# Morphological and Mechanical Symmetry of the Quadriceps and Hamstrings in Athletes
## 2 Materials and Methods
### Data Collection  
Anthropometric data were measured according to the International Society for the Advancement of Kinnthropometry [33]. The body mass (kg) of the athletes was assessed using a portable electronic scale (Model PCS 180, Super Crown, Shangqiu, Henan, China) with a resolution of 100 g. Height was assessed using a tape (Single Fiber Tape Measure, Sanny, Sao Bernardo do Campo, Sao Paulo, Brazil) with a resolution of 1 mm. Athletes should wear light clothing and be barefoot for these measurements.  
Initially, the subjects rested for 10 min, lying on a stretcher in supine position, with their lower limbs extended so that the body fluids could stabilize, avoiding interference in the images. After 10 min, the CSA and EI of the quadriceps and hamstrings muscles were assessed using a B-mode ultrasound system (ACUSON S2000; Siemens Healthcare, Mountain View, CA, USA) with a 9L4 linear array probe (40 mm, 8.0 MHz frequency), and the configuration for image acquisition was maintained the same for all subjects. Ultrasound images were captured in extended field of view (EFOV) mode by the same person, positioning the transducers at 50% of the proximal-distal length of the femur [34], transversely to the belly muscles. Two EFOV images were collected for each muscle group, in both limbs, resulting in four images per muscle group and eight images per subject.  
\begin{table}
\begin{tabular}{c c} \hline \hline  & **Athletes**\(\sigma\)**(16)** \\ \hline Training (years) & 8.25 \(\pm\) 5.06 \\ Age (years) & 22.1 \(\pm\) 2.2 \\ Height (cm) & 176.6 \(\pm\) 13.6 \\ Body Mass (kg) & 73.1 \(\pm\) 13.1 \\ Body Mass Index (kg/m\({}^{2}\)) & 23.4 \(\pm\) 2.8 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Descriptive characteristics of the competitive team sports athletes.  
Double-sided tape (3M\({}^{\text{TM}}\)) was adhered transversely to the quadriceps or hamstring skin to serve as a side-rail for the probe to slide over the gel in the anterior and posterior regions of the thigh. The transducer was covered with a water-soluble transmission gel (to provide acoustic contact without depressing the dermal surface) on its distal surface, which was applied to the skin to obtain the images. A fixed configuration was used for all subjects in order to quantify the gray scale of the images with the following configurations of the ultrasound system (Frequency: 8.0 MHz; 80 mm image depth; 0 dB overall gain and time gain compensation in the neutral position).  
After the ultrasonography protocol, data were collected using an isokinetic dynamometer (BIODEX, System 4 Pro\({}^{\text{TM}}\), Biodex Medical Systems, New York, NY, USA), which was calibrated according to the manufacturer's instructions. The subjects were seated at the dynamometer chair, adjusted to maintain 85\({}^{\circ}\) of hip joint flexion, and were attached with Velcro straps to provide stability during testing. The rotation axis of the dynamometer was aligned with the rotation axis of the tested knee joint (lateral femoral condyle). The lever arm was positioned to lower limb level, and a fixed-length pad was positioned 1 cm above the lateral malleolus.  
The warm-up consisted of 20 submaximal knee extension-flexions at 120\({}^{\circ}\)/s. After a two-minute interval, subjects performed five maximal concentric contractions at 60\({}^{\circ}\)/s and 300\({}^{\circ}\)/s; extension and flexion were measured at in one movement sequence. The interval between each contraction adopted was two minutes. Before the beginning of each evaluation protocol, the evaluated velocities were randomized in order to avoid the effects of muscle fatigue on the torque production capacity. All assessments were performed on both DO and ND lower limbs, and the same two evaluators were responsible for verbal encouragement to ensure maximal effort from the athlete and protocol explanations.