 45 degrees and as far as 90 degrees. Let the barbell hang toward the floor and then pull the elbows back to '"row" the bar to your navel, or just above. Pause for a brief moment and then release back down to the hang to complete one rep.

Deeper Muscles
The erector spinae, a group of muscles that surround the spine, and the transversospinales, which lies under the erectors, support spine and core strength and good posture. Work these muscles with functional exercises that use your body weight, rather than heavy resistance.
Read More: Exercise for the Erector Spinae Back Muscles
Supermans
Supermans seem simple, but are quite effective in working all the deep muscles of your spine. They contribute to a strong core and better posture.
How To: Lie on your stomach on an exercise mat. Reach your arms overhead, palms facing the floor. Keep your legs extended behind you with the feet hip-distance apart or the thighs zippered together. Inhale and lift your arms, face, chest and legs up off the floor. Pause for a second or two and lower back down to the mat to complete one repetition. Note that if your back feels strained with your arms extended overhead, bend your elbows to create a goal post shape with your arms as you lift into the exercise.

Read More: Superman Lower Back Exercise
Back Extension
One of the primary roles of the erector spinae is to support the spine during flexion and extension. Make your back strong by training this action with the back extension.
How To: Lie stomach first on a Roman chair, which is the apparatus at the gym that looks like a backless seat with foot holds. Hook your feet under the pads at the bottom and lay your hips over the upper pad. Hold a weight plate across your chest, or if you're new to the exercise cross your arms over your chest without a weight, and slowly lower your torso down toward the floor as you hinge your hips. Squeeze your abs and back as you rise back up to complete one repetition.