The Effects Of Tai Chi On Postural Control Ability During Stair Walking Under Dual-Task Condition Among Older Women

Objectives:It’s reported that about one third of the elderly had at least one fall per year,and 62% of them are female.Stair walking is one of the main external factorsleading to falls.Oncefalling,it will cause serious injury or even death.Decreased postural control is the primary internal factor in the falls.Posture control during stair walking is not only the result of muscle control,but also the regulation of brain cognitive resources.Conducting dual tasks will distract attention and affect the distribution of cognitive resources,And different types of dual tasks have different effects on motor control.With the increasing age,the fuction of musculoskeletal and neural system declined for the elderly,which will further increase the risk of falling during stair walking.Therefore,the purpose of this study is to investigate the characteristics of posture control during stair walking among the elderly women under dual-task condition.Tai Chi,as the quintessence of Chinese culture,is an mind-body aerobic exercise,whichhas a good effect on preventing falls.It’s unknown whether this special exercise can improve the posture control of older women with the interference of dual tasks.Therefore,the second purpose of this study is to investigate the effects of Tai Chi exercise on posture control ability of elderly females during stairs walking under dual task condition.Methods:To investigate the effects of Tai Chi exercise on posture control ability of older women under dual task condition,this study completed the following three experiments: Experiment 1,test-retset reliability of posture control ability during stair walking under dual task condition,to verify the reliability of evaluation index with the interferences of dual tasks while walking stairs.Experiment 2,the posture control ability of older women during stair walking under dual task condition,to investigate the gait,body stability and mechanical characteristics of lower extremity,and to find out the variation characteristics of posture control ability among the older women.Experiment 3,the effects of Tai Chi on posture control ability during stair walking under dual task condition among older women.This study,compared to the results of posture control ability acquired from experiment 2 during dual task conndition,aimed to explore whether the Tai Chi exercise benefit the improvement of posture control ability.The specific experimental methods are as follows:Experiment1,15 older female subjects were required to perform stair walking in 4 conditions: single task(no interference),cognitive task(any three digits minus three),motor task(carrying ar cup of water),and combinedtask(cognitive task and motor task simultaneously).Kinematic and kinetic data were collected usingVICON infrared motion capture System and Kistler force mesurement System,and re-test experiment was conducted a week later.Kinematic and kinetic parameters were evaluated for consistency with intra consistency coefficient(ICC)and correlation coefficient(r).Experiment 2,20 elderly and 20 young subjects were instructed to perfoeme stair walking in the four tasks condition mentioned above.Kistler force mesurement system and VICON infrared motion capture system were used to collect kinematic and kinetic data under different conditions.Gait parameters,stability control parameters and mechanical parameters of lower limbs were analysed using two-way MANCOVA to explore the walking posture control characteristics in the elderly females during stairs walking under dual task condition.Experiment 3,20 eldely female participants were recuited in Tai Chi group,brisk walking group and Control group(the elderly group in experiment 2)respectively,and all participants were instructed to perform stairs walking under four task conditions,and the kinematic and kinetic data were collected simultaneously.Gait parameters,stability control parameters and mechanical parameters of lower limbs were analysed using two-way MANCOVA to explore the effects of Tai Chi on posture control ability during stairs walking under dual task condition among the elderly females.The gait parameters,stability control parameters and lower limb mechanics parameters of three groups were compared to explore the influence of Tai Chiquan exercise on the elderly’s walking posture control ability in dual-task mode.Results:Experiment 1: In the four taskconditions,ICC value of the kinematic parameters while ascending stairs was 0.705-0.967,indicating fair to excellent reliability the value of r is 0.700-0.990,indicating weak correlation to high correlation;theICC value ofkinetic parameters while ascending stairs was 0.705-0.979,indicating good and excellent reliability,the value of r was 0.613-0.960,indicating significant correlation and high correlation;ICC value of kinematic parameters while descending stairs was 0.705-0.964,indicatingfair to excellent reliability.,the value of r was 0.701-0.935,indicating a moderate