If your shoulders feel exhausted after carrying a pack all day, it could be because the muscles that contribute to proper spinal alignment are weak. Karen Asp, a certified fitness instructor, recommends the following simple, at-home exercise to strengthen your shoulder adductors: Lie face down on the floor, with your forehead resting on the ground and your arms stretched out to your sides at shoulder level. Slowly lift your arms upward off the ground, squeezing the shoulder blades together. Gradually lower your arms toward the floor, keeping your hands in line with your shoulders. Perform two to three sets of 12 to 16 repetitions daily. Happy load hauling.