One factor that can dramatically affect the load on the lumbar spine is body position. When the body is in an upright position, the line of gravity passes anterior to the spinal column As a result, the spine is under a constant, forward bending moment. As the trunk is progressively flexed, the line of gravity shifts farther away from the spine. The farther the line of gravity from the spine, the larger the moment arm for body weight and the greater the bending moment generated. To maintain body position, this moment must be counteracted by tension in the back muscles. The more tension that is required to maintain body position, the greater the compression load on the spine. Lifting with the trunk being erect minimizes the tension requirement for the lumbar muscles, because the moment arm for body weight is minimized. For the same reason, holding the load as close to the trunk as possible during lifting and carrying minimizes the load on the back. In comparison to the load that is present during upright standing, compression on the lumbar spine increases with sitting; increases more with spinal flexion; and increases still further with a slouched sitting position. lists guidelines for preventing lumbar spinal stress during performance of daily activities