# At the End of a Slippery Slope: A Pilot Study of Deceleration Mats for Snow Tubing
## 2 Materials and Methods
### Test Equipment  
Participant kinematics and body motions were measured using an instrumented body suit (MVN Link, Xsens Technologies, Enschede, The Netherlands) containing 17 inertial measurement units (IMUs) that were worn under snowswport clothing. Each IMU contained a tri-axial set of linear accelerometers (range: \(\pm\)160 m/s\({}^{2}\); noise: 0.003 m/s\({}^{2}\)/\(\sqrt{\text{Hz}}\)), angular rate sensors (range: \(\pm\)2000 \({}^{\circ}\)/s; noise: 0.05\({}^{\circ}\)/s/\(\sqrt{\text{Hz}}\)), and magnetometers. The data from each sensor were recorded at 240 Hz and processed using the Xsens MVN Studio BIOMECH software package. The output from this system included kinematics (acceleration and angular rate components) of the body segments and the center of mass (COM) location. In addition to the kinematic body suit, the participants were also instrumented with a GPS system that measured global position near the thoracolumbar spine and speed at 5 Hz (G2X Extreme Data Logger, Racepak, Rancho Santa Margarita, CA, USA); the GPS unit also had a set of linear accelerometers (range: \(\pm\)98.1 m/s\({}^{2}\); noise: 0.005 m/s\({}^{2}\)) that recorded at 100 Hz. These additional sensors were placed in a west that did not disturb the snow tube wider; see Figure 1.  
Four photogates (PR1A, Alge Timing, Lustenau, Austria) were placed near the bottom of the tubing run to determine the time when the rider reached the photogate locations. Two photogates were placed 0.35 m uphill of the run-out area. The other two photogates were placed in the run-out area, with the one furthest downhill located at the uphill edge of the deceleration mats. Each deceleration mat was approximately 1.52 m long, 0.91 m wide, and 1.6 cm thick. To increase the likelihood that the snow tube would ride fully over the mats, two deceleration mats were used to span the tubing run (in the left-to-right direction); see Figure 2c,d. For the analysis, a first and second set of mats were used along the direction of travel; these sets were separated by approximately 0.3 m and 0.8 m of snow surface when the mats were flat and folded, respectively.  
Figure 1: Participant riding position on a snow tube. The participant is wearing the kinematic body suit under his winter clothing.  
Figure 2: (**a**) Close-up view of a deceleration mat showing the “ribs” on the top surface (**b**) Close-up view of a deceleration mat showing the “projections.” (Bottom row) View uphill of the tubing lane, with the first set of deceleration mats in the following conditions: (**c**) _flat_, _ribs_ and (**d**) _folded_, _projections_ condition. Two mats (left to right) on the tubing run were used to increase the likelihood that the snow tube would ride fully over the mats.  
Data from the photogates were sampled at 2400 Hz (Nanoslice, Diversified Technical Systems, Seal Beach, CA, USA). Using the timing and the distances between photogates, the average speeds for the snow tube rider were calculated: these speeds matched well those recorded by the GPS system at the beginning of the run-out area and the speed at run-out entry presented will be from the GPS system. All systems were synchronized using remote camera triggers (Pulse II, PocketWizard USA, Shelburne, VT, USA) and impulses measured by the accelerometers of each system; synchronization allowed for the determination of kinematics at locations relative to the uphill edge of the deceleration mats. For each test trial, real-time video was recorded at 29.97 frames per second at a resolution of 1920 \(\times\) 1080 (HDR-XR500V, Sony, Japan).