(Image credit: Shutterstock) As a proud member of the stiff shoulders gang, I can relate to how painful it is to have a limited range of motion in your shoulders and tension in your upper body. Hunching, weak core muscles, tech neck...they all take a beating on posture over time, but you can make some big improvements with this 60-second mobility exercise. You don't need any equipment, but optional extras include a set of light dumbbells and perhaps one of the best yoga mats to protect your knees, as you will be holding a lunge position. I also recommend performing this near a wall, and you'll find out why. Article continues below What is the exercise? To do this exercise, I recommend a wall to your side, then follow these steps: Kneel next to a wall so that it is to your left.…