Vf 13 5

For the purpose of standardization, right femoral vein measurements were used in the study. The FV was visualized with B-mode US, 2–5 cm below the level of the inguinal ligament, just above the inguinal canal, from where the femoral artery was best palpated, without applying any pressure that could affect the diameter of the FV [10 (link)]. Next, FV diameter variation during the respiratory cycle [maximum FV diameter (FVD_max), minimum FV diameter (FVD_min)] was measured in the transverse view using a high-frequency linear array transducer [(VF 13–5; 4.1–12.1 MHz), Siemens, USA] on M-mode, and images were saved for reevaluation after the procedure. Using the values obtained, the FV collapsibility index (FV-Ci) was calculated with the following formula: FV-Ci = [(FVD_max–FVD_min)/(FVD_max)] × 100 [10 (link)] (Figure 1).

Muscle architecture was analysed using Real-time B-mode ultrasonography with a linear-array probe (VF13-5, Siemens ACUSON P500, Erlangen, Germany). Muscle thickness (MT, in mm), fascicle length (L_f, in mm) and pennation angle (in degrees) of the VL muscle were determined at 50% of the femur length (McPhee et al. 2018 (link)), while the cyclist was seated with the knee and hip at 90° of flexion. All ultrasound scanning and image analysis (Image J, v1.8.0_112; National Institutes of Health, Bethesda, MA) was completed by the same investigator. All architectural parameters were given as the average of three measurements in the image. MT was defined as the shortest distance between the superficial and deep aponeuroses. L_f was calculated using the extrapolation method (Brennan et al. 2017 (link)) when necessary. The pennation angle was defined as the angle between the deep aponeurosis and the fascicles. The intra-rater coefficient of variance (CV) for all the measurements was below 10% (CV MT = 1%, CV L_f = 6%, CV pennation angle = 9%).