Your Bad Posture Might Not Just Be From Your Upper Back and Shoulders! Most people focus on fixing their upper back or shoulders to improve posture — and that’s a great start — but what’s happening at your pelvis plays an even bigger role. Sitting all day can either: * Tighten hip flexors * Cause your pelvis to tuck under, rounding your lower back and weakening the glutes, inner thighs, and deep core muscles that stabilize your spine. Here’s a simple fix: 1. Sit tall at the edge of chair/ pillow