Intra-limb and muscular coordination during walking on slopes

Abstract

Purpose Intra-limb and muscular coordination during gait are the result of the organisation of the neuromuscular system, which have been widely studied on a flat terrain. Environmental factors, such as the inclination of the terrain, is a challenge for the postural control system to maintain balance. Therefore, we hypothesised that the central nervous system flexibly modifies its control strategies during locomotion on slopes. Methods Ten subjects walked on an inclined treadmill at different slopes (from − 9° to + 9°) and speeds (from 0.56 to 2.22 m s −1 ). Intra-limb coordination was investigated via the Continuous Relative Phase, whereas muscular coordination was investigated by decomposing the coordinated muscle activation profiles into Basic Activation Patterns. Results A greater stride to stride variability of kinematics was observed during walking on slopes, as compared to walking on the level. On positive slopes, the stride period and width present a greater variability without modification of the timepattern of the muscular activation and of the variability of intersegmental coordination. On negative slopes, the stride width is larger, the variability of the stride period and of the inter-segmental coordination is greater and the basic activation patterns become broader, especially at slow speeds. Conclusion Our findings suggest that the control strategy of downhill walking corresponds to a more conservative gait pattern, which could be adopted to lower the risk of falling at the cost of a greater energy consumption. In uphill walking, where metabolic demands are high, the strategy adopted may be planned to minimise energy expenditure. Keywords Coordination • Neuromuscular control • Basic activation pattern • Continuous relative phase Abbreviations CRP Continuous relative phase GRF Ground reaction force EMG Records of the electrical activity produced by skeletal muscles TO Toe off COP Centre of pressure FC Foot contact F x , F y , F z Lateral, fore-aft and vertical component of the GRF d y , d x Lateral and fore-aft position of the COP ω i , θ i Lower-limb segment angular velocity and position φ iN Phase angle ϕ iN CRP angle MARP Mean absolute relative phase DP Deviation phase of the CRP FWHM Full width at half maximum CI Co-activation index NNMF Non-negative matrix factorisation P, W Basic activation patterns and associated weighting components VAF Variability accounted for

Basic locomotor muscle synergies used in land walking are finely tuned during underwater walking

“…At the same speed, a similar set of lower limb muscle synergies was extracted during slope walking 23 , 24 , walking with Nordic poles 30 , and walking on an uneven surface 41 as that during normal walking. Similar to these previous studies, our results also showed the similarity of the extracted muscle synergies between land and water walking at the same speed.…”

“…Regarding the task specificity of locomotor muscle synergies, although whether the number of muscle synergies during locomotion changes depending on speed is still controversial, the temporal activation coefficients are modulated depending on speed 15 , 19 – 22 . Other studies have reported that similar muscle synergies are used for walking on different slopes, but the activation combination across muscles and the temporal activation coefficients are modulated depending on the conditions 23 , 24 . To date, no study has investigated the muscle synergies used during underwater walking.…”

“…Therefore, we extracted muscle synergies from recorded EMG signals during land walking and water walking to examine modular neuromuscular control for walking in a water environment. Based on the two different adaptation patterns of muscle synergies to changes in walking conditions mentioned above 15 , 23 , we formulated the following two hypotheses for the adaptation of muscle synergies to the water environment: (1) muscle synergies specific to water walking are recruited, and (2) muscle synergies similar to those for land walking are used during water walking, but the activation combination across muscles and the temporal activation coefficients in the synergies are modulated.…”

Common kinematic synergies of various human locomotor behaviours

“…In this context, motor modules at different levels (often called synergies) have been revealed, thereby providing support for the modular control hypothesis [10]. For example, studies on the neural control of muscles show that a few muscle synergies sufficiently describe various muscle activation patterns in human locomotion [4,13,14]. Studies on kinematics find that the joint motions of the lower limb can be effectively explained by a few kinematic synergies in some typical human movements (e.g.…”

Neuromuscular Age-Related Adjustment of Gait When Moving Upwards and Downwards

“…In healthy young adults, locomotor movements can be accommodated to various situations, such as walking slopes ( Hong et al, 2014a , b ; Dewolf et al, 2017 ) or stepping on stairs ( McFadyen and Winter, 1988 ; Silverman et al, 2014 ), by means of appropriate changes in the intersegmental coordination and muscle activations ( Dewolf et al, 2018 , 2020b ). During walking uphill and upstairs, the height of the center of mass of the body (COM) must be increased each step whereas it must be decreased during walking downhill and downstairs.…”