Resting Muscle Shear Modulus Measured With Ultrasound Shear-Wave Elastography as an Alternative Tool to Assess Muscle Fatigue in Humans

Abstract

The aim of this study was to investigate the time course of the resting vastus lateralis (VL) muscle shear elastic modulus (μ) measured with ultrasound shear-wave elastography during repetition of isometric maximal voluntary contractions (MVCs) of the knee extensors (KE). Fifteen well-trained young males repeated 60 5-s isometric MVCs. Evoked electrical stimulations and the VLμ were measured every ten MVCs at rest. The resting VLμ significantly decreased (−34.7 ± 6.7%; P < 0.001) by the end of the fatigue protocol. There was also a 38.4 ± 12.6 % decrease in MVC after exercise ( P < 0.001). The potentiated doublet and single twitch torque amplitudes and properties were significantly modified by the end of exercise ( P < 0.001). This study shows the time course of the resting VLμ during the repetition of maximal voluntary fatiguing exercise of the KE muscles. The decrease of the resting VLμ could directly affect the force transmission capabilities accounting for peripheral fatigue.

Changes in the Viscoelastic Properties of the Vastus Lateralis Muscle With Fatigue

“…Participants performed an intermittent voluntary fatigue protocol consisting of 6 sets × 10 repetitions of 5-s maximal voluntary isometric contractions (MVICs) of the KE muscles and 5-s passive recovery periods between repetitions with 10 s of rest between sets ( Figure 1A). The number of contractions was chosen to generate a high level of voluntary strength loss and peripheral fatigue, as previously demonstrated (Siracusa et al, 2019). Participants were not informed of the criterion for the end of the task (60 MVCs) but had visual feedback of torque output during the exercise.…”

“…VL muscle was chosen because previous studies (Alkner et al, 2000;Place et al, 2007) showed that this muscle is representative of the muscle quadriceps. Moreover, studies showing decreases in muscle stiffness by assessing aponeurosis or muscle tendon junction displacements or by SWE after repeated isometric contractions were made exclusively in the VL muscle (Kubo et al, 2001a;Morel et al, 2019;Siracusa et al, 2019), allowing comparisons with the present study.…”

“…A 5V TTL signal was triggered at the generation of each SWE image using a PowerLab system (16/30-ML880/P, ADInstruments, Bella Vista, Australia) connected to the ultrasound device to synchronize the SWE measurements with the torque values. During the ramped contractions, the cutoff was set at 50% MVIC, corresponding to the upper limit, after which the elastography measurement reaches saturation for up to 25% of the ROI (saturation = 16.329 m/s or 800 kPa), as observed in a previous study (Siracusa et al, 2019). An active muscle stiffness index was then calculated from a linear regression between the mean VL µ values and KE absolute torque (slope), which is independent of the level of force.…”

“…In vivo characterization of the viscoelastic mechanical properties of skeletal muscle [e.g., stiffness or shear modulus (µ) and shear viscosity (η)] has long been a great interest (Gennisson et al, 2010;Lacourpaille et al, 2012Lacourpaille et al, , 2014Andonian et al, 2016;Davis et al, 2018;Rasool et al, 2018). Recent evidence suggests that the assessment of subtle modifications of muscle stiffness may be helpful in identifying the early development of muscle fatigue (Andonian et al, 2016;Siracusa et al, 2019), damage (Lacourpaille et al, 2014), or disease (Rasool et al, 2018). We recently demonstrated (Siracusa et al, 2019) that the resting vastus lateralis µ (VL µ), assessed by shear-wave elastography (SWE), was reduced (−34.7 ± 6.7%) after a series of voluntary isometric contractions of the knee extensor (KE) muscles.…”

“…Recent evidence suggests that the assessment of subtle modifications of muscle stiffness may be helpful in identifying the early development of muscle fatigue (Andonian et al, 2016;Siracusa et al, 2019), damage (Lacourpaille et al, 2014), or disease (Rasool et al, 2018). We recently demonstrated (Siracusa et al, 2019) that the resting vastus lateralis µ (VL µ), assessed by shear-wave elastography (SWE), was reduced (−34.7 ± 6.7%) after a series of voluntary isometric contractions of the knee extensor (KE) muscles. Moreover, such reduced muscle stiffness was accompanied by a decrease in the voluntary torque and modification of the mechanical properties of a single twitch (e.g., reduced peak torque, longer electromechanical delay and contraction time, and reduced rate of force development) of the KE after exercise.…”