My posture sucks. Ill admit it. As Im sitting here, my shoulders are almost touching the keyboard. And I’ll bet you are all Hunchy McHunchersons right now as well. And I bet all of you just sat up a little straighter as you read that.
While for some, poor posture is do to excessive weightlifting without stretching the chest because “stretching is girl stuff” (if you are muscle bound and have this problem, stretch your chest for goodness sake.)

yuck.
For most of us, it is due to The Computer Age.

As we spend more and more time in front of the computer, the muscles that hold us upright get weaker and weaker, making that Quasimoto spine curvature a permanent look.
While you can’t really help how much time you spend in front of the computer or at your desk, you can counteract the slump by strengthening the muscles that will pop you up right.
Its all about imbalance.
The Primary muscles that affect your posture are:
The Core
Your core are the muscles that surround your spine, supporting and protecting it. It is not just your abs, but your lower back muscles as well. A lot of people think Core=Abs, which leads to unequal core strength. Only working the abs while neglecting the rest of your core will lead to an imbalance. If your abs are strong and tight, and the lower back muscles are not strong enough to balance them out, you will tend to lean forward. To strengthen all the way around try Supermans, Back Extensions, or Planks(this guy’s hips are a little hip, you want them level with your body) and Side Planks.
Core imbalance can also cause a lot of lower back injuries, or just plain soreness. Keep everything balanced and even to avoid unneccessary injury.
The Upper Back
Just like the core, if one area is tight and the other is weak, the body will shift in favor of the strong, tighter area. The chest tends to be stronger, and thus tighter, than the upper back, so we tend to get the sunken chest, slumped shoulders thing goin’ on. To build the upper back and pop those shoulders back, try Rows, Lat Pull Downs, and Reverse Flyes( you can also do these laying on a stability ball).
The Hip Flexors
This ones kind of suprising. “What could my hips have to do with my posture?” you may be asking. Well, stop interupting me and Ill tell you.
Your hips flexors connect your quad area to your lower ab area. The hip flexors are notorious for being tight. Think about it. How often do you flex your hips? (think bringing your knees to your chest or kicking straight out in front of you) Every time you take a step, right? so they are quite strong. Now how often do you extend them? (think kicking backwards, leg straight, or lunging, back leg straight) Hardly ever, right? When the hip flexors are tight, they are shortened. This pulls the whole torso forward, all the way up to your shoulders. Nuts, right? To fix the hip flexor problem, you really just need to stretch them, which you can do, one at a time, but getting into lunge postion, but tilting your hips backwards to get a little extra pull.
To keep your body upright and standing tall, stay consistant with your strength training. Think of your body as being segmented into opposites (chest and back, quads and hammies, abs and lower back), and training them both equally.
And I bet during the course of reading this you went right back to slouching again. I did.