We're sitting more often and in most cases, longer. Whether it's during leisure or work activities, sitting appears to be a major factor to consider in the treatment of musculoskeletal conditions that present to our office.
Improper sitting has long been seen as a cause of musculoskeletal conditions, whether during leisure or work activities. However, some studies question whether sitting actually leads to such things as low back pain. A systematic review by Roffey, et al. (2010) did not find any high-quality studies that establish causality between occupational sitting and low back pain.1 A systematic review by Chen, et al. (2009) found no correlation between a sedentary lifestyle and low back pain.2
Other research, however, has shown that prolonged sitting, in combination with awkward postures, increases the likelihood of LBP. The two most frequently cited risk factors for LBP from occupational sitting are prolonged static sitting and reduced lumbar lordosis.3 Hence, prolonged static sitting and improper sitting postures are things we can address in our practice as a component of our treatment plan.
When we discuss "proper posture," what does that actually mean? It's commonly defined as the ability to maintain a neutral lordosis position. In order to assess the loads placed on a spine during various positions, Rohlmann, et al. (2011) looked at various seating positions.4 They found the implant force increased 48 percent for 15 degrees flexion and decreased 19 percent for 10 degrees extension of the trunk. Placing the hands on the thighs reduced the loads by 19 percent, on average, compared to having arms hanging at the sides. Another study by Dreischarf, et al. (2010) also found that reduced spinal load during sitting can be achieved by supporting the upper body with the arms.5
Sitting has been associated with a substantial decrease in lumbar lordosis and pelvic measures. A study by De Carvalho, et al. (2010) compared lumbar spine and pelvic posture between standing and sitting via radiologic investigation. Lumbar lordosis and sacral inclination decreased by 43 and 44 degrees, respectively.6 This shows that with respect to sitting posture, to goal should be to maintain or prevent a reduction of the lumbar lordosis.
Distal Effects of Slouched Postures
Neutral sitting postures also provide positive effects to the cervicothoracic spine. One study found 40-percent higher cervical extensor activity in the slouched posture. More neutral sitting postures reduce the demand on the cervical extensor muscles.7 Education on maintaining a neutral sitting posture can offset the detrimental effects.
Another study looked at the effects of forward head posture (FHP) on muscle activity. Significant increases in EMG activity of the upper and lower trapezius, and decreased EMG activity of the serratus anterior, were found during loaded isometric shoulder flexion with FHP.8
Studies are showing a trend toward addressing neck postures through thoracolumbar spine postural adjustments. A study by Caneiro, et al. (2010) showed that slumped sitting was associated with greater head / neck flexion, and increased muscle activity of the cervical erector spinae.9 Adjustments to seat angle and lumbar roll can also significantly effect head and neck posture. A study by Horton, et al. (2010) found that the degree of angulation of the backrest support of an office chair, plus the addition of a lumbar roll support, are the two most important seat factors that will benefit head and neck postural alignment.10
Sitting posture also has impact on the shoulder joint. A study by Bullock, et al. (2005) looked at how sitting posture can affect range of motion and pain for those with shoulder impingement.11 An erect posture appeared to increase active shoulder flexion, although there was no difference in shoulder pain between an erect and slouched posture.
Finley, et al. (2003) found that an increased thoracic kyphosis from a slouched posture can significantly alter the kinematics of the scapula during humeral elevation.12 And Kebaetse, et al. (1999) found that a slouched posture is associated with a 16.2 percent reduction in arm horizontal muscle force.13
Local Effects of Slouched Posture
So far, we've seen how a decrease in lumbar lordosis can impact distal areas of the spine. However, what detrimental effects does a slouched posture position have locally? Repeated forward flexion at the spine can contribute to impaired reflex activation of the back muscles. Prolonged forward-flexed positions can impair sensorimotor control mechanisms and is mainly due to time-dependent "creep" in soft tissues, rather than muscle fatigue.14 Therefore, limiting prolonged forward flexion of the spine is important in helping to maintain proper posture.
Another interesting question to ask is whether the joints of the lumbar spine are fully flexed in a seated posture. A recent study by Dunk, et al. (2009), out of the University of Waterloo, evaluated whether the intervertebral joints of the lumbosacral spine approach their end ranges of motion in a seated posture.15 In upright sitting, the L5-S1 intervertebral joint was flexed to more than 60 percent of its total range of motion. In a slouched posture, each of the lower three intervertebral joints approached their total flexion angles. This shows an increased loading of the passive tissues (time-dependent "creep"), which may contribute to low back pain from prolonged sitting.
