Pelvic mobility
Pelvic morphology (shape) differs across the globe, with mean population differences found in different gene pool groups. For example;
- Acetabular inclination angle in Indians, on average, is 37° [1]
- While the normal value in European literature is taken as 45° [2]
Reductionist anatomical and biomechanical reasoning may suggest that this is significant in a yoga context. The argument is that as cup angles of inclination reaches 45 degrees or more, this may be one possible factor that could impact internal and external rotation, potentially becoming apparent with hip flexion greater than 60 degrees.
This in theory would result in on-average differences between students with Western European ancestries and Indian ancestries, in both:
- How long it may take to achieve certain poses, and;
- The type of stimulus required to achieve certain poses.
Poses implicated here include, Padmasana, Baddha Konasana, leg behind the head poses, and advanced poses like Mulabandhasana and Kandasana.
Firstly, why does this variation exist?
There is ample evidence that populations (both human and mammalian) living in different climates tend to have different body proportions, with cold‐adapted populations having relatively larger and stockier bodies, and populations in hot climates having smaller or more elongated bodies with relatively longer limbs (Weinstein, 2005; Tilkens et al., 2007; Weaver and Hublin, 2009, Betti et al., 2012, 2015).
This pattern is widespread in endotherm animals, with closely related species displaying larger body sizes and shorter extremities in colder environments, and it is often referred to as Bergmann's (1847) Rule (for body size) and Allen's (1877) Rule (for body and limb proportions).
After the expansion out of Africa and the colonisation of high latitude regions, it has been suggested that natural selection favoured more robust and stocky bodies with a lower surface‐to‐volume ratio, which helped maintain internal body temperature in cold climates.
Differential climatic adaptation might therefore have contributed in generating modern population differences in body proportions, body size, limb robusticity, and even pelvic shape (Trinkaus, 1981; Ruff, 1991, 1994; Holliday and Falsetti, 1995; Pearson, 2000; Stock, 2006; Weaver and Hublin, 2009).
Kurki (2013a) compared nine populations from various continents, and found a relationship between latitude and pelvic shape, whereby high‐latitude populations tend to have a transversally wider midplane and outlet and an inlet which is less deep antero‐posteriorly than mid‐ and low‐latitude populations. Betti et al. (2014) and Weaver (2002) found a significant relationship between temperature and the 3D shape of the ilium and of the whole pelvis, suggesting that both pelvic and canal shape have been partially shaped by local climatic adaptations, possibly through the effect of natural selection favouring thermally efficient body sizes and proportions.
Additionally, random accumulation of differences due to genetic drift and differential migration is an ever‐occurring process and can potentially explain a portion of phenotypic variation between human populations.
Implications for the existence of yoga asana traditions of South India practiced by Westerners:
Postures from Krishnamacharya’s South Indian yoga system, such Kandasana, Dwi Pada Sirsasana, or Mulabandhasana, may be far more readily accessible for certain body types, with a probabilistic tendency to favour equatorial genetic ancestry.
For example, Karnataka in India (Krishnamacharya’s region of birth) is an equatorial region which has a yearly average temperature of 32 degrees the climate is very warm to hot all year round, and is incidentally the origin of most modern forms of physical yoga).
Avoiding population average fallacies
Firstly, we have to be aware that these findings relating to pelvic morphology are population based averages, and genetic variance often has more in-group variability than between-group variability. Which is to say these are simply averages, and tell you nothing about any specific individual, as there is great variance either side of the mean distribution (think a bell curve).
Avoiding biomechanical extrapolation
While pelvic morphology, in theory, may offer a compelling reason to correlate differences we observe in individual mobility, this has an unreliable historical track record. For example, acromial morphology (scapular shape), was thought to be a predictor of shoulder pain, as a “hooked” or type 3 acromion appears to reduce subacromial space and increase impingement of tendons. However, now there is ample evidence that subacromial impingement is an invalid and unreliable measure and diagnosis, and there is no evidence that the shape of the acromion influences shoulder function.
Avoiding reductionism
Many factors play a role in joint mobility, and the relative flexibility of the muscles and soft tissue around a joint is one such factor. This muscle and tissue elasticity is modulated by the nervous and immune systems, so inputs into the system (stress, negative beliefs about movement, lack of sleep, training and exercise history and lifestyle habits) potentially play a greater role than morphology alone.
Avoiding nocebic interpretations
Images of these varied pelvic shapes do not represent what living, adapting tissue with a muscular and nervous system complete with consciousness look like. The danger is placing arbitrary limitations on ourselves based on beliefs about a pelvic morphology, when in fact no one can truly know their full strength or mobility potential without assessing it empirically, and working on all the modifiable variables outside of morphology.
Understanding environmental and cultural inputs
Cultural norms relating to sitting on the floor, as opposed to sitting on chairs potentially has a large effect size on hip mobility, particularly during the formative years of childhood and adolescence. This may, arguably, play a greater role than body type in determining ones baseline hip range of motion.
Floor culture is still prevalent throughout much of India, and many parts of Asia, and there is ample anecdotal evidence (the author included) that shifting to sitting cross legged and squatting on the floor instead of sitting on chairs can slowly restore lost mobility around the hips and pelvis. (I have also heard of anecdotal reports of the converse being true, which is highly plausible). For more on this see this blog here
For Teachers and Students
An awareness of all the inputs that affect hip range of motion may help teachers Individualise yoga sequences for different physical morphology, different lifestyles, while recognising self-limiting beliefs, educating regarding the variability in time frames that it may take to achieve certain poses, and how these vary from person to person.
We could summarise this as not assuming one-size-fits-all teaching pedagogy, and that;
Population data does not generalise to any specific individual
Everyone is different, and poses and sequences (as well as mobility drills outside of asana practice) should be adapted to cater for these differences
One can never truly know their full capability without long term practice and dedication
Depending on your own unique circumstances (nature and nurture) achieving the pelvic mobility required for these techniques will require differing amounts of time.
For example when I first started yoga my the musculature around my hips was very inflexible.
The following pictures are from 2010 (I began practice in 2008)
For additional reference, my genetic profile is from North Western Europe. Sweden has an average temperature of 2.9 degrees Celsius.
Training tips to increase mobility
Weighted mobility, using agonist and antagonist contractions, with repetitions and long holds:. For example in baddha konasana below. It took me many years to get the knees on the floor.
Active lowering into front splits, side splits and pigeon
In addition to many more drills available, these type of mobility exercises can help one achieve the mobility required for the asanas, mudras and bandhas central to Hatha Yoga.
REFERENCES:
1. Singh, S., Kumar, S., Rohilla, S., & Maini, L. (2014). Functional anthropometric measurements of Indian pelvis. Journal of clinical orthopaedics and trauma, 5(2), 79–83. https://doi.org/10.1016/j.jcot.2014.05.001
2. Kummer FJ, Shah S, Iyer S, DiCesare PE. The effect of acetabular cup orientations on limiting hip rotation. J Arthroplasty. 1999 Jun;14(4):509-13. doi: 10.1016/s0883-5403(99)90110-9. PMID: 10428235.
3. Betti, L. (2017), Human Variation in Pelvic Shape and the Effects of Climate and Past Population History. Anat. Rec., 300: 687-697. https://doi.org/10.1002/ar.23542