If you have bad posture, chances are you already know. (It was probably the eternal aching in your shoulders that tipped you off.) But annoying aches and pains aren't the only thing that chronic slouching can do to your body — the real biggie is that it can weaken your muscles, making you more vulnerable to serious injuries. Poor posture can be caused and exacerbated by many things. For instance, if you're stuck at a computer all day, your shoulders may hunch forward and your back may slouch for hours at a time. Then, if you've got depression or any other chronic health problem, that stress and inflammation can just make those tight muscles worse. If you don't exercise or stretch regularly, that discomfort will also make it difficult to get to sleep at night. And then you'll wake up stiff and the whole cycle will start again. So, ultimately, your bad posture is both caused by and contributes to tight, weakened muscles. In particular, you'll notice tightness in the muscles in your shoulders, neck, and back. So relaxing and beefing up those muscles is a logical place to start. But you'll also need a solid core to discourage you from slouching and prevent lower-back injuries. That means that the best way to improve your posture and keep your back safe is to strengthen all of those muscles — basically your whole upper body and core. That might include moves like shoulder rolls, core-building golf swings, and exercises such as YTW or "angels" that ease tension in your upper back and help build the muscles that keep your shoulders in the right place. But because everyone's body is a bit different, it's best to check in with a physical therapist (your regular doctor can recommend one). He or she will then give you exercises specific to your issues. However, experts generally don't recommend using a brace or jumping into a rigorous new fitness routine to fix the problem, as these can actually further weaken or damage those muscles. So stretch it out — but start slow. And talk to your doc for extra guidance.