Research On Body Posture Adjustment During The Start Of Striding At Different Speeds

Background: The initiation for one single step forward could be used as a simple paradigm for the study of gait initiation,the process that involves altering the base of support and accelerating the center of mass(COM)forward,which is known to be a highly challenging task for the postural control system.It is classically used to investigate the balance control and postural adjustments of the central nervous system.The duration and amplitude parameters of the postural adjustments could co-vary with the progression velocity during step initiation for healthy young subjects.Low walking speed was proven to be one of the prominent risk factors for falls in the elderly population.It has also confirmed that slower gait initiation time can increase the risk of falls.Therefore,understanding the variation regularity of postural adjustments parameters in able-bodied subjects during step initiation influenced by gait speed is significant and valuable for the clinic to identify step or gait disorders in the elderly or populations with neurological disease,such as Parkinson's patients,to diagnose and evaluate the risk of falls and develop the rehabilitation programs.Objectives: The purpose of this study was to investigate the influence of step speed on the temporal and spatial parameters in postural adjustments.Methods: Seven healthy young adults performed the initiation of one single step tasks at two different speeds(normal speed,NS;as quickly as possible,QS).Kistler 3D force plate,Noraxon 3D accelerometer and foot pressure switch were used to collect data.The temporal and spatial parameters for the center of pressure(COP)and the COM on the anterior-posterior(AP)axis and medio-lateral(ML)axis were analyzed and compared separately under the NS and QS conditions.Results:(1)Under the QS condition,the duration of each phase in step initiation was significantly shorter than that in the NS condition,except the unloading phase duration.(2)In the APAs phase,the time to peak of COM acceleration on each axis and the time to the leftward peak of COM velocity were greatly reduced,while the time to peak of COP displacement and velocity had no obvious changes under the QS condition.(3)In the AP direction,except the peak COP displacement in swing phase,all the COP displacement parameters,COP velocity parameters,COM acceleration parameters and most of COM velocity parameters were significantly increased under the QS condition.(4)In the ML direction,there were no significant differences in all the parameters under different conditions.Only found significant enlargement in some of COP velocity parameters under the QS condition.(5)A reciprocally significant linear correlation was found between the COP displacement and COM acceleration of the APAs peaks in both directions.The progression velocity of step initiation correlated only significantly with the APAs peaks in the AP direction.Conclusions:(1)Healthy adults scaled down the duration of APAs and CPAs to achieve initiating step quickly.The regulation of APAs time was mainly depended on the reduced duration of heel-off.(2)It was possible that the central nervous system exerted an anticipatory global control of the time to peak velocity in the horizontal plane.The time to peak of COM acceleration during APAs might be an indicator to evaluate the velocity of the step initiation.(3)It was shown that the postural adjustments were directionally dependent.The components in the AP direction played a role in achieving the target speed of step initiation,while the components in the ML axis mainly contributed to maintaining body balance and postural stability.It also understood the importance of APAs in the postural control of quick initiation,and the progression velocity of step largely depended on the amplitude of APAs in the AP direction.The APAs created the initial conditions for both forward progression and ML stability.(4)Under the central control,CPAs in coordination with APAs in both directions ensured the body to achieve the safest and most efficient stepping strategy.(5)The COP displacement reciprocally linked with the COM acceleration during the APAs phase,and this relation pattern was not affected by the velocity of step initiation.