about the WSSA
John Seifert, PhD
The WSSA is a scientific and educational center of excellence for the advancement of winter sport performance and safety.
John Seifert, PhD is the Director of the WSSA.
indoor alpine skiing
How similar is indoor skiing to the real thing?
Background. Indoor carpet skiing (picture, right) provides an optimal setting to study alpine ski turning technique while controlling for environmental and surface conditions, slope inclination (pitch) and speed. However, the performance similarities between indoor and outdoor skiing are currently unknown. The purpose of this study was to compare 3D body and leg joint motion measurements during indoor and outdoor skiing.
Recent Findings. The analysis phase for this project has only recently started. The graphical illustrations below are from one participant during indoor skiing (left) at a 20 deg pitch while performing narrow turns (middle) and wide turns (right). The middle and right figures are the 3D knee joint motions averaged over turn time for the left (top figures) and right (bottom figures) legs. Data reduction and subsequent comparison with outdoor skiing are currently in process.
More Scientific Resources.
turning performance and balance
Can directional compression tights influence skiing performance?
Dany Blake, MS, CSCS, Director of Human Performance for the RMCSR, presented research at the International Society of Ski Safety (2019) investigating the influence of directional compression tights on ground reaction forces and dynamic balance during alpine skiing on a course with standardized turns.
Background. Directional compression (DCP) tights have been found to influence trunk kinematics and the location of the applied ground reaction force (GRF) during alpine skiing (Simons et al., 2017). Due to the trunk’s high segmental mass, a change in trunk flexion angle may also influence dynamic stability. The purpose of this study was to determine the effects of DCP on GRF and dynamic stability during alpine skiing.
Pressure insoles (Pedar, Novel, Munich, Germany) measured (100 Hz) the normal GRF and center of pressure (CoP) of nine elite collegiate racers during eight consecutive double-turns on a slalom course while wearing directional compression (DCP) or standard compression (SCP) tights. Mean (±SE) maximum GRF (GRFmax), GRF impulse (GRFimp) and CoP velocity (CoPvel) were calculated during four turn phases: Initiation (0-20%, P1); Steering I (21-50%, P2); Steering II (51-80%, P3); and Completion (81-100%, P4). Turn initiation was determined via the functional minima of the summed GRFs. A three-way repeated measures ANOVA was used to determine the effects of compression (DCP, SCP), turning phase (P1-P4) and downhill leg (dominant (DOM), non-dominant (NON)) on the dependent variables (p=.05).
Recent Findings. The COPvel and GRF values were the largest during P2 and P3 indicating that dynamic balance was challenged during the application of large GRF. The NON leg demonstrated larger CoPvel in P4 suggesting laterality in the neuromuscular control of dynamic stability favoring the DOM leg. Compared to SCP, DCP reduced the GRF values on average by 8% but did not alter CoPvel or the asymmetry measured between downhill legs during P4 at the end of the turn. These results indicate DCP reduced the GRF variables but preserved dynamic stability during alpine skiing.
More Scientific Resources.
1. Simons, C.J., Decker, M.J., Seifert, J.G., Shelburne, K.B., Sterett, W.I., Davidson, B.S., 2017, Redistribution of lower-extremity joint moments during alpine skiing. Science and Skiing, Volume 7, Pages 188-196.
2. Website: www.opedix.com
Directional compression tights by Opedix (oh-pee-dix).
WIDE SKIS
Are wide skis an injury risk factor?
John Seifert, PhD (picture, right), an Exercise Physiologist at Montana State University, performed an alpine skiing research project at Squaw Valley with Ron Kipp PhD and the RMCSR investigating the difference in turn technique and muscle activity when using wide powder skis (>90mm underfoot width) and regulation slalom skis (~65 mm underfoot width) during skiing on a course with standardized turns.
Background. It has been widely reported that muscle activity increases when skiing on wide powder skis compared to skiing on slalom regulation skis on groomed runs. Wide skis were originally designed to be skied in powder snow conditions. In recent years, it has been observed that skiers have been using the wide skis for all conditions including groomed snow. Junior racers are commonly seen using wide skis while skiing outside of the racing and training area. A major concern is that junior skiers may be developing a technique of muscle activity patterns when skiing wide skis that may be different than the technique necessary for racing. This could lead to poor performance, increased fatigue, or injury while racing.
Recent Findings. Perceptions of performance and effort are factors that can add or detract from learning a movement. Feeling confident, being aggressive, and skiing on line was lower when performing with wide skis. These perceptions can impact the timing and tactics of the run, perhaps by increasing inhibition and creating less effective movements. Read more about these findings in the scientific abstract below: Seifert ECSS 2019
More Scientific Resources.
1. The Waist Width of Skis Influences the Kinematics of the Knee Joint in Alpine Skiing
2. Does Ski Width Influence Muscle Action in an Elite Skier? A Case Study.
Video
Alpine Skiing biomechanics
Wearable Sensors for Motion Measurement
Coming soon
Ground Reaction Forces
Ground Reaction Forces
Ground Reaction Forces
The average vertical ground reaction force (top) and the center of pressure (fore-aft, middle; medial-lateral, bottom) for two ski conditions during the four phases of an alpine ski turn.
Joint Kinematics
Ground Reaction Forces
Ground Reaction Forces
The average knee angle for two conditions during during the four phases of an alpine ski turn.
Joint Kinetics
Ground Reaction Forces
Joint Kinetics
The hip and knee joint moments for two conditions during a double ski turn.
Personal protective gear (PPG) for alpine skiing
Should a dual lateral release ski binding be considered PPG?
Background. Workplace injury rates, worker compensation costs and additional medical and administrative costs, including physical rehabilitation and the training or hiring of additional employees, places an estimated $85.1 million economic burden on the 481 U.S. ski areas. This annual burden has amplified the need for better ski equipment that limits the injurious forces applied to the body during twisting falls with or without an accompanying collision (ie, obstacle, another skier).
A novel ski binding designed with a dual lateral release mechanism (picture, right; KneeBinding Inc., Stowe, VT) may limit these injurious forces by increasing the probability of the boot releasing from the ski during a twisting fall and thus provide a practical solution for reducing workplace injuries. The purpose of this study was to determine the influence of a novel, commercially available ski binding on injury risk in professional ski instructors.
A total of 170 professional ski instructors from three