Table 1.
Demographic and training profile data.
Fig 1.
a) US image obtained in axial plane showing the different areas of interest within the quadriceps muscle: the RF, rectus femoris (red); the VL, vastus lateralis (pink); and the VM, vastus medialis (green). b) Elastographic data collection: 5 circular 5 mm-diameter ROIs (Q boxes) were manually placed within each squared SWE box by the same radiologist, who was experienced in performing musculoskeletal ultrasound. For example, this picture shows the positions of the Q boxes for the RF. The operator was blinded to the quantitative shear modulus data. c), d), E) and f) are in-plane fiber-aligned US images of the RF, VM, VL, respectively. The orange-dotted square ROIs correspond to the three sequential positions of the SWE-boxes used for the SWE measurements. Thus, at each investigation time, 9 SWE boxes were saved (3 for the RF, 3 for the VM and 3 for the VL). Note the absence of gas bubbles within the thick gel layer. The X- and Y-scales are, respectively, the in-plane and depth distances in centimeters.
Fig 2.
Measurement protocol and subject positioning.
An articulated arm ensures that no contact occurs between the transducer and the thigh. Acoustic coupling is ensured using a home-designed silicon pool conforming to the shape of the leg that is filled with bubble-free acoustic gel. All subjects were placed in the supine position using a feet holder to ensure that the quadriceps femoris muscle remained at rest. To maximize inter-day reliability and hasten re-positioning, 4 indelible skin lines were traced during the Pre session (with a waterproof marker). The first line extended across the thigh and was drawn 15 cm above the upper edge of the patella, perpendicular to the patella-ASIS (anterior superior iliac spine) axis. The remaining three lines were drawn parallel to the longitudinal axis of the center of each of the three muscle heads (RF, VM, VL). Per the PLOS ONE policy regarding papers including identifying or potentially identifying, information, each subject was informed of the terms of the PLOS open-access (CC-BY) license and provided permission for the publication of these details under the terms of the license.
Table 2.
Relative (intraclass coefficient) and absolute (standard error of measurement) shear modulus (μ) reliability.
Table 3.
Longitudinal shear modulus (μ) and shear wave velocity (Vs) variations over time.
Fig 3.
Change in muscle head stiffness (shear modulus).
Changes observed in the three muscle heads (RF, VM and VL) at the three measurement times (Mid, Finish, and Recovery) are expressed as percentages of their baseline values, or their Pre values. The error bars denote the 95% confidence interval, and the boxes denote the 25th–75th percentiles with the median. The asterisks indicate that the changes from baseline are significant based on the statistical analysis of the raw data, which is presented in the Results section.
Table 4.
Longitudinal variations in blood biomarkers throughout the ultra-marathon race.
Table 5.
Percent changes in biomarker levels and shear modulus values between the Finish and Pre sessions (% change Finish/Pre).
Fig 4.
Edematous and architectural thigh muscle changes at the Finish assessment.
US images of the quadriceps femoris muscle, which were obtained in the axial plane during the Pre session (a) and the Finish session (b). Note the edematous thickening of the skin and the muscle fascia in the image obtained during the Finish session.