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

Tatsuya Kato,Kimitaka Nakazawa,Takanori Kokubun,Naotsugu Kaneko,Motonori Hoshino,Hirofumi Kobayashi,Hikaru Yokoyama

doi:10.1038/s41598-021-98022-8

Abstract

Underwater walking is one of the most common hydrotherapeutic exercises. Therefore, understanding muscular control during underwater walking is important for optimizing training regimens. The effects of the water environment on walking are mainly related to the hydrostatic and hydrodynamic theories of buoyancy and drag force. To date, muscular control during underwater walking has been investigated at the individual muscle level. However, it is recognized that the human nervous system modularly controls multiple muscles through muscle synergies, which are sets of muscles that work together. We found that the same set of muscle synergies was shared between the two walking tasks. However, some task-dependent modulation was found in the activation combination across muscles and temporal activation patterns of the muscle synergies. The results suggest that the human nervous system modulates activation of lower-limb muscles during water walking by finely tuning basic locomotor muscle synergies that are used during land walking to meet the biomechanical requirements for walking in the water environment.

Highlights

Underwater walking is one of the most common hydrotherapeutic exercises
Evident water environment-dependent changes in the EMG patterns based on visual inspection in the examples were as follows: 1) decreased amplitude in the gluteus medius (Gmed) and tensor fasciae latae (TFL), 2) an activation timing shift from after the foot contact to before the foot contact in the rectus femoris (RF), and 3) decreased amplitude modulation in the medial gastrocnemius (MG)
Group means of correlation coefficients of the EMG envelopes between the conditions showed moderate correlations in most of the muscles (r = 0.40–0.69), while RF and tibialis anterior (TA) showed low correlation values (r = 0.10 and 0.36, respectively)

Summary

Introduction

Underwater walking is one of the most common hydrotherapeutic exercises. understanding muscular control during underwater walking is important for optimizing training regimens. The effects of the water environment on walking are mainly related to the hydrostatic and hydrodynamic theories of buoyancy and drag force. From a biomechanical point of view, the effects of the water environment on walking movement are mainly related to the hydrostatic and hydrodynamic theories of buoyancy and drag force. 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]. The details of modular control of the muscle activation patterns during water walking, which are different from those during land walking[7,8,9,10,12,14], remains unclear. Investigation of the similarity of the muscle synergies between land and water walking may provide useful information for the neurorehabilitation of walking

Results

Discussion

Conclusion