Modular control during incline and level walking in humans

Abstract

The neuromuscular control of human movement can be described by a set of muscle synergies factorized from myoelectric signals. There is some evidence that the selection, activation and flexible combination of these basic activation patterns are of a neural origin. We investigated the muscle synergies during incline and level walking to evaluate changes in the modular organization of neuromuscular control related to changes in the mechanical demands. Our results revealed five fundamental (not further factorizable) synergies for both walking conditions but with different frequencies of appearance of the respective synergies during incline compared with level walking. Low similarities across conditions were observed in the timing of the activation patterns (motor primitives) and the weightings of the muscles within the respective elements (motor modules) for the synergies associated with the touchdown, mid-stance and early push-off phase. The changes in neuromuscular control could be attributed to changes in the mechanical demands in support, propulsion and medio-lateral stabilization of the body during incline compared with level walking. Our findings provide further evidence that the central nervous system flexibly uses a consistent set of neural control elements with a flexible temporal recruitment and modifications of the relative muscle weightings within each element to provide stable locomotion under varying mechanical demands during walking.

Lower complexity of motor primitives ensures robust control of high-speed human locomotion

“…Another outcome of this study was the different contribution of the GM muscle for the 315 participants of G1 and G2. In G1, as found in the past [10,33,35,38,52], the GM and GL were crucial contributors to the propulsion synergy, together with the SO and PL. In G2, though, the contribution of the GM shifted to the weight acceptance phase at both maximal and submaximal speeds.…”

“…The fourth and last synergy reflected the late swing and the landing preparation, highlighting the relevant influence of knee flexors and foot dorsiflexors. As showed in the past for other locomotion conditions 110 [10,33,35,38,52], not all the participants exhibited all the four fundamental synergies at all speeds; in particular, 27% and 30% of the total synergies were classified as combined in walking and running, respectively. We reported the detailed numbers in Table 1.…”

“…The initial angle determines the position of the centre 20 of mass, which reaches its highest (in walking) and lowest (in running) point in the middle of the 265 stance phase [59]. This may physically constrain the production of forward forces in walking from the plantarflexors, which are major contributors in this phase [10,35,52,60], since only after half stance there can be propulsion, while in running it can happen earlier [2]. This could explain the physiological constraint to the recruitment timing of those muscles responsible for the weight acceptance (mostly knee extensors) and propulsion (mostly plantarflexors) phase.…”

Motor control of an insect leg during level and incline walking

“…From insects to mammals, leg muscle activity is thought to be controlled via neural circuits in the central nervous system that integrate descending inputs from the brain and afferent inputs from the leg (Hooper and Büschges, 2017;Orlovsky et al, 1999;Pearson, 1995;Prochazka, 1996). One possibility is that descending inputs mediate distinct motor programs for inclines, for example by modifying muscle synergies (Janshen et al, 2017;Smith et al, 1998). Another possibility is that afferent inputs from leg proprioceptors adjust leg muscle activity on a step-by-step basis.…”

Hindlimb muscle function in turtles: is novel skeletal design correlated with novel muscle function?

“…In this context, it is notable that pleurodire turtles, including E. subglobosa, have remained a primarily aquatic lineage throughout their evolutionary history, whereas cryptodires have radiated onto land multiple independent times (Joyce and Gauthier, 2004;Bonin et al, 2006). In addition to being affected by differences in muscle attachment, muscle function also can be influenced by the external environment (Gillis and Blob, 2001;Nishikawa et al, 2007;Foster and Higham, 2017;Janshen et al, 2017), and animals often exhibit differences in both the timing (Gillis and Biewener, 2000;Blob et al, 2008) and intensity (Biewener and Gillis, 1999;Gillis and Biewener, 2000) of muscle use during locomotion in water and on land. In addition to structural variations, such as differences in muscle moment arms, such dynamic modulations of muscle activity are likely an important component of motor control that allows animals to use the same structures to move through different environments (Gillis, 1998;Earhart and Stein, 2000;Rivera et al, 2010;Ashley-Ross et al, 2014;Perlman and Ashley-Ross, 2016).…”