Ultrasound-derived changes in thickness of human ankle plantar flexor muscles during walking and running are not homogeneous along the muscle mid-belly region

E F Hodson-Tole,A K M Lai

doi:10.1038/s41598-019-51510-4

Abstract

Skeletal muscle thickness is a valuable indicator of several aspects of a muscle’s functional capabilities. We used computational analysis of ultrasound images, recorded from 10 humans walking and running at a range of speeds (0.7–5.0 m s−1), to quantify interactions in thickness change between three ankle plantar flexor muscles (soleus, medial and lateral gastrocnemius) and quantify thickness changes at multiple muscle sites within each image. Statistical analysis of thickness change as a function of stride cycle (1d statistical parametric mapping) revealed significant differences between soleus and both gastrocnemii across the whole stride cycle as they bulged within the shared anatomical space. Within each muscle, changes in thickness differed between measurement sites but not locomotor condition. For some of the stride, thickness measures taken from the distal-mid image region represented the mean muscle thickness, which may therefore be a reliable region for these measures. Assumptions that muscle thickness is constant during a task, often made in musculoskeletal models, do not hold for the muscles and locomotor conditions studied here and researchers should not assume that a single thickness measure, from one point of the stride cycle or a static image, represents muscle thickness during dynamic movements.

Highlights

Skeletal muscle thickness is a valuable indicator of several aspects of a muscle’s functional capabilities
A general pattern of increased thickness over the first 50% of the stride cycle, followed by rapid thinning of the muscle was seen across all gait conditions
Can a single measure of muscle thickness be considered representative of a whole muscle region? The initial aim of the presented work was to determine whether a single, ultrasound based, measure of muscle thickness, taken from the mid-region of the image, can be considered representative of the portion of muscle imaged over the course of a stride cycle

Summary

Introduction

Skeletal muscle thickness is a valuable indicator of several aspects of a muscle’s functional capabilities. In studies of human skeletal muscles, ultrasound imaging provides a well-tolerated, minimally invasive means of visualising the muscles that can be used across a wide range of motor tasks (e.g. posture[6], isokinetic dynamometer tasks[7] and locomotion[8]) Such studies focus on the behaviour of an individual muscle and, where measures of thickness are taken, they are typically from the mid-region of the recorded images and simplify the aponeurosis to being a straight line (e.g. a line between two points defined at each end of the image). The purpose of the work presented here is to: (i) identify whether a single measure of muscle thickness, in the central portion of the image, can be considered representative of a whole muscle region and; (ii) quantify changes in thickness of synergistic muscles sharing an anatomical compartment (i.e. the calf region of the human lower leg) during different locomotor tasks. We report thickness changes in human soleus (SO), medial and lateral heads of gastrocnemius (MG, LG) muscles, determined from active shape model based analysis of ultrasound images recorded during walking and running at a range of steady-state speeds

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Discussion

Conclusion