The Study: Effects of the posterior pelvic tilt sitting posture on thoracic morphology and respiratory function

Overview: This study examines how differences in pelvic angle in the posterior pelvic tilt sitting posture affect both thoracic posture and related respiratory function. Posterior pelvic tilt sitting (PPTS) posture has been previously recognized as a sub optimal posture and a strong relationship between pelvic angle, lumbar alignment and LBP has been reported.

Key Points: 

a)      The participants were 18 healthy young males. 

b)      Participants were positioned in sitting position with the pelvis at 0°, 10°, 20°, and 30° of posterior tilt,

 c)      Thoracic movement during breathing, thoracic spine tilt angle, and respiratory function were measured in each of the four seated postures. 

d)      The authors calculated both the thoracic volume and thoracic spine tilt angle by measuring the amount of displacement of reflective using the Vicon MX 3D-motion analysis system. The system employed an array of eight cameras which observed the motions of 70 infrared reflective markers placed at specific points on the chest and back.  

e)      Respiratory function was measured over several parameters using spirometry. 

Results: 

f)        The upper thoracic spine level showed increased anterior tilting at 10–30° posterior pelvic tilt sitting

g)      The lower thoracic spine level showed increased posterior tilting at 30° posterior pelvic tilt sitting.

 h)      Respiratory Function using spirometry was significantly reduced at 30°posterior pelvic tilt sitting than at 0° posterior pelvic tilt sitting. 

i)        A positive correlation between Thoracic Expansion Volume Ratio and Respiratory Function was found at 30° posterior pelvic tilt sitting.

 j)        The total Thoracic Expansion Volume Ratio was unchanged from 0-10 degrees but was significantly decreased once the PPTS exceeded 20 degrees.

 k)      Respiratory function was significantly decreased at 30 degrees of PPTS. Previous studies have reported similar findings of the relationship between PPTS and decreased respiratory function.

 l)        The authors posit that respiratory impairment may be due to changes in rib angles in PPTS which restrict thoracic excursion during respiration as well as compression of internal organs and resulting restriction of diaphragm motion.   

Author’s Conclusions: Thoracic expansion volume ratio, thoracic spine tilt angle, and respiratory function was measured in four PPTS postures. The results showed that thoracic expansion volume ratio is altered by the degree of PPTS and that changes in thoracic spine tilt angle affected the thoracic expansion volume ratio “which can critically affect respiratory function”.. Evidence of impaired respiratory function was demonstrated with spirometric assessment.

Reviewer's Comments: The thoracic changes noted in items F and G (see above) would seem to be consistent with increased thoracic kyphosis, (which, at least to my mind) would likely restrict both rib movement and diaphragm excursion. Increased thoracic kyphosis has been previously associated with decreased lung function. To be clear, this study does not specifically mention any changes in the thoracic kyphosis, however the observed postural changes in both the upper and lower T spine are suggestive of increased thoracic curve. Perhaps the relationship between habitual seated postures/thoracic kyphosis and respiratory function are worth considering in your practice.

Finally, posterior pelvic tilt during sitting can often be reduced with the use of a forward tilting seat wedge. ( Here’s a link https://www.matlinmfg.com/products-overview/seatwedge ) I have previously recommended this type of simple, low cost solution to help support and reinforce the lumbar lordosis. This study offers another compelling reason to consider working to improve your patient’s seated posture.  

Reviewer:  Mark R. Payne DC

 Reference:  Yoshihiro Aramaki, PT, MS1, 2), Fujiyasu Kakizaki, PT, PhD, Shinichi Kawata, PhD, Takuya Omotehara, PhD, Masahiro Itoh, MD, Phd. Effects of the posterior pelvic tilt sitting posture on thoracic morphology and respiratory function. J. Phys. Ther. Sci. 33: 118–124, 2021 

Link to Abstract: https://pubmed.ncbi.nlm.nih.gov/33642685/

Link to Full Text: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7897525/