Changes in the balance in the course of treadmill or over-ground movements can result in falling or injuries. It is therefore important to adequately understand stability during locomotion. Margin of stability is a parameter that has been introduced recently that is implemented to determine the dynamic stability in terms base of support and extrapolated center of mass in the mediolateral and anteroposterior orientations.
A number of research works have also shown that margin of stability can be used to analyze dynamic stability during motion and have reported differences in dynamic stability when there is a change in locomotion speed, perturbation intensity, and step length and width. In addition, researchers have focused on dynamic stability under self-paced speed conditions. This is where a runner runs at a selected speed. They have also focused on fixed speed, where the runner is subject to a predetermined speed.
Features of dynamic stability have also been evaluated by comparing fixed speed and self-paced speed conditions in similar locomotion setups. Some researchers have found that speed differences between self-paced and fixed speed conditions affected the step length, step, frequency, and step width, which subsequently affected the mediolateral margin of stability.
Sayup Kim, Jongryun Roh and Joonho Hyeong at Korea Institute of Industrial Technology in collaboration with Giltae Yang at Chonbuk National University and Youngho Kim at Yonsei University in South Korea used the margin of stability index of dynamic stability to compared self-paced and fixed speed conditions using the non-motorized curved treadmill. By altering the size and curvature of the treadmill, the authors were able to identify locomotion condition that were appropriate for realizing high dynamic stability during the non-motorized curved treadmill. Their research work is published in International Journal of Precision Engineering and Manufacturing.
The research team measure the locomotion of the subjects using 8 motion cameras as well as 25 reflection markers at 60Hz sampling speed. They defined a single step as the distance from the point of the heel strike of the left foot to that of the right foot. The authors, from the beginning of locomotion, selected the most stable interval between 20 and 40 s composed of twenty steps as the analysis interval. The researchers generated the full body segments from the 25 markers attached on the body of the subject. The results recorded were used to compute the location of the center of mass.
The authors found the interaction effects to be between the speed and curvature radius. They confirmed the differences between each curvature radius and speed, and found considerable differences between self-paced and fixed speed conditions. As per the experimental outcomes, under the fixed and self-paced speed conditions, the dynamic stability was observed to increase with the curvature radius during fast and slow walking.
Under the self-paced condition, the researchers observed that as the curvature radius increased, the margin of stability in the anteroposterior direction decreased during running. On the contrary, under the fixed speed condition, they observed no distinctive trend. At most speeds and curvature radii, considerable differences were observed between the fixed and self-paced speed conditions.
The outcomes on their study indicates that while exercising on the non-motorized curved treadmill, the fixed speed and the self-paced conditions at varying curvature radii as well as speeds can affect the dynamic stability. These results can therefore be used to verify exercise capacity improvement and rehabilitation exercise effects.
Sayup Kim, Jongryun Roh, Joonho Hyeong, Giltae Yang, and Youngho Kim. Dynamic Stability on Nonmotorized Curved Treadmill: Self-Paced Speed versus Fixed Speed. International Journal of Precision Engineering and Manufacturing Vol. 18, No. 6, pp. 887-893.
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