# Relationship Between Front Crawl Trunk Incline and Lower Limbs' Biomechanics in Non-Expert Swimmers
## 2 Materials and Methods
### Study Design and Data Collection  
A cross-sectional research design was applied, with the swimmers having one testing session in a 25 m indoor pool with a water temperature of 27 \({}^{\circ}\)C and humidity of 60%. The session started with an assessment of the swimmers' anthropometric characteristics while they were wearing only a textile swimsuit and a cap. Body mass (in kg) was assessed using a scale (TANITA, BC-730, Amsterdam, The Netherlands), while body height (in m) was measured using a digital stadiometer (SECA, 242, Hamburg, Germany). Swimmers were marked at four anatomical points on the right sagittal plane (acromion, hip, knee, ankle) using an oil-based black makeup and waterproof wax cream suitable for aquatic environments (Make-Up Pure Cream, 101, Grimas, Utrecht, The Netherlands). Then, the swimmers completed a standardized warm-up of 200 m of easy swimming--100 of kicking, 4 \(\times\) 25 m with the increasing speed between each 25 m set--and 100 m at a recovery pace. After a passive rest of 10 min, the swimmers were randomly assigned to complete the in-water protocol (Figure 1), which consisted of three tests for kinematic and kinetic measurements, each followed by 10 min of recovery: (i) 25 m maximal front crawl; (ii) 25 m towing; and (iii) 20 s full tethered kicking. In the first test (Figure 1, panel A), the swimmers performed a 25 m maximal-effort front crawl starting with a push-off against the wall after an audible signal, maintaining their normal breathing pattern. Each swimmer performed this test alone, without any other disturbances in the nearest lanes. The 25 m time (T25, in s) was manually assessed by a certified coach using a stopwatch (FINIS 3 \(\times\) 100, Finis Inc.) and considered the time taken (in s) to cover 25 m and the mean velocity (v, in m/s) was estimated thereafter. The stroke rate (SR, in Hz) was assessed using a frequency chronometer (FINIS 3 \(\times\) 300, Finis Inc.) activated over three consecutive stroke cycles. The stroke length (SL, in m) was then estimated (SL = v/SR), along with the stroke index (SI, in m\({}^{2}\)/s) (SI = v\(\cdot\)SL), as previously described [15]. This test was recorded on video (at a frequency of 120 Hz) in the sagittal plane (right side) with a camera (Go Pro 6, resolution 1920 \(\times\) 1080 pixels, San Mateo, CA, USA) mounted on a rigid iron fixed at 0.26 m, providing a view below the water's surface. Figure 1: Experimental procedures and testing order. The system was positioned at around 15 m from the starting wall, on the side of the pool, perpendicular to the line of movement and 5 m away from the swimmer, providing a range of views between the 11 th and 24 th m. The images were stored on a USB memory stick, enabling data to be collected and processed using a computer and a video annotation tool (Kinovea(r), v. 0.8.15). All the kinematic variables were assessed over two non-respiratory consecutive stroke cycles between the 11 th and 24 th m using the \"angle\" or \"time\" options from the software and the mean values from these cycles were considered for further analysis. The trunk inclination (TI, in \({}^{\circ}\)) was taken at the moment where the swimmer's right hand started the entry phase of the stroke cycle and was determined to be the angle between the shoulder (acromion), hip segment (greater trochanter) and the horizontal, as previously described [3]. For the lower limbs' kinematics, the maximum (KneeMax, in \({}^{\circ}\)) and minimum (KneeMin, in \({}^{\circ}\)) knee angles (increasing with extension and reducing with flexion), as well as the knee's range of motion (KneeROM, in \({}^{\circ}\)), were retrieved from the right side. The deepest point of the feet in relation to the water surface (full extension of the lower limb) and the nearest point to the water surface (maximum flexion of the lower limb) were considered as the instantaneous timings for KneeMax and KneeMin measurements, respectively.