Author ORCID Identifier

Date of Award


Degree Type


Degree Name

Master of Science (MS)


Kinesiology and Health

First Advisor

Feng Yang

Second Advisor

Jeffrey Otis

Third Advisor

Katherine Lee Hsieh


Motorized treadmills have been widely used to examine the reactive balance control of the human body after an external perturbation, like slips or trips, and develop perturbation-based interventions for preventing falls. The treadmill-induced perturbation profile depends on the belt’s duration, velocity, acceleration, and displacement. The intensity of the perturbation is affected by these interrelated factors. There is a lack of consensus regarding how to choose the perturbation intensity. One prerequisite condition to bridge this knowledge gap is to examine how the perturbation intensity affects its outcome. The purpose of this study was to quantify how the slip intensity, characterized by the belt’s peak velocity (low intensity: 0.9 m/s; medium intensity: 1.2 m/s, or high intensity: 1.8 m/s), affects the slip outcome (fall or recovery) in young adults while the slip distance is controlled. Specifically, it was hypothesized that, in comparison with a low intensity, a high slip intensity would lead to 1) a greater risk of a slip-fall and 2) a shorter recovery step latency, longer slip distance, and larger hip descent after the slip onset. Thirty-one healthy young adults aged 18 to 45 years were enrolled and randomly assigned into three groups with different peak slip speeds: low (0.9 m/s), medium (1.2 m/s), and high (1.8 m/s). After the warmup, participants stepped on the ActiveStep treadmill. Following five standing trials without slips, all subjects experienced an unexpected slip perturbation induced by the treadmill with the assigned peak slip velocity. The slip displacement was the same for all groups at 0.36 m. A motion capture system collected participants’ full-body kinematics. The slip outcome (a binary variable: fall or recovery) was determined by the hip descent after the slip onset. The faller rate was the primary outcome variable. The secondary outcome measures included the continuous measurements of the hip descent, dynamic stability, and slip distance at the instant of recovery foot liftoff, and the latency of the recovery step. The outcome measures were compared among groups using χ2 or one-way analysis of variance followed by appropriate post-hoc tests to test the hypotheses. The results overall support the hypotheses. Specifically, individuals in the high-intensity group fell significantly more than the other two groups. Additionally, they were less stable with a longer slip distance at liftoff than their peers in the lower intensity groups. This study could guide the selection of slip profiles for future studies that use perturbation as a test platform or interventional paradigm.


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