correlation to high correlation;ICC value of kinetic parameters while descending stairs ranged from 0.639 to 0.963,indicating good and excellent reliability,ssthe value of r ranged from 0.619 to 0.930,indicating a significant correlation and high correlation.Experiment 2: Results of gait measurement showed that older participants had significantly lower walking velocity,cadence and increased gait period under combined task condition while ascending and descending stairs compared to single task.The results of body stability measurement showed that compared tosingle task,both the clearence and movement range of ankle of older participants were significantly reduced,while the angle of ankle joint was significantly increased under combined task condition,but the distance between center of mass(COM)and center of pressure(COP)was significantly larger under cognitive or motor dual task condition during stair ascending and descending.The results of mechanical measurement for lower limbs showed that under combined task condition,the peak value of power in hip,knee and ankle joint decreased significantly during stair ascending in the elderly group,while the moment and peak value of power in both knee and ankle joint were significantly decreased during stair descending.Compared to the single task,the walking velocity and cadence were significantly decreased for young participants under the other conditions,while there was no significant difference in body stability and mechanical index of lower limbs.Under the same task conditions,there was poor significance in gait parameters,body stability and mechanical index of lower limbs for older group.Experiment 3: Results of gait measurementshowed that the stride width of the Tai Chi group was significantly larger than that of the control group,and the double supporting phase was significantly longer than that of the brisk walking group and the control group.Compared tothe single task,the walking velocity and cadence of the Tai Chi group were decreased,while the stride width and double supporting phase were increased.The results of body stability measurement showed that compared to the brisk walking group and the control group,the Tai Chi group had a significantly shorter distance between COM and COP under the four conditions.And Tai Chi participants had a significantly larger clearence and movement range of ankle,while the angle of ankle joint was significantly small under motor and combined task conditions;Under three dual task conditions,the distance between COM and COP,movement range of ankle or the angle of ankle joint was significantly small for Tai Chi group,while the clearence was significantly larger under combined task condition.The results of mechanical measurement for lower limbs showed that the peak value of knee extension moment,toe flexion moment and positive work of hip were all significantly larger for Tai Chi group under three dual task conditions compared to the brisk walking group and the control group,while under single or cognitive task condition,the peak value of positive work in knee and ankle jointwere significantly larger during stair ascending.Under motor and combined task condition,Tai Chi group showed a significantly larger peak value of toe flexion moment and a significantly smaller loading rate.Tai Chi group also showed significantly larger peak value of negtive power in hip joint,and second peak value of negtive power in knnee joint and peak value of both positive and negtive power in ankle joint were all significantly larger under all above conditions.Conclusion: Under both single task and dual task condition,the retest reliability and correlation of the kinematic and kinetic parameters while ascending stairs and descending stairs was better,and the test-retest reliability is higher;both aging and dual-task can lead to the decline of the walking posture control ability during stairs walking,and the posture control ability of the elderly women decreased with the increase of difficulty of dual tasks.Compared with the brisk walking group and the control group,the elderly female prcticing Tai Chi mainly adopt the gait adjustment strategies of reducing the wlking speed,increasing the stride width and prolonging the double supporting phase when interfered by dual tasks,and through the musculoskeletal system adjustment of increasing the moment and power of the knee and ankle joint of the supporting leg,increasing and performing motion adjustment of increasing the motor range and angle of ankle joint of the swing leg,which can maintain the stability of COP and COP and improve the stability control while stepping over the stairs,and thus reduce the risk of falling;As a kind of physical and mental exercise,Tai Chi can not only improve the body function,but also improve the cognitive function of the brain.It may be the reason that Tai Chi can significantly enhance the body stability compared to brisk walking exercise.So we recommend that the elderly take long-term Tai ChiTai Chi exercise regularly to prevent the fall during stair walking.