Several studies have shown that Tai Chi improves balance and prevents falls in older adults. But what is it about Tai Chi that improves postural stability in elderly people? To try and answer that question, one study focused on gait initiation (GI). In the study, all the Tai Chi participants showed significant improvements in center of pressure (COP) trajectories in gait initiation. There was also a significant increase in the A-P and M-L COP displacements observed in the Tai Chi participants.
Gait initiation is the transitional movement between standing and walking. Older adults usually fall during movement transition. Consequently, the mechanisms involved in gait initiation are appropriate to study to determine the differences between stable and unstable persons and the effects of Tai Chi on these mechanisms.
Gait initiation involves a stereotypical movement of muscles in the lower extremities. This creates moments of force about the ankles and hip, which rotate the body. The center of pressure (COP) in the saggital plane is controlled by muscles at the ankle. (The saggital plane is an imaginary line which represents the planes of motion that the human body is capable of moving through. It is vertical and runs from the front to back and divides the body into the left and right side. Bodily movements in the saggital plane involve flexion and extension).
Any changes in the translation of COP are due to a response of the central nervous system to movement in the whole body center of mass. Therefore, COP is used as an indicator of balance and postural control.
“Less forceful generation of COP displacement in the anteroposterior (A-P and mediolateral (M-L) directions has been observed in older adults.” There is also a theory that another cause of the less forceful generation of COP displacement is dysfunctional habits (like poor posture). For these reasons, the study examined the difference between the translation of COP in gait initiation in older adults before and after Tai Chi training to see if Tai Chi produces any improvement.
“In the initiation of gait, the muscles of the lower extremities are activated stereotypically and create moments of force about the ankles and hip, which rotate the body. Initially, there is an inhibition of the tonic soleus (SOL), which is active during the quiet stance, followed by the onset of tibialis anterior (TA) activity of both the swing and stance limbs.”
However, this pattern is not observed in older adults as often as it is in healthy, younger adults. In the case of older adults, sometimes the inhibition of SOL did not take place before the TA was activated. That may explain why a reduced backward movement of COP was observed in older adults. Therefore, it is possible that increased COP displacement in the A-P direction in older adults may result if the stereotypical pattern of SOL inhibition taking place before TA activity is restored. In this study, positive changes in COP displacement were observed in Tai Chi participants.
“Increased M-L COP displacement is likely to be the result of improved coordination of the hip abductor and adductor muscles. In the initiation of gait, the stance-side momentum is generated by the swing limb hip abductors that propel COP laterally toward the swing limb. Therefore, muscle activities at the ankle and hip tend to propel the COM forward and toward the intended stance limb.”
In sum, Tai Chi is thought to prevent falls by improving the ability to generate mobility via a greater COP shift in the A-P and ML directions as well as in the maintenance of balance and lateral stability when initiating gait.