Drivers Beware:
Lumbar Support Can Be Harmful To Your Health!

 

Don't Let Your Sitting Posture Turn You into a Shallow Breather!

by Dennis Zacharkow, PT
© 2018


Figure 1.
Circle denotes the area of the lower thoracic spine (T10-T12) responsible for the hinging forward and downward of the rib cage.


Figure 2.
A slumped sitting posture results in a relaxation of the abdominal muscles, a lowered position of the diaphragm, and a forward migration of the pelvis on the seat.


Figure 3.
Upper chest breathing results in overuse of the scalene muscles of the neck to elevate the upper rib cage against gravity.

Figure 4.
Deep diaphragmatic breathing is optimized with sacral and lower thoracic support. Note in particular the raised position of the diaphragm, and the greater depth and expansion of the lower rib cage.

The hinging forward and downward of the rib cage, due to flexion of the lower thoracic spine, is the main cause of a slumped sitting posture (Zacharkow, 1988, 1998). (See Figure 1.)

With a slumped posture, "the chest is necessarily lowered, the lungs are much less fully expanded than normal, the diaphragm is depressed, the abdominal wall is relaxed, so that with the lessened support of the abdominal wall, together with the lowering of the diaphragm, the abdominal organs are necessarily forced downward and forward" (Goldthwait, 1915).

The forward and downward displacement of the abdominal organs due to the relaxed, protruding lower abdominal wall and the lowering of the diaphragm, also results in a forward migration of the pelvis on the seat. (See Figure 2.)

This forward migration of the pelvis on the seat is the second cause of a slumped sitting posture.

The typical slumped sitting and driving posture not only restricts diaphragmatic breathing, it also promotes unhealthy upper chest breathing. Shallow upper chest breathing results in overuse of the scalene muscles (Figure 3), a major cause of fatigue, neck pain, referred arm pain, and thoracic outlet syndrome.

So, how effective are the three major seating concepts in correcting/preventing a slumped sitting posture, and thereby optimizing diaphragmatic breathing?

  1. The Lumbar Support Concept

    Using a lumbar support results in a passive sitting posture that relaxes your core. It is located too low on the spine to correct the hinging forward and downward of the rib cage.

    As a passive sitting posture with relaxation of the deep lower abdominals, using a lumbar support cannot correct the lowering of the diaphragm. So, using a lumbar support actually restricts healthy diaphragmatic breathing.

    Lumbar support is also located too high on the spine to stabilize the pelvis on the seat.

  2. The Forward-Sloping Seat Concept

    Advocated by Mandal (1976, 1981), and today recommended by most physical therapists, a forward-sloping seat involves sitting with the hips 10 to 20 degrees higher than the knees. This is usually accomplished by adding a seat wedge to the chair seat.

    The major problem with forward-sloping seats is that the sitter is "intrinsically unstable" (Corlett and Eklund, 1984). These seats destabilize the body by causing the pelvis to slide forward on the seat (Oborne, 1982; Branton,1970).

    Deep diaphragmatic breathing is inhibited because it will destabilize the sitter even further, due to the large displacement of the Center of Gravity with each deep breath (Branton, 1966; Bouisset and Duchene, 1994).

    The tendency will be for sitting on a forward-sloping seat to favor shallow, upper chest breathing. This shallow inspiration will minimize the displacement of the Center of Gravity and the resulting postural instability, but it will lead to a chronic state of fatigue. Holding one's breath will further minimize the displacement of the Center of Gravity.

    In addition, forward-sloping seats do not correct the hinging forward and downward of the rib cage (Bridger, 1988; Drury and Francher, 1985).

  3. The Sacral-Lower Thoracic Support Concept

    Developed by physical therapist Dennis Zacharkow, the sacral-lower thoracic support concept is the only seating concept to address both causes of a slumped sitting posture:

    1. The hinging forward and downward of the rib cage due to flexion of the lower thoracic spine.
    2. The forward migration of the pelvis on the seat.

    As a result, with the sacral-lower thoracic support concept, deep diaphragmatic breathing is optimized. (See Figure 4.)

    Sacral Support

    Maintaining gentle pressure against the sacral support activates the deep lower abdominals, and raises the resting position of the diaphragm at the start of inspiration (Zacharkow, 1998). As the diaphragm descends, this deep lower abdominal muscle activity optimizes diaphragmatic breathing by preventing excessive shortening of the diaphragmatic muscle fibers. This inspiratory abdominal muscle activity also improves the diaphragm's ability to lift the lower ribs, thereby expanding the lower rib cage.

    Also, by stabilizing the pelvis against the sacral support, the forward migration of the pelvis on the seat is prevented.

    Lower Thoracic Support

    Only lower thoracic support corrects the hinging forward and downward of the rib cage, resulting in an elevated rib cage.

    Dramatic improvement in diaphragmatic breathing occurs for two reasons with lower thoracic support:

    1. Mechanical support to the lower thoracic spine elevates the rib cage and prevents its downward movement. This mechanical support immediately reduces some of the static load on the scalene muscles.

    2. The pressure from the lower thoracic support against the lower thoracic region of the back immediately facilitates proper diaphragmatic breathing by eliciting what are called the intercostal-to-phrenic reflexes (Decima et al., 1969; Leanderson et al., 1987). In other words, the nerve connected to the diaphragm muscle (the phrenic nerve) is under the control of reflexes that are activated by sensory stimulation of other nerves in the region of the lower thoracic spine. Pressure from the lower thoracic support against this specific region of the back is a simple way to elicit these reflexes.

Conclusion

Being a healthy diaphragmatic breather when sitting and driving is easy! Just forget what you've been taught, and stabilize your posture with sacral and lower thoracic support.

References

  • Bouisset, S., and Duchene, J.L.: Is body balance more perturbed by respiration in seating than in standing posture? NeuroReport, 5:957-960, 1994.
  • Branton, P.: The Comfort of Easy Chairs. Stevenage, Hertfordshire, England, The Furniture Industry Research Association, 1966.
  • Branton, P.: Seating in industry. Applied Ergonomics, 1:159-165, 1970.
  • Bridger, R.S.: Postural adaptations to a sloping chair and work surface. Human Factors, 30(2):237-247, April 1988.
  • Corlett, E.N., and Eklund, J.A.E.: How does a backrest work? Applied Ergonomics, 15:111-114, 1984.
  • Decima, E.E., von Euler, C., and Thoden, U.: Intercostal-to-phrenic reflexes in the spinal cat. Acta Physiologica Scandinavica, 75:568-579, 1969.
  • Drury, C.G., and Francher, M.: Evaluation of a forward-sloping chair. Applied Ergonomics, 16:41-47, 1985.
  • Goldthwait, J.E.: An anatomic and mechanistic conception of disease. The Boston Medical and Surgical Journal, 172:881-898, 1915.
  • Leanderson, R., Sundberg, J., and von Euler, C.: Role of diaphragmatic activity during singing: a study of transdiaphragmatic pressures. Journal of Applied Physiology, 62:259-270, 1987.
  • Mandal, A.C.: Work-chair with tilting seat. Ergonomics, 19:157-164, 1976.
  • Mandal, A.C.: The seated man (homo sedens). Applied Ergonomics, 12:19-26, 1981.
  • Oborne, D.J.: Ergonomics at Work. Chichester, Wiley, 1982.
  • Zacharkow, D.: Posture: Sitting, Standing, Chair Design and Exercise. Springfield, Thomas, 1988.
  • Zacharkow, D.: ZackBack Sitting. Rochester, ZACKBACK International, 1998.

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