I have been an advocate for Tai Chi (taiji quan) for at least as long as I’ve been a Physical Therapist, and have previously written about the benefits Tai Chi can bring to physical therapists and physical therapy. In this series, I aim to share some of the ways I’ve been able to apply the principles and practice of Tai Chi to my therapy skills, an in doing so enhance my patients’ care.
What is ‘Weight Shift’ and Why is it Important?
In basic terms, weight shift is our ability to move our center of mass (CoM) – our ‘weight’ – around our body in order to maintain – or disrupt – our balance. Think of your CoM like a pendulum or a plumb-bob; when you stand with perfect balance, your CoM sits right in the middle of your base of support (ie: the area around your feet). Once you start moving, your ‘pendulum’ moves as well, generally in the direction you are moving. We do this all the time – in fact, if we couldn’t move our CoM, we couldn’t move at all.
An easy way to understand weight shift is to attempt to stand on one leg. To do this, you have to move your CoM – or ‘swing your pendulum’ – over your supporting leg so you can lift the other leg off the ground. If you don’t, you won’t be able to lift your leg, or if you do, you body will want to fall over to that side. You can try this for yourself to see how it feels (just make sure you do it by a table or counter top so you’ve got something to grab onto if you need it!).
Being able to weight shift not only facilitates movement, it can help prevent unwanted or undesirable movement, for example, falling. Falling is a major contributor to injury and death amongst many populations: in the US, falling is considered to be leading cause of both fatal and non-fatal injuries. Physical therapists spend a great deal of time trying to both prevent falls in patients, and help patients recover from falls. Teaching patients to understand both how their CoM affects their balance, and how to shift their weight appropriately for safe movement, is critical to achieving functional movement and stability. However, in many patients the ability to weight shift is impaired either because of disease (eg: neuropathy, arthritis, vertigo) and injury (eg: stroke, spinal and nerve injuries), and regaining the ability to control weight shift can be very difficult.
Weight shift is one of a number of fundamental skills Tai Chi training can improve or enhance. Almost every movement in any form from start to finish involves a gradual, controlled transfer of weight in coronal, sagittal, and transverse planes of movement. In order to perform the forms correctly, Tai Chi practitioners control the displacement of their CoM in all planes through slow, precise movements. In most instances, the CoM remains ideally located within the practitioner’s base of support, making it easy to maintain balance. This is evident even when the practitioner is performing ‘unbalanced’ movements, such as standing on one leg.
A classic example of this is the technique known as mao xing, or ‘cat walking’. In mao xing, the Tai Chi practitioner shifts weight into one leg while stepping forward with the other. The stepping leg has no weight in it right up to the point the heel makes contact with the ground. The practitioner completes the step by gradually transferring weight from the supporting leg to the stepping leg, involving a shift from side-to-side and back-to-front. As the stepping leg is loaded it becomes the supporting leg, eventually freeing up the other leg to take another step forward. (Note: this is a very simplistic description of mao xing and there is a lot more involved in it, however this illustrates the basic concept. I recommend trying Tai Chi to better understand mao xing)
One main difference between mao xing and regular walking is the way weight shift is controlled. In regular walking, the CoM is displaced forward of the body, and the body’s reaction is to shift weight to one leg while stepping through with the other. Keeping the CoM displaced forwards and alternately repeating the sequence facilitates movement while preventing a fall forwards. In effect, walking is a repeatedly controlled fall. (Note: again, this is an overly simple description of walking, however is biomechanically accurate) Mao xing on the other hand, keeps the CoM positioned ideally within a person’s base of support at all times, even when one leg is not supported on the ground. Consider this in terms of a person who has an impaired ability to weight shift, such as someone who has a dense hemiplegia following a stroke. Which method of walking would you consider safest to have them perform?
Applying Tai Chi to Physical Therapy: Stroke and Femoral Nerve Injury Examples
Recently I was able to apply the principles of mao xing to improve the mobility of two patients who had difficultly with weight shift: a middle-aged male with a dense left hemiplegia following a stroke, and an elderly female with the inability to maintain knee extension following an injury to her femoral nerve. Neither patient was able to support weight on their affected side and both were consequently such a high risk of falling they could only mobilize in a wheelchair. Therapy included exercises to encourage weight shift and improve the ability to bear weight over the affected side, however in both instances progress was slow and their was little retention between therapy sessions.
Using the principles of mao xing, I had both patients practice stepping into a lunge stance with their affected side, then returning to a neutral standing position. Patients practiced the gradual loading and unloading of the affected side, first supported and then with standby assistance as their skill improved. In both cases, within the completion of 2 sets of 10 repetitions there was an observed improvement in the patient’s understanding and ability to shift weight to the affected side, and in maintaining standing balance. With successive therapy sessions and in conjunction with other exercises, both patients advanced their ability to weight shift to the point where they were able to stand and mobilize with an appropriate aid. The male with the hemiplegia was ultimately able to mobilize with a cane independently. The female with the femoral nerve injury has so far progressed to be able to mobilize with a standard frame under supervision.
This is, at best, observational evidence of a specific application of Tai Chi principles to physical therapy, and weight shift is only one aspect of maintaining balance. However, it does support the increasing body of evidence-based research advocating Tai Chi as a means of improving balance and mobility, and in my opinion, is worth further investigation as an adjunct to physical therapy.