Posture and Muscle Strength
A central tenant of the corrective exercise approach is that strengthening weak muscles and lengthening short muscles will improve posture (Kendal et al 1993). For example Janda (1987) suggested that his lower cross syndrome, anterior pelvic tilt and increased lumbar lordosis, was due to tight erector spinae and hip flexors coupled with weak lower abdominals, gluteals and hamstrings. Hyrsomallis and Goodman (2001) conducted the last significant review on this topic. They concluded that muscular strength was not related to posture based on the research up to that point. However, deeper analysis of these earlier physiotherapy studies and an appreciation of some of the other factors that influence posture will provide further understanding.
The two key studies on posture and muscle strength both concluded that posture and muscle strength were not correlated. Youdas et al (1996) compared pelvic tilt and lower abdominal strength with lumbar lordosis in 45 men and 45 women with average ages of 57. Abdominal muscle performance was associated with angle of pelvic inclination for women but men. Further, abdominal muscle length was associated with lumbar lordosis in women. In men lumbar lordosis was associated with abdominal muscle length and 1 joint hip flexor length. Interestingly though pelvic inclination and lumbar lordosis was not associated. Despite the associations found neither univariate nor multivariate analysis produced significant correlations between lower abdominal strength, length or hip flexor length or strength with lumbar lordosis or pelvic tilt. Similarly, Walker et al (1987) compared lower abdominal strength with lumbar lordosis in 23 women and 8 men with a mean age of 24. They assessed lower abdominal strength as described Kendal et al (1993). Intra tester reliability was high (0.90) but correlation between lumbar lordosis and lower abdominal strength was only 0.71. Both studies examined strength. Logically muscular endurance should have a more significant correlation with posture.
Hyrsomallis and Goodman found only one study examining the effects of muscular endurance. Mulhearn and George (1999) attempted to examine the relationship between lower abdominal muscular endurance and lumbar lordosis. They found no significant relationship. However, the merits of the study design can be called in to question. They measured posture by classifying participants posture as either lordotic, sway back or ideal. Furthermore, reliability and validity of this or their abdominal endurance measure were not reported. Nonetheless Mulhearn and George produced showed that the association is not so strong that this depth of study was sufficient to show a relationship.
Corrective exercise specialists may expect to see stronger associations in these studies but when the multiple influences on postural control are considered the results should seem less surprising. For example the strength of muscles at different points in their range of motion, the relative muscle balance, input from mechanoreceptors, nervous system control, energy levels and even the influence of the hormonal system.
In addition 100% abdominal strength may be sufficient for one individual but if their daily demands require greater than 100% strength such as a gymnast. Someone may test as having 100% strength but they may be continually performing activities with excessive lumbar lordosis causing creep in ligaments and developing strength at a position of increased lumbar lordosis. Thus the strength and also the endurance required are relative to the individual’s demands. These complexities make devising effective studies to assess these relationships difficult but not impossible.
With this in mind how important is static posture? Some individual’s have a poor understanding of what good posture is. Dysfunctions seen in static posture aren’t always evident in dynamic movement. Clinically it is not uncommon to see a patient with poor static posture who performs movement assessments with good dynamic posture.
It’s important to consider that the underlying premise on which this discussion is based remains contentious. The effect of posture on injury risk is not well established. Studies continue to refute the very paradigm that forms the foundation of many clinicians’ treatment approaches. Nonetheless the physiology behind this reasoning is sound as with the associations between posture and muscle strength discussed above. Therefore perhaps what the literature shows us is that we need to appreciate the complexities involved in producing both injuries and static posture. Looking at posture to predict injuries will always be only weakly linked due to the multiple variables involved. Similarly, posture and muscle strength will only be weakly independently linked due to the plethora of other factors involved in producing static posture.
Thus clinically this research informs our practice. We are not looking at the whole picture if we only look to strengthen muscles to correct posture. Our programmes must consider the multitude of additional factors that influence posture if we want optimal results for our patients.
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Hrysomallis, C., and Goodman. C. 2001. A review of resistance exercise and posture realignment. J. Strength Cond. Res. 15 (3): 385–390.
Janda V., 1987. Muscles and motor control in low back pain: Assessment and management. In Twomey LT (Ed.) Physical therapy of the low back. Churchill Livingstone: New York. P. 253-278.
Kendall, F.P., McCready, E.K., and Provance, P.G., 1993. Muscles Testing and Function (4th ed.). Baltimore: Williams & Wilkins.
Mulhearn, S. and George, K., 1999. Abdominal muscle endurance and its association with posture and low back pain. Physiotherapy 85: 210–216.
Walker, M.L., Rothstein, J.M. Finucane, F.D. and Lamb, R.D., 1987. Relationships between lumbar lordosis, pelvic tilt, and abdominal muscle performance. Phys. Ther. 67:512–516.
Youdas, J.W., Garret, T.R. Harmsen, S. Suman, V.J. and Carey, J.R. 1996. Lumbar lordosis and pelvic inclination of asymptomatic adults. Phys. Ther. 76: 1066–1081.