You have probably heard the claim that bad posture causes back pain, or that you should work on your posture to get rid of low back pain. You can find this claim all over the internet - from physical therapists, chiropractors and personal trainers. If you do a Google search for “posture and pain,” you get 4 million hits.
With so many posture police on patrol, you will almost certainly be told sooner or later by some authority that your posture needs work.
For example, if you have a relatively large curve in your upper back (kyphosis), you might be told that you have “upper cross syndrome.” This pattern involves rounded shoulders, a sunken chest, and a forward head. Common "corrections" are to stretch the chest muscles and strengthen the muscles between the shoulder blades.
Or, if you have a relatively large arch in your low back (lordosis), you may be told you have lower cross syndrome. In this pattern, the pelvis tips down in front (anterior pelvic tilt), and the stomach protrudes forward. To fix this, most people will tell you to strengthen your abs and glutes, stretch your hip flexors, and spend time during the day sucking in your gut and/or keeping your core active.
Another popular idea is that asymmetries cause pain. For example, a therapist may try to identify and correct a twist or tilt in the alignment of your pelvis, because they’re worried this will rotate or bend your spine. They may be interested in whether one of your legs is longer than the other, because this will tilt one side of your pelvis higher than the other.
These ideas have intuitive appeal, and are advocated by numerous experts. But are they supported by evidence? And should you spend time trying to analyze your own posture and correct deviations from what is considered optimal?
Let’s look at some evidence that might help us answer these questions. Although you wouldn’t know it from reading most books or articles, there are many studies looking for associations between pain and measures of postural alignment. And most of them find none. Let’s take a look.
What do studies find on the connection between posture and pain?
Research looking for correlations between back pain and posture typically involves one of several different study designs.
In cross sectional studies, researchers recruit people and divide them into groups -- those with and without back pain. Then they use x-ray, radiograph, or some other means to measure pelvic or spinal alignment, such as leg length discrepancy, pelvic tilt, degrees of curvature in the low back, upper back, or neck. After these measurements are made, researchers determine whether there are significant differences in postural alignment between the groups with and without pain.
In prospective studies, researchers analyze the posture of a certain group of people without back pain, and then determine whether the subjects with a certain posture are more or less likely to have low back pain in the future.
Although the results from these studies aren’t completely clear, most do not support the claim that bad posture causes back pain. Here are some representative findings:
- No association between leg length inequality and back pain. 
- No significant difference in lumbar lordosis or leg length inequality between three groups of 321 males with severe back pain, moderate pain, or no pain. 
- No association between measurements of neck curvature and neck pain.
- No significant difference in lumbar lordosis, pelvic tilt, leg length discrepancy, and the length of abdominal, hamstring, and iliopsoas muscles in 600 people with and without back pain. 
- Teenagers with postural asymmetry, excessive thoracic kyphosis and/or lumbar lordosis were no more likely to develop back pain in adulthood than peers with “better” posture. 
- Pregnant women with greater increases in low back curve during pregnancy were no more likely to develop back pain. 
- People who work occupations involving frequent awkward postures do not have higher levels of back pain. 
Although some studies have found a positive association between measurements of spinal alignment and pain, these are exceptions to the rule. [8, 9]
The weight of the evidence is probably best represented by a systematic review done in 2008, that analyzed more than fifty-four studies on the the link between pain and posture.  Although the quality of the studies was generally poor, together they did not produce evidence supporting an association between measurements of sagittal (back to front) spinal alignment and pain.
The above research indicates that if any correlation exists between posture and pain, it is weak. These results are striking given that many studies have found other factors that correlate with low back pain, such as exercise, job satisfaction, educational level, stress, and smoking. 
Even if a correlation between pain and posture does exist, this would not prove a causal relationship. It may be that pain causes bad posture, and not the other way around. This is very plausible. People who are injected with a solution causing back pain will spontaneously adopt different postural strategies.  Big surprise!
Moreover, even if bad posture does contribute to back pain, it is yet another leap to conclude that posture can be corrected. And yet another to prove that correcting “bad” posture will reduce back pain.
