The outboard lats run from the armpit down to the small of the back. They are used to pull the shoulders downward; they also assist in pulling the elbows in towards the sides.
The upper lats which run from the armpit to the spine—in the area under the shoulders—are used to pull the shoulders back and also to swing the elbows outward.
To work these you would do lat pulldowns (it's a machine at the gym). Pull-ups would also work for your lats.
Basically, wide-grip movements will primarily hit the upper lats. This is also pretty much the case with bent rowing (barbell or dumbbell) or seated rowing.
On the other hand, close-grip overhead work will primarily hit the outboard lats; this is particularly true when you use an undergrip or palms up grip.
If you want to work your lower back or spinal erectors, try doing stabilizers AKA tabletops or coffee table. Think pushup position here, except your body weight should be resting on your forearms instead of your hands. Push your body to the "up" position, tighten your stomach, and keep your shoulders, back, buttocks, and heels in a straight line. Now hold (30 seconds to a minute). This is one of the best exercises for your core (abs and back). [ ellegirl606's advice column | Ask ellegirl606 A Question ]
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