It's probably clear by now that even though you can't work on your cardio or set a new bench-press record at a stop light, you can improve your posture. We've already touched on the abdomen and the shoulders -- but what about the neck? "Those muscles on the back of the neck are going to help you hold your head upright and give proper posture," Peterson says. You can strengthen these muscles with the chin tuck. Push the back of your head against the headrest and use your neck to drive your chin down into your chest, exaggerating each movement. Hold each repetition for one second and perform 15 repetitions [source: Peterson].