Muscle spasms are the most common cause of low back pain. That’s why some treatments include muscle relaxers. You can strain a muscle with an unexpected pull or twist. Your risk of muscle spasms increases if you have weak stomach muscles, tight hamstrings, any back weakness, or a pelvis that tilts forward more than normal.

About 80% to 90% of U.S. adults get low back pain at some point in their lives. Men and women are equally affected. Low back pain is more common as we get older, with people often having their first episode between ages 30 and 50. But it also can be the result of a sedentary lifestyle -- with too little (and occasionally too much) exercise.

And low back pain is the fifth most common reason for doctor visits.

Bed rest alone can actually make back pain worse. It can also lead to other conditions, like weakened muscles and blood clots in the legs. One study showed that patients who continued their normal activities after a bout of low back pain had more flexibility than those who rested in bed for a week. Staying in the same position for too long can also make your joints stiff.

The lower back consists of five lumbar vertebrae. They are the weight-bearing part of the back and receive the most stress. The mid back is made up of 12 thoracic vertebrae. The ribcage attaches here. This part of the back is very flexible to allow bending and  twisting. The seven cervical vertebrae are located in the neck.

Most of the time, you do not need an imaging test when you have back pain, particularly because most imaging tests won't reveal a muscle spasm or ligament sprain. But your doctor may still order an imaging test if you suffered a back injury or if the pain doesn't get better after several weeks.

Most back pain is caused by injury to the lower back or an ongoing condition. Overuse of the back muscles, sports injuries, extreme lifting, or sudden jolts -- such as a car accident -- are examples of injury. Arthritis or a bulging disc are ongoing conditions that may cause back pain.

Acute – or short-term – low back pain begins suddenly and may last several days or weeks. Chronic low back pain, which can be mild or severe, lasts longer than three months.

After the first flare-up, you might take a short rest period  -- one to two days -- applying ice for the first couple of days and then a heating pad to loosen tight muscles. Take an over-the-counter pain medication if you need it. You should try to stay active as much as possible. If you do choose a day of bed rest, try to walk around every couple of hours. Movement can help speed up healing. You should see your health care provider if the pain doesn’t improve or if it gets worse within seven to 10 days.

Firmer may not always be better. People who sleep on a medium-firm mattress are twice as likely to report that their back pain decreased while lying in bed or getting in or out of bed. So if you think you prefer a firm mattress, you might want to try medium-firm. Softer mattresses may place less pressure on the shoulders and hips, allowing you to sleep in a more natural position on your side. Your mattress should be firm enough to maintain your spine in the position you have with good standing posture.

Things like chiropractic care, physical therapy, yoga, and massage may help. In fact, groups such as the American Pain Society and American College of Physicians recommend these complementary and alternative treatments for people whose pain continues after more than a few weeks of self-care.

You should see a health care provider for back pain if you have any of the above symptoms or fever, weakness, trouble urinating, numbness in your legs, or weight loss when not on a diet. Most short-term low back pain is treatable without surgery, but these other symptoms may point to a more serious problem.

Fewer than 2% of people with back pain have a herniated or slipped disk -- a bulging disk that presses on the nerves next to it. Most people with low back pain improve with treatment of heat and ice, rest, gentle exercise, and over-the-counter pain relievers.

Sciatica is leg pain caused by pressure on the sciatic nerve. The most common cause is a slipped disk. Other conditions, such as a narrowing of the spinal canal, also may cause sciatica. The sciatic nerve extends from the spine to  each leg. Pressure on the sciatic nerve causes shock-like or burning pain in the lower back and buttocks and typically down one leg. The pain occasionally reaches the foot.

There are a few spinal conditions that involve twisting and spinal pain. Scoliosis – or curvature of the spine -- is marked by a bending of the spine to the side. Kyphosis, which means "humpback,"  means the spine is bent forward. Lordosis, or “swayback,” means the spine has a backward curve.