Year of Publication

2021

Date of Thesis

12-2021

Document Type

Thesis

Degree Name

Master of Science

Department

Exercise and Sport Sciences

Abstract

Balance control is an essential skill for human activities. Gait initiation is a common daily movement involved in walking, stepping, and reaching tasks (Halliday et al., 1998). In the gait initiation process, both static and dynamic balance control ability are being tested. Anticipatory postural adjustments (APAs) are the body’s preparation before voluntary movement to maintain balance control. APAs allow for better performance in the subsequent voluntary movement by making a successful transition from static to dynamic balance control (Gribble et al., 2012). The star excursion balance test (SEBT) is a popular functional movement test for balance control. The SEBT involves multi-directional balance control and reaching initiation providing an ideal test for studying APAs in multidirectional reaching movements. Since the study of APAs in multidirectional reaching is lacking in published research, the purpose of this study is to explore the relationship between SEBT reaching directions, APA patterns, center of force (COF) directional displacement, and reaching performance. The difference between reaching directions and limb is also examined.

Ten participants (age: 19.33 ± 1.16 years; height: 169.25 ± 12.88 cm; body mass: 71.18 ± 16.00 kg) performed three complete SEBT trials in each of the anterior (ANT), posteromedial (PM), and posterolateral (PL) directions with both left and right limb stance. The results showed a consistent COF trajectory pattern in each direction and common features across all directions during the S1 APA phase. The S1 APA phase is the 1st phase of the APAs during which the COF shifts posteriorly from the center towards the reaching limb as a countermovement to the impending reach. In the S2 phase, the 2nd phase of the APAs, the COF consistently shifted with mediolateral movement from the reaching limb to the stance limb. The only difference in S2 phase across directions was an anterior component that appeared in the ANT reach but was absent in the PM and PL reaches. Objective results revealed significant differences in reaching distance (RD) between directions (F (2,18) = 48.674, p< .001, partial η2=.844) but not limbs (F (1,9) =1.168, p = 0.308, partial η2=.115). RD in PM was larger than PL and larger than ANT reach. Despite differences in RD, similar COF trajectory patterns were observed across reach directions. There was insignificant difference in anteroposterior displacement (DyS1) between directions (F (2,18) =2.050, p = .158, partial η2=.186) and limbs (F (2,18) = 0.114, p = .743, partial η2=.013). There was significant difference in mediolateral displacement (DxS1) between limbs (F (2,18) = 52.494, p < .001, partial η2 = .854) because of the reaches occurring in opposite directions, left and right, but the magnitude of movement was insignificant (F (2,18) = 1.113, p = .319, partial η2 = .110). The difference in mediolateral displacement (DxS1) between reach directions was insignificant (F (2,18) = 2.652, p = .098, partial η2 = .228). A smaller COF displacement in the reaching tasks of this study compared to the stepping tasks studied by Inaba et al. (2020) show that a reduced magnitude of destabilization is necessary for controlling momentum during the APAs of a reaching task which requires the COF to stay within the base of support.

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