Busting other yoga myths with biomechanics

Unlike some of the improbable myths that the gals over at Smarterbodies take on in their new ebook Exposing Yoga Myths, yoga teachers could be forgiven for their misconceptions about demands placed on joints and muscles in common balancing asanas. In fact, nobody was more surprised at what is actually happening than Dr. George Salem, lead researcher for the Yoga Empowers Senior Study (YESS). Dr. Salem is Director of the Musculoskeletal Biomechanics Research Laboratory, Director of the Human Anatomy Program, directs the Exercise and Aging Biomechanics research program; and is Associate Professor in the Division of Biokinesiology & Physical Therapy at the University of Southern California.

In the study that is the subject of this post, Dr. Salem and his team used standard biomechanical analysis (joint moments of force and EMG measurements of muscle activation patterns) to examine physical demands placed on older persons, average 70 years old, performing three common variations each of Vrksasana (Tree) and Uthitta Hasta padangustasana (single leg balance).  Here’s what they discovered.

Vrksasana (tree pose)

Because it can become confusing, use this key for translating beginner, intermediate, and advanced vrksasana. You can see a visual here.

  • beginner = toes of non-stance leg touching the floor; hands on wall
  • intermediate = only stance foot touches ground; hands on wall
  • advanced = only stance foot touches ground; no wall support

They hypothesized that the beginner variation, which was done with toes on the floor and heel against the inside of the shank (lower leg) of the stance leg and using a hand on the wall for support, would be the least physically demanding . The intermediate variation, which had the entirety of the foot on the stance shank, but still holding the wall, would be more physically demanding. The advanced variation, which was classic vrksasana, with foot on shank and no wall support would be the most physically demanding. They hypothesized that the increase in physical demands would be linear. They were wrong.

Progressing

What they found was that there was a large increase in demand going from tree with the toes on the ground and wall support (beginner tree) to tree with the foot off the ground and wall support (intermediate tree). And there was not much change at all between having or not having wall support, when only the stance foot was grounded. Providing wall support doesn’t lessen demand nearly as much as lifting the toes from the mat.  This suggests that more time may be needed practicing the beginner variation before transitioning to the intermediate variation. Because older persons have diminished strength and balance, reduced joint range of motion, and a greater prevalence of osteoarthritis, some variations of what are seemingly appropriate asanas may place them at risk for musculoskeletal and neurological pain and injury. And while increased muscle loading may improve strength and endurance, excessively high joint moments of force may lead to damaging loads to joint structures and exacerbate osteoarthritis and other pathological joint issues.

Recommendation: In working with older persons in vrksasana, when they are ready to progress from the beginning variation, have them keep their toes on the floor and move away from the wall, rather than having them lift their toes while staying at the wall.

Hip Strength

Another finding was that advanced tree and intermediate tree (both with non-stance foot off the ground) were nearly identical in the physical demands of the lateral hip musculature aka abductors aka gluteus medius. Thus, there appeared to be no adaptive benefit to stepping away from the wall, when you are already balancing on one leg (toes of non-stance leg not on the ground). Thus, for students who feel safer holding onto a wall, they are gaining as much improvement in strength and endurance as those not holding the wall. Strong abductors are associated with better balance and reduced fall risk.

Recommendation: Let your students know that holding onto the wall does not undermine hip strength and will  effectively assist them in achieving better balance, decrease fear of falling and performance anxiety in class, and build confidence. 

Knee Safety

A really important finding has implications for students with knee issues. Intermediate and advanced tree pose increases loading of joint structures. Unfortunately, such loading characteristics are associated with knee osteoarthritis and joint pain, thus could exacerbate preexisting conditions. Importantly, and in contrast to commonly held conceptions, the use of a wall for support during these variations of Vrksasana does not offer protection for the knee joint.

Recommendation: For senior students with existing knee problems, suggest they stick with the beginner version of Vrksasana.

Uthitta Hasta Padangustasana (single leg balance)

Follow this key, when visualizing the beginner, intermediate, and advanced variations of padangustasana. Here is a visual.

  • beginner = extended leg supported on blocks
  • intermediate = extended leg supported on chair
  • advanced = extended leg unsupported aka supported by the strength of the student

Progressing with Props…maybe not

Again, researchers were surprised, when their hypotheses were not supported. It turns out that extending your leg onto a chair is not much of a progression over stepping onto a stack of blocks, although it appears quite a bit more demanding. (I interject that there is likely more balance anxiety for some older students to place their leg on the higher chair.) The real progression comes with the advanced variation, which uses active mobility – you holding your own leg up. What is striking to me is that while the leg may be higher on the chair, the effort is larger in the advanced variation – even though the leg is barely off the ground (see link to visual) because the student is generating internal force (muscle force) rather than relying on external force (chair) to assume the posture. It matters how you get there. It matters how you stay there.

Hamstrings

In the advanced variation, co-contraction of the hamstrings and quadriceps occurs, stiffening the joint and increasing stability, however, this increased loading may exacerbate existing knee osteoarthritis symptoms.

Recommendation: For senior students with existing knee problems, suggest they stick with the beginner or intermediate variations of Vrksasana.

Ankles

This study found Padangustasana to be an excellent posture for improving plantar flexor (think rising up onto the ball of your feet) strength and performance, which is associated with balance and postural control, gait, and fall risk in older persons. However, it’s not until students are confidently performing this one legged balance that they appreciatively load the plantar flexor muscles.  This asana is also excellent for ankle inverter strength (think sole of the foot facing in towards the midline of your body), which, like strong plantar flexor muscles, is critical for balance but also in agility and walking proficiency.

Recommendation: encourage your appropriate older students to work towards the advanced variation o Uthitta Hasta Padangustasana for improving ankle strength and agility.

Conclusions

This study’s biomechanical insights provide evidence that can be used by yoga instructors, when selecting modifications for their older students.

Here are three points to remember:

  1. Posture variations that have long been considered introductory may actually induce higher demands at some joints and planes of motion, than pose variations considered advanced.
  2. Pose variations can produce forces that are in the opposite direction of those generated during the classical variation.
  3. Use of props, such as a wall, to reduce contraindicated joint loading may have little or no effect.

As a yoga and movement teacher, my biggest take away is that there are few well-designed studies in the area of biomechanical forces and yogasana. In fact, the authors’ state that this is the first study to quantify the physical demands of yoga pose variations, using biomechanical methodologies. I will continue to seek more research like this so that I can replace time-honored ideas about what I think or what I’ve been told might be happening in yoga with what is actually happening in yoga.

The Physical Demands of the Tree (Vriksasana) and One-Leg Balance (Utthita Hasta Padangusthasana) Poses Performed by Seniors: A Biomechanical Examination. Sean S.-Y. Yu,  Man-Ying Wang,  Sachithra Samarawickrame,  Rami Hashish,  Leslie Kazadi,  Gail A. Greendale, and George J. Salem. Evidence-Based Complementary and Alternative Medicine. 2012.  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3437689/

Namaste, Michele

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