Declines Of Lateral Balance In Old People And Effects Of Regular Tai Chi Exercise On The Declines

Background and Purpose:Age-related declines in balance may be accentuated in the lateral direction. However the underlying mechanism is still unknown. Tai Chi (TC), as a traditional Chinese martial art, seems to have positive impact on lateral stability. The purpose of the study was to explore the mechanism of age-related declines in lateral balance and observe the effect of regular TC exercise on the declines.Research methods:Total 57 men were divided into three groups, including young adults (n=15), elderly long term Tai Chi practitioners (TC group, n=14), elderly long term joggers (jogging group, n=14), and elderly sedentary controls (sedentary group, n=14). Force platform was used to evaluate static posture control in different standing postures. The related parameters of center of pressure (COP) included area, displacement, and velocity in lateral and forward-backward direction. The postural response to unexpected lateral perturbation was evaluated using kinematical, kinetics, and EMG parameters. The EMG parameters included muscle latency, time to peak amplitude, contribution rate of different muscles. The kinematical parameters included maximum displacement of trunk. The kinetic parameters were similar with static COP related parameters.Results:1. Compare between elderly sedentary controls and young adults.(1) Static postural control in elderly sedentary controls significant lower: Under Single-Leg with Eyes Open (SLO), elderly sedentary controls'COP range significantly increased in all directions. Under Tandem Stance with Eyes Closed (TSC), exclude the total velocity all COP parameters significantly increased in eldly sedentary controls. Under Tandem Stance with Eyes Open (TSO), the elderly sedentary controls'lateral range and total area significantly increased. Besides, compare TSO with TSC in the same group, the young adults group's lateral COP parameters show significantly increased when their eyes closed. When elderly sedentary controls closed their eyes, their COP parameters almost show significantly increased. The results suggest that the elderly are more dependent on visual factors in static postural control.(2) Lateral disturbance:The onset latency of older group in peroneus longus muscle, anterior tibial, gastrocnemius, gluteus medius, semitendinosus, semitendinosus and deltoid muscle neuromuscular response show significantly decline.The time to peak of EMG amplitude of older group in peroneus longus muscle, anterior tibial, gastrocnemius, rectus femoris, gluteus medius muscle delayed.Compared the contribution rate of same muscle to analysis the main body segment in different postural phase. The young adults group mobilizes ankle, hip and trunk to participate in postural control rapidly and coordinate. There is no movement in older group'joints in the first postural phase. In second phase gastrocnemius increased. In third phase ankle and trunk increased.There is no difference in maximum trunk displacement between different directions, but older group's standard deviation of trunk displacement increased. It cue that the elderly showed a worse dynamic postural stability.The elderly's COP ML range, lateral amplitude RMS and AP range increased, but AP amplitude RMS and AP velocity decreased.2. Compare among sedentary group, jogging group and TC group(1)Under SLO,static posture stability of sedentary group significantly worse than TC group and jogging group, there is no difference between TC group and jogging group. Under TSO, static posture stability of TC group si better than sedentary group, but there is no difference between jogging and sedentary group. Under the most difficult TSC, static postural stability of TC group is not only better than sedentary group, but also better than jogging group. (2) Lateral disturbance:In left disturbance, the onset latency of TC group in anterior tibial, ercctor spinae, semitendinosus and ercctor spinae is shorter than sedentary group, and the ercctor spinae also shorter than jogging group;The onset latency of jogging group in anterior tibial and semitendinosus is shorter than sedentary group. In right disturbance, the onset latency of TC group in anterior tibial, peroneus longus and ercctor spinae is shorter than sedentary group. These changes not only shorter than sedentary group, but also shorter than jogging group. The onset latency of jogging group in anterior tibial and ercctor spinae is shorter than sedentary group.Compared with sedentary grop, the time to peak of EMG amplitude of TC group in gastrocnemius, rectus femoris, ercctor spinae muscle reduced. The time to peak of EMG amplitude of TC group in peroneus longus and semitendinosus also reduce when compare with jogging group.Three older groups accept different postural strategy in lateral dynamic disturbance. Contribution rate of gluteus medius in sedentary group play an important role in their postural strategy. The jogging group's anterior tibial show highere contribution rate. Moreover the TC group's ercctor spinae contribution rate is particularly prominent among three groups.The Tai Chi practice can reduce trunk displacement under dynamic disturbance, but jogging's effect was not obvious. The TC group also shows best dynamic postural stability under dynamic disturbance.The sedentary group's COP total velocity, AP amplitude RMS are smaller than TC group, and total velocity, ML velocity RMS and AP velocity RMS are also smaller than jogging group.The conclusion of the study:1. Compared with young adults, the static posture stability of sedentary group significantly declined, especially when posture control difficulties increased. The sedentary group show poor dynamic postural stability in lateral disturbance.2. Declines of lateral postural control in old people:(1) The muscle of limb, hip and trunk in sedentary group show delay onset latency, and declined in the contraction efficiency, so weakened postural control.(2) To deal disturbance, the sedentary group, not only segment adjust late, and over-reliance on a single segment. They show delay and stiff postural control.(3) In lateral disturbance, the sedentary group's reverse angle in transverse plane declined may weaken lateral postural control.3. The regularly exercise can improve older static and dynamic posture control. However different method of its training effect of exercise is different, Tai Chi can significantly improve the postural stability of elderly.4. Effects of regular Tai Chi exercise on these declines:Tai Chi practice can shorten onset latency and improve muscle contraction efficiency, especially in trunk muscle.The postural strategy of TC group closer to young adults in lateral disturbance.The Tai Chi practitioners improve the changes in postural to maintain lateral dynamic balance.