^You are the least specific person possible. Did you sign an NDA? Is this gov't top secret?
OP, he is really referring to shoulder exercises. You likely have weak trapezius muscles in the shoulder, rear deltoids, upper/middle back, and lower back. To fix posture, you could do body weight type exercises or 10-25 lb dumbbells should be plenty. Having stronger muscles means that they won't tire out when sitting in the same position