Maintaining the natural curves demands good posture and can only be accomplished with firm muscles. The muscles act like guide wires to support the spinal column, and if they become fatigued, they can't properly position and support the spine. More stress is then put on the bones and joints.
Weightlifters spend hours lifting tremendous weights and suffer few back problems. They maintain their body much like a mechanic would fine tune a machine. By lifting weights, lifters maintain the three natural curves of the spine and use the muscles of the abdomen, buttocks, and thighs.
This group of muscles is much stronger than those in the back, so it is real important to keep them in good shape. Loss of muscle tone from over eating and lack of exercise can develop poor posture.
When the abdomen thrusts out, the muscles in the back work to offset the muscles in the front. Women in the last month of pregnancy have the same problem. Slouching or rounded shoulders can cause muscles to be overworked and increase the work of the spine.
Any change of the normal curve of the spine is poor posture and affects the amount of work the back must do. Lifting a load is one of the main causes of back pain. From the time you get up in the morning and until you go to bed at night, you will invariably have to pick up or lift and object and it will continue throughout the day.
Even picking up a small object such as a pencil, if not done correctly, can irritate your back. You can protect your back by practicing proper work habits all the time.
Think of your back as a lever system. The distance between the load and the fulcrum can be up to 10 times greater than the distance between the fulcrum and the point where the lifting force is supplied.
With this ratio it would take a lifting force of 100 pounds to lift 10 pounds. When you lift a load, keep it close to the body. Lifting without doing this will require the lever to apply a force much greater than the weight of the object itself.
Just bending over with only the weight of your head, arms, and upper body can exert 1,200 pounds of pressure on the back. Add 50 pounds and this will exert 1,700 pounds of pressure to your back.