The Applicability of Shear Wave Elastography to Assess Myotendinous Stiffness of Lower Limbs during an Incremental Isometric Strength Test

The aim of the study was to describe the applicability of shear wave elastography to assess muscular and tendinous stiffness of the lower limbs during an incremental isometric strength test and to differentiate the stiffness evolution between superficial and deep muscle regions. Dominant rectus femoris and patellar tendons of 30 physically active people (28.3 +/- 9.2 years, 173.2 +/- 7.7 cm, 76.2 +/- 12.6 kg) were measured in different isometric strength conditions (relaxed muscle, and at 10%, 20%, 30%, 40%, 50% and 60% of maximal voluntary contraction (MVC)). The percentage of success was >85% at all muscle contraction intensities for rectus femoris muscles but only in a relaxed condition for patellar tendons. Rectus femoris stiffness significantly increased compared to the relaxed condition from 30% to 60% MVC (p <= 0.011) in superficial muscle regions, and from 10% to 60% MVC (p <= 0.002) in deep muscle regions. Deep muscle regions showed higher stiffness values than superficial muscle regions at 30% MVC (51.46 +/- 38.17 vs. 31.83 +/- 17.05 kPa; p = 0.019), 40% MVC (75.21 +/- 42.27 vs. 51.25 +/- 28.90 kPa; p = 0.018), 50% MCV (85.34 +/- 45.05 vs. 61.16 +/- 37.03 kPa; p = 0.034) and 60% MVC (109.29 +/- 40.04 vs. 76.67 +/- 36.07 kPa; p = 0.002). Rectus femoris stiffness increased during the incremental isometric contraction test, and inter-region differences were found at 30% MVC.

Automated summary

The aim of this study was to assess the applicability of shear wave elastography in evaluating the stiffness of muscles and tendons in the lower limbs during an incremental isometric strength test, and to differentiate the stiffness changes between superficial and deep muscle regions. The results showed that the stiffness values in deep muscle regions were higher than those in superficial muscle regions, and the stiffness of the rectus femoris muscle increased gradually during the incremental isometric strength test.