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Gait initiation during stepping down a curb: anticipatory and reactive postural adjustments

Grant number: 18/03146-0
Support Opportunities:Scholarships abroad - Research Internship - Doctorate
Effective date (Start): May 13, 2018
Effective date (End): March 12, 2019
Field of knowledge:Health Sciences - Physical Education
Principal Investigator:Fabio Augusto Barbieri
Grantee:Lucas Simieli
Supervisor: Jaap Hendrik van Dieen
Host Institution: Faculdade de Ciências (FC). Universidade Estadual Paulista (UNESP). Campus de Bauru. Bauru , SP, Brazil
Research place: University Amsterdam (VU), Netherlands  


Anticipatory postural adjustments (APAs) and reactive postural control (RPC) are important for postural control when gait is initiated. Both are essential for preventing falls, either by enhancing or by recovering stability. While APAs occur in feedforward manner prior to the main motor action, RPC occurs after a perturbation of stability, requiring online adjustments. The aim of the present study is to investigate APAs and RPC during gait initiation during expected and unexpected stepping down from a curb in young and older adults. Our hypotheses are that older people will present less stable APAs and less effective RPCs during the first landing after stepping down unexpectedly. Specifically, APAs in older people will show smaller margins of stability and RPC in older people will show greater forward linear and angular momentum, compared to the young group. Thirty people will participate in this study: 15 young people (from 20 to 35 years old) and 15 older people (over 65 years old). The participants will be invited to perform 30 trials in three conditions: gait initiation without stepping down (20 trials), gait initiation with expected stepping down (5 trials) and gait initiation with unexpected stepping down (5 trials). For the unexpected condition, the ground in front of the participant will collapse just before heel contact. For all spatial-temporal parameters an optical system with 3x3 cameras will be used to record full-body kinematics. Two force plates will record ground reaction forces in the start position and at the first foot positioning. APAs will be determined as any adjustments/alteration in center of pressure that occur before apparent foot movement until the center of pressure is in the most posterior and lateral position relative to the stance leg. The RPC phase will start when the leading limb contacts the second force plate until the trailing limb contacts the ground again. We will characterize the APA and RPC by the total distance traveled and average velocity of the center of pressure in the anteroposterior and mediolateral directions. We will assess stability during the APA, first and second step by calculating the extrapolated center of mass and its margins of stability relative to the center of pressure. To assess effectiveness of RPC, linear and angular momenta changes during landing of the leading leg will be related to those during push-off of the trailing leg. To further characterize RPC, joint powers in ankles, knees and hips, as well as the work produced around these joints will be calculated. For minimum margins of stability, joint powers and angular and linear momenta we will perform MANOVAs with a factor for the groups (Young people x Older people) and conditions (Gait initiation without descending a curb x Gait initiation descending a curb x Gait initiation with unexpected descending a curb). Tukey univariate tests will be performed to identify differences when the MANOVA reveals significant interactions. If the normality and homogeneity assumptions are not met, appropriate transformations will be applied. (AU)

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