Modular control of muscle coordination patterns during various stride time and stride length combinations

• Published in: Gait & posture Vol. 94; pp. 230 - 235
• Main Authors: Kibushi, Benio, Moritani, Toshio, Kouzaki, Motoki
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 01-05-2022
• Subjects: Central nervous system; Electromyograms; Electromyography; Exercise Test; Gait - physiology; Humans; Kinematics; Male; Motor control; Muscles; Walking; Walking - physiology; Walking; Electromyograms; Motor control; Central nervous system; Kinematics
• ISSN: 0966-6362; 1879-2219
• DOI: 10.1016/j.gaitpost.2021.04.006

•Number of synergies in extreme walking patterns was adjusted.•Number of synergies in preferred and quasi-preferred walking patterns was consistent.•The modular organization for walking was adjusted to achieve extreme combinations.
Modular organization in muscular control is generally specified as synergistic muscle groups that are hierarchically organized. There are conflicting perspectives regarding modular organization for regulation of walking speeds, with regard to whether modular organization is relatively consistent across walking speeds. This conflict might arise from different stride time (time for one stride) and stride length combinations for achieving the same walking speed.
Does the regulation of the modular organization depend on stride time and stride length (stride time-length) combinations?
Ten healthy men walked at a moderate speed (nondimensional speed = 0.4) on a treadmill at five different stride time-length combinations (very short, short, preferred, long, and very long). Surface electromyograms from 16 muscles in the trunk and lower limb were recorded. The modular organization was modeled as muscle synergies, which represent groups of synchronously activated muscles. Muscle synergies were extracted using a decomposition technique. The number of synergies and their activation durations were analyzed.
The number of synergies was consistent in the preferred and quasi-preferred condition (median: 4.5 [short], 4.5 [preferred], 5 [long]), while it varied in the extreme condition (median: 4 [very short] and 6 [very long]; 0.02 ≤  p ≤ 0.09). Gait parameters (stride time, stride length, stance time, swing time, and double stance time) were significantly different for preferred and quasi-preferred conditions (p <  0.03).
Our results provide additional insights on the flexibility of modular control during walking, namely that the number of synergies or activations are fine-tuned even within one walking speed. Our finding implies that a variety of walking patterns can be achieved by consistent synergies except for extreme walking patterns.