In locomotion, humans have to deal with irregularities in the ground. When they encounter uneven terrain with changes in vertical height, they adjust the geometry of their legs. Recent investigations have shown that the preactivation of the gastrocnemius muscle (GM) correlates with the ankle angle at touchdown, but it is as of yet unclear why these adjustments were achieved by the GM and not by the preactivation of the tibialis anterior (TA). To examine the differences between TA regulation and GM regulation regarding (1) ankle angle adjustment and (2) joint stiffness, we used a three-segment musculoskeletal model with two antagonistic muscles (GM, TA). During the GM regulation, the ankle angle was adjusted from 121° to 109° (dorsiflexion) by a 41% decrease in the GM activation. During the TA regulation, the activation of TA must be increased by about 52%. In addition, we found that the ankle stiffness was most sensitive to changes in activation of the GM and decreased by about 20% while adjusting the angle. In contrast, the ankle stiffness remains similar when using TA regulation. Thus, the GM regulation is more adequate for adjustment in the ankle joint, enabling sufficient regulation of angle and stiffness.
Roy Müller, Tobias Siebert and Reinhard Blickhan
Daniel Hamacher, Dennis Hamacher, Roy Müller, Lutz Schega and Astrid Zech
The aim of the current study was to evaluate the effect of a cognitive dual task on minimum toe clearance (MTC) variability while walking. In a randomized cross-over design, gait kinematics of 25 older (70 ± 6 years) and 45 younger adults (25 ± 2 years) were captured during normal walking and dual-task walking. Variability of stride time, stride length, and MTC were calculated. Differences between normal versus dual-task walking were assessed using Wilcoxon tests. Compared with normal walking, dual-task walking caused an increase in stride time variability (older adults: p < .001 and younger adults: p < .001), while the variability of MTC decreased (older adults: p = .032 and younger adults: p = .012). MTC seems to be a task-relevant gait parameter that is controlled with high priority to preserve its variability under challenging conditions.