How Was This Research Conducted?
The study took place in a studio in Austin, TX. 45 people were divided up into 3 groups, each consisting of 13 females and 2 males.
Their ages ranged from 18-60 years old.
Each group got into headstand a different way. The three entries into headstand were:
- Both legs straight at the same time (SE: symmetrical extended)
- Both legs bent at the same time (SF: symmetrical flexed) and
- Both legs bent one at a time (AF: asymmetrical flexed).
All of the groups had the same foundation of the pose with the forearms on the floor, hands clasped around the back of the skull,
and the crown of the head touching the floor. Everyone did the pose 3 times for a duration of 5 breaths with a 2 minute rest in between.
They analyzed the kinetics and kinematics of all three ways of getting into the pose. They assessed peak forces on the head,
the loading rates, center of pressure (COP) and cervical alignment.
They measured these attributes during three phases of each headstand: the entry, stability and exit.
The part of the mat where the practitioner put his or her head was touching the force plate; however, the section
under the arms was not. It would have been interesting to see how much force was exerted in the forearms for comparison.
Peak forces and loading rates
Upon entry, the SE leg position (both legs straight at the same time) showed the least amount of loads in the head and neck. SE had less amounts of force during the entry and stability phases of the pose. I found it interesting that the SE stability portion (when static) also showed less load than the others. This was the slowest way to come into the pose which showed that moving slowly while applying force to the head resulted in the least amount of force. This means that speed plays a role in the amount of force that is produced.
Those who came up with one leg at a time came up the quickest and loaded the head more rapidly than the other two techniques. This resulted in the highest measured loads on the head and neck.
Across the board, maximum force occurred in the stability phase of headstand and maximum loading rate occurred upon entry. This suggests that for the duration of the pose, weight is transferred from the arms to the head and neck.
What kinds of loads are we talking about?
Forces on the head were measured in percentages of practitioners total body weight. The average maximum measured force on the head was 40-48% of total body weight, which means they hold nearly half of their body weight on their head and neck. Maximum loads upon entry were calculated in newtons. Maximum loads during entry and stability were above 300N on average for the AF group and below 250N for the SE group (~15 lbs difference). Fifty-one percent of the subjects in this study experienced maximum forces above 300N in the neck and head.
These levels of force may be of concern when considering previous literature which shows fracture at those levels. It’s important to know that that research was done on cadavers that were dropped on their heads, not living subjects. A cadaver being dropped on the head is very different than a person coming into headstand. Force is distributed to muscles and soft tissues in the body when coming into headstand.
Center of Pressure
The center of pressure was evaluated at the crown of the head. With all three techniques, there was more side to side maneuvering upon entry into and exit out of the pose. They mention that this introduces the potential for lateral (side) fractures nerve root avulsion (McElhaney and Myers, 1993).
As mentioned before, maximum force occurred in the stability phase of headstand and maximum loading rate occurred upon entry. They measured neck angles during those points of max loading (entry) and max force (stability). During the point of max loading rate, neck extension increased. Neck angle change at the point of max force was not significant. The SE option showed more neutral cervical conditions upon loading. Those who entered one leg at a time were the least able to maintain neutral cervical curve.
They reference a study that showed that cervical failure was four times greater with extension and compression than with flexion (Carter et al., 2002). However, it’s important to know that this study was done on a section of cadaver spine. Human living tissue behaves very differently. So just because it happened on the cadaver does not mean it will happen to a living person experiencing the same compression and extension in the cervical spine.
What Does This Mean For Teachers?
The entry and exit techniques are one of the few variables the practitioner can control. Entering headstand with straight legs together may reduce the load and the rate of change of that load on the head. This happens to be a more challenging way to get into the pose for many people. If someone is able to get into the pose that way and is trying to minimize forces on the cervical spine then that could be the preferred entry into the pose.
Avoiding the pose all together may be preferred, especially if the practitioner has disc degeneration, spondylolisthesis, osteoporosis or osteopenia (all very common). Why risk loading the neck?
All of the subjects in this study were regular practitioners, familiar with and capable of doing headstand. We know this because in order to be in the study they had to be able to hold the pose for 5 breaths. It’s important to consider that newbies may be more vulnerable to injury in headstand.
I personally have chosen to exclude headstand from my group classes and will only teach it individually to students who want to do it and who don’t have contraindicated conditions (as far as they know). I made this decision well before I read this study. This study helped me feel more justified in that decision.
But it’s also important for us as yoga teachers not to instill a sense of fear in people who want to do headstand. As said above, even though 48% of body weight is placed on the head, this does not mean that it will break the neck. Loads are distributed to the muscles and soft tissues too not just the bones. The data from the 300N study is from cadavers which is very different from human beings doing headstand.
As far as I know this is the first study that assessed peak forces tolerated by the head and neck when coming into headstand. For future studies, it would also be useful to see what the forces are throughout the duration of the pose (especially since some like to hold it for long periods of time) and how much distribution of force there is between the forearms, head and neck.
The data recorded pertaining to exiting the pose was not consistent because subjects exited the pose however they wanted to.
As usual, more research is needed. It would be useful for studies to examine factors that affect the force on the neck, such as weight, height, age, sex, and body proportions. What about people with longer or shorter humerus bones? How would that affect force distribution?