Why is there no association between pain and posture?
The above evidence is surprising and counterintuitive. Why is there no link between pain and posture? There are at least three plausible reasons why posture does not associate well with pain.
1. Tissues adapt to stress over time
The theory that bad posture causes pain is based on the idea that it places excess mechanical stress on certain areas, which causes micro damage that accumulates over time. Although this makes sense, it fails to consider that tissues have the capacity to adapt to stress.
Just as your muscles will get stronger when exposed to the stress of lifting weights, your joints, ligaments, and tendons will adapt to withstand the local stresses created by particular postures. 
2. Tissue damage does not equal pain
The second reason that posture does not correlate with pain is that even if bad posture causes tissue damage, tissue damage does not equal pain.
There are many studies on the prevalence of various kinds of tissue damage in people without pain. These consistently show that large percentages (e.g. 20-50%) of people with pain-free backs, shoulders or knees have bulging discs, tears in the rotator cuff, or torn menisci.  The fact is that almost no matter where you point an MRI on a person over 30, you have a very strong chance of finding significant damage there, even in places without pain.
The reason? Pain is complex, and tissue damage is only one contributor to pain.  Thus, to the extent that posture is causing some form of long-term tissue damage, it will not necessarily result in pain.
3. Different people are different
The third reason that seemingly “bad” postures do not correlate with pain is that everyone has a unique structure. If you look at skeletons from real people, you will see substantial differences in the shape of the bones and spinal curves. Asymmetry and irregularity are the rule, not the exception.
The size and shape of the bones will to some extent dictate the most efficient and comfortable way to stand, sit or move. Therefore, what is “dysfunctional” alignment for one person might be optimal for another.
Because of these individual differences, comparing your posture to some ideal model and trying to make corrections is inherently problematic.
What to do instead of worrying about posture
The above evidence suggests that it may be a waste of time to try to identify defects in your static posture according to some ideal model, and correct them as a way to treat or prevent pain.
So if posture doesn't matter so much, does that mean we shouldn't worry at all about the alignment of the body during rest or exercise? I think the answer is no.
1. Ensure good alignment when high forces are involved
Don’t misinterpret the research on posture to mean that biomechanics and good form don’t matter at all. Vigorous exercise is different than just sitting or standing around, and it may require more attention to proper alignment.
During static standing or sitting, the mechanical stresses on your joints are very small. Your body has experienced these exact stresses thousands of times per day for many years, and is well adapted to handling them.
By contrast, during strenuous exercise, such as a heavy deadlift, the mechanical stress is far greater, and your body has had less opportunity to adapt to those specific stresses.
So your posture and alignment matters in a heavy deadlift. It matters when you land a jump. It matters when you sprint, lift weights, or engage in any activity involving a great deal of mechanical stress. In these cases, it is a good idea to use conscious effort or coaching to ensure that your biomechanics and spinal alignment are optimized to distribute stress, reduce risk of injury and increase performance.
2. Work on your movement
The way you move is more important than how you look standing or sitting. So don’t worry if your chest slumps while sitting at work. But make sure you preserve your ability to fully extend the chest to allow functional activities like overhead reaching, rotating, or pressing weight overhead.
3. Vary your posture
Many people need to sit or stand in the same basic posture for many hours at a stretch. If this is causing stress and pain, subtle variations in posture are a better strategy for comfort than maintaining one “perfect” posture the whole time. Variation will distribute the stress of supporting your body weight to many areas as opposed to concentrating that stress in the same places. Take frequent breaks and keep moving. And if a particular position aggravates back pain, experiment with alternatives.
Forget good posture: think good movement
To sum up, don’t worry too much about trying to change your static posture to conform to some ideal. It is not a likely contributor to back pain. Instead, stay comfortable, keep moving, work to improve your function, and make sure to use good alignment and form when engaged in strenuous exercise.
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Thanks to Armi Legge for help editing this article, which also appears in a similar version at his excellent website called EvidenceMag. EvidenceMag is well worth your time if you are interested in evidence based and well referenced information on how to improve your health and performance.