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The effect of selected lower limb muscle activities on a level of imbalance in reaction on anterior-posterior ground perturbation

Wodarski Piotr, Chmura Marta, Szlęzak Michał, Gruszka Grzegorz, Romanek Justyna, Jurkojć Jacek

Acta of Bioengineering and Biomechanics

2022

Vol. 24, no. 3

135--146

We investigated whether an increase in muscular tone induced by the information about imminent posture destabilisation brings a positive result and prevents such destabilisation. Methods: We measured forward and backwards movements of 38 participates (27 females and 11 males, aged 23 (SD 2.6)) on the treadmill (forward and backward movements). All participants were subjected to three test condition trials (Tr): 1) subject did not know the nature and time of perturbation (Tr1); 2) subject knew the nature of perturbation but did not know time (Tr2); 3) both the time and nature of perturbation were known precisely (Tr3). The tests resulted in the determination of muscular activity connected with a postural adjustment as well as values of pressure exerted by the forefoot on the ground, and the angle of flexion in the knee joint. Results: In terms of postural adjustments, it was possible to observe statistically significant differences in muscular activity between Tr1 and Tr2 with reference to Tr3. No statistically significant differences were identified in all phases regarding values of forefoot pressure and those concerning the angle of flexion in the knee joint. An increase in the muscle tone before perturbation was correlated with the displacement and the velocity of the COP after perturbation. Conclusions: The results obtained indicate that knowledge of the expected time of perturbation is responsible for postural adjustment. Furthermore, muscle tone resulting from an adjustment of perturbation and responsible for the stiffening of lower limbs triggered greater displacement of the COP after perturbation.

Study of postural adjustments for humanoidal helpmates

Villalobos J., Zielińska T.

Journal of Automation Mobile Robotics and Intelligent Systems

2017

Vol. 11, No. 4

15--25

Humanoid robots and humans look alike, and therefore are expected to adjust their posture in a similar way. We analysed a set of human static postures that should be considered for humanoids acting as caretakers. A dynamic situation was studied to learn how humanoids can react in a dynamical way. Human data were obtained with a professional motion capture system and anthropometric tables. The static postures were studied using a segmented human body model, but for motion analysis the single and double pendulums with moving masses were also employed. For robot motion synthesis we need to know the relation between the posture and the postural stability. We have shown that the positions of mass centres of the pendulum segments (which match the human body point masses) are crucial for postural stabilization. The Zero-Moment Point criterion was applied for the dynamic case. The static analysis demonstrates that there are some common features of the postures. The dynamic analysis indicated that both pendulums are good models of human body motion, and are useful for humanoid motion synthesis. In humanoids, it is easier to apply results represented by inverted pendulums than postural models represented by stick diagrams. This is because humanoids and humans do not obviously share the same mass distribution and sizes (proportions) of all body segments. Moreover our descriptions indicate where to locate the supporting leg/legs in single and double support, which in general, is missing in inverted pendulum models discussed in the literature. The paper’s aim is to deepen the knowledge about the adjustment of human postures for the purpose of robotics.