Slouched position also has an impact on the thickness of the transverses abdominis (TrA), which is important in spinal stability. A study by Reeve, et al. (2009) assessed the thickness of the TrA in various postural positions. Thickness was significantly greater in standing and erect sitting than in a slouched or sway-back standing position.16 The authors concluded that lumbopelvic neutral postures have a positive influence on spinal stability compared to equivalent poor postures.
A study by Claus, et al. (2009) looked at the effect of various postures on regional muscle activity.17 For the deep and superficial fibers of lumbar multifidus muscles, the least muscle activity occurred during a flat posture, which was similar to a slump posture. The most activity occurred in a short lordosis position; there was also more activity in the obliquus internus.
Proprioception, in the form of lumbar spine reposition sense, is also affected by a slouched posture. A study by Dolan, et al. (2006) provided evidence that a slouched posture of 5 minutes' duration can increase reposition error.18 Proprioceptive control is known to be valuable in spinal stability. The fact that reposition error can occur within as little as 5 minutes of "slouched" posture suggests the importance of postural education in decreasing proprioceptive loss and injury.
This overview of the literature shows that we need to actively address our patients' sitting postures, whether they complain of neck, shoulder or low back pain. Patient education also needs to stress the ability to target the two main culprits in the onset of musculoskeletal pain: prolonged static sitting and decreased lumbar lordosis. Understanding that a slouched posture can have an impact on the passive structures of the spine, in addition to negative effects on proprioception, should help us develop the right treatment strategies for patients presenting with a slouched sitting posture.
- Roffey DM, et al. Casual assessment of occupational sitting and low back pain: results of a systematic review. Spine, 2010 Mar;10(3):252-61.
- Chen SM, et al. Sedentary lifestyle as a risk factor for low back pain: a systematic review. Int Arch Occup Environ Health, 2009 Jul;82(7):797-806.
- Makhsous M, et al. Biomechanical effects of sitting with adjustable ischial and lumbar support on occupational low back pain: evaluation of sitting load and back muscle activity. BMC Musculoskelet Disord, 2009 Feb 5;10:17
- Rohlmann A, et al. Measured loads on a vertebral body replacement during sitting. Spine, 2011 Sep;11(9):870-5.
- Dreischarf M, et al. Different arm positions and the shape of the thoracic spine can explain contradictory results in the literature about spinal loads for sitting and standing. Spine, 2010 Oct 15;35(22):2015-21.
- De Carvalho DE, et al. Lumbar spine and pelvic posture between standing and sitting: a radiologic investigation including reliability and repeatability of the lumbar lordosis measure. J Manipulative Physiol Ther, 2010 Jan;33(1):48-55.
- Edmondstron SJ, et al. Changes in mechanical load and extensor muscle activity in the cervico-thoracic spine induced by sitting posture modification. Ergonomics, 2011 Feb;54(2):179-86.
- Weon JH, et al. Influence of forward head posture on scapular upward rotators during isometric shoulder flexion. J Bodyw Mov Ther, 2010Oct;14(4):367-74.
- Caneiro JP, et al. The influence of different sitting postures on head / neck posture and muscle activity. Man Ther, 2010 Feb;15(1):54-60.
- Horton SJ, et al. Changes in head and neck posture using an office chair with and without lumbar roll support. Spine, 2010 May 20;35(12):E542-8.
- Bullock MP, et al. Shoulder impingement: the effect of sitting posture on shoulder pain and range of motion. Man Ther, 2005 Feb;10(1):28-37.
- Finley MA, et al. Effect of sitting posture on 3-dimensional scapular kinematics measured by skin-mounted electromagnetic tracking sensors. Arch Phys Med Rehabil, 2003 Apr;84(4):563-8.
- Kebaetse M, et al. Thoracic position effect on shoulder range of motion, strength, and three-dimensional scapular kinematics. Arch Phys Med Rehabil, 1999 Aug;80(8):945-50.
- Sanchez-Zuriaga D, et al. Is activation of the back muscles impaired by creep or muscle fatigue? Spine, 2010 Mar 1;35(5):517-25.
- Dunk NM, et al. Evidence of a pelvis – driven flexion pattern: are the joints of the lower lumbar spine fully flexed in seated postures? Clin Biomech, 2009 Feb;24(2):164-8.
- Reeve A, et al. Effects of posture on the thickness of transverses abdominis in pain-free subjects. Man Ther, 2009 Dec;14(6):679-84.
- Claus AP, et al. Different ways to balance the spine: subtle changes in sagittal spinal curves affect regional muscle activity. Spine, 2009 Mar 15;34(6):E209-14.
- Dolan KJ, et al. Lumbar spine reposition sense: the effect of a ‘slouched' posture. Man Ther, 2006 Aug;11(3):202-7.
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