simulation of snowboarding falls: the back edge catch · 2016-10-05 · snowboarding injuries •...

Simulation of Snowboarding Falls: The Back Edge Catch

Nicholas Yang, PhD, PE Irving Scher, PhD, PE

Lenka Stepan, PhD Jasper Shealy, PhD, CPE

Snowboarding Injuries

• Shealy et al., 2015 – 2010/2011 NSAA incident report

data – Head injuries = 13.4% of all

injuries – Suspected concussion = 11.4%

of all injuries

Linear Acceleration Injuries

Linear Acceleration

• Skull fracture

• Coup brain injuries Near site of impact

• Contrecoup brain injuries Opposite side from impact

Localized injuries

Rotational Acceleration Injuries

Angular Acceleration

Shearing injuries – Bridging vein rupture

(subdural hematoma) – Diffuse axonal injury

Injury not necessarily at or opposite to site of impact

Diffuse injury

Back Edge Catch

The majority of severe snowboarding head injuries were caused by the

�opposite-edge phenomenon��

where the snowboarder falls backwards and contacts the occiput.

— Nakaguchi et al. (2002)

Previous Research – Scher et al., 2005

•  Physical testing of back edge catch

•  Hybrid III 50th percentile male

•  Hard and soft snow

•  30 kph (18.6 mph) impact speed

•  Measured linear head acceleration

Objective

Develop a model to simulate a snowboarding back edge catch

Methods • Developed snowboarder model – LS DYNA coupling

• Validate kinematics to video of a real world back edge catch – Modify joint friction torque

• Validate head-snow contact from Scher et al., 2010 ATD experiments

• Human Body Model

(HBM) – 50th percentile male

• LS DYNA Coupling – Snowboard meshed

in LS DYNA

Snowboarder Virtual Model

Back Edge Catch Simulation •  Initial snowboarder speed –  17.1 kph (10.5 mph) –  Parallel to surface

•  8 degree slope

Back Edge Catch Video

Kinematics Comparison

Unmodified HBM

Modify HBM Joint Friction Torques

Used joint friction torques determined during isometric conditions – Sandler and Robinovitch, 2001 •  Lower extremity maximum joint friction torque – Ankle: 90 N-m – Knee: 155 N-m

– Hip: 130 N-m

– van der Horst et al., 1997 •  Cervical spine maximum joint friction torque –  20 - 44 N-m depending on cervical spine level

Simulations with Modified Joint Friction Torques

Max Torque 25% of Max Torque

Kinematics Matched to Video Modified HBM 25% max joint friction torque

Validate Head-Snow Contact Properties

• Define snow surface characteristics

• Compare head injury metrics to physical testing – Scher et al., 2005

Snow Contact Characteristics •  Federolf et al., 2006 –  Measured resistance pressure

of snow •  Hard, icy snow •  Average snow •  Soft groomed snow

•  Modeled as FE-FE contact –  Defined surface char. –  Hard, icy snow –  Soft groomed snow

Compare Injury Metrics to Testing Simulate Scher et al., 2005

• Snowboarder HBM with modified joint friction torques

• 20 degree slope

• ~30 kph velocity

• Hard and soft snow

Examined Fall Kinematics

Normal HBM

Modified Joint Friction Torque

Results – Hard Icy Snow Peak Resultant Head Acceleration

Linear

G Angular rad/sec2

Scher et al., 2005 391 ± 105 --

MADYMO HBM 485 23,602

MADYMO modified HBM 379 21,245

Results – Soft Snow Peak Resultant Head Acceleration

Linear

G Angular rad/sec2

Scher et al., 2005 182 ± 105 --

MADYMO HBM 251 10,368

MADYMO modified HBM 147 8,882

Conclusions

Validated snowboarder back edge catch fall simulation -  Matched real world fall kinematics

by modifying joint torques

-  Similar head linear accelerations to physical back edge catch tests

Further Research

• Joint Torques – Optimize % of max friction torque for

each joint – Sensitivity analysis – Lumbar and thoracic spine

• Match videos of higher speed falls

Relative Velocity Angle - Jumps

Normal Velocity

Tangential Velocity

Resultant Velocity

2014 Olympics: Back Edge Catch

2014 Olympics: Back Edge Catch

THANK YOU

Relative Velocity Angle - Jumps

10 degrees 30 degrees