Low back pain (LBP) is a major problem of the industrialised society. In order to protect our back, it is useful to strengthen our abdominal muscles. Strong abdominal muscles can contribute to spinal stability by increasing intra-abdominal pressure(IAP). This converts the abdomen into a rigid cylinderlike structure with a stable spine. TA- because of its horizontal orientation, is most effective in raising IAP. There is, sadly,  no gold medal exercise for the back in that none are found to be most effective, but a sensible combination can help patients. However, many of these exercises , if not performed properly , can do more harm than good by intensely loading the lumbar spine. 

These exercises are recommended by the North american spine society. If they increase back pain they should be stopped. The rules are to do them:
slowly, regularly, to start with five repetitions of each exercise, and work up to ten repetitions.

Modified Sit-up - Slowly raise your shoulders off the ground while keeping your chin tucked. Touch your fingertips to your knees and hold for the count of five. This exercise activates IO and RA units. Do not arch your back. Keeping the back straight helps to reduce spinal motion and hence the load. A popular variation is to perform the exercise with the hands clasped behind the head. This should be avoided as it increases the moment by moving centre of gravity of upper body away from the centre of spinal motion. 

Straight Leg Raise- This strengthens the leg and abdominal muscles. Lie on your back with one knee bent so the foot is flat on the floor; keep the other leg straight and slowly raise it 8" off the floor. Hold for five seconds, lower and relax; repeat five times then change legs.

Hamstring Stretch: Hamstring tightness is common in patients suffering from LBP. Hamstring stretch is very useful for the back. It can be done standing, sitting or lying down. Standing - Stand with one leg straight out in front of you, your foot resting on a table or chair. Bend the leg you are standing on until you feel a mild stretch under the thigh of the raised leg. Hold for a count of three. Sitting - Sit on the floor with one leg straight in front of you, and the other bent with your foot flat on the floor. Lean forward slowly over the bent leg until you feel a mild stretch under the other thigh. Lying down - Lie on your back with your knees bent so your feet are flat on the floor. Raise one leg slowly, clasping your hands behind your knee to support it. Slowly straighten your leg and feel the stretch in the back of your thigh. Hold for a count of three then relax.

Reverse curl: This exercise also activates the IO, EO & RA muscles while limiting Psoas activity- thus disc pressure quite low.Lie on your back with your knees bent and feet flat on your bed or floor. Raise your knees toward your chest. Place both hands under your knees and gently pull your knees as close to your chest as possible. Do not raise your head. Do not straighten your legs as you lower them. ( From AAOS ) 

                                                                   Ergonomics

Poor Posture is an important cause of back fatigue and pain. Especially with the advent of computers, we spend a lot of time sitting, it is important to understand requirements for a good chair and good posture. 

An ideal chair supports the back with minimal effort from the back muscles. 

Arm rest: Because our shoulder girdle hangs freely from the axial skeketon, provision of a arm rest supports their weight and unloads the girdle. Resting the hands on the lap or arm rests can take up to 25% of the load off the lower back.

Back support: Prolong sitting without a back support always results in the spine assuming a C form. They support the back and also prevent the lumbar spine going into kyphosis. The best angle between seat and backrest is between 90- 95 degrees. This accommodates the buttocks at the lower level. A firm lumbar support at the lumbar level is essential for this. This should be lower than scapular blades. 

Seat: A slightly inclined seat surface reduces friction at the ischial tuberosities. It should not be too high as to avoid thigh pressure. 

Head rest: A good head rest supports the weight of the head and off-loads the neck muscles. To be effective, it should be positioned rather backward so that centre of gravity of head is dorsal to the axis of atlanto-occipital (AO) joint. Then there is a natural tendency for the head to fall backward, which is supported by the rest. If placed forward, the centre of gravity is anterior to the AO joint and head tends to fall forward, necessitating the neck muscles to be active. 

No chair is perfect and the best policy is to avoid long sitting in one position.Most important safety technique is to change posture on a regular basis.

Examples of bad sitting: ( from Benjamin Rossen)

This individual is slouching forward and sitting on the chair edge. This spares fatigue on the dorsal muscles at the cost of increased intervertebral pressure. As the reading distance is long, spine and neck is bent, this can increase neck muscle fatigue and neck injury can result as well. 

 a typical lazy slump:

In the absence of good back support,here, the worker has assumed the C position with kyphosis of the L spine. This position places stress on all levels of the back, neck, shoulders and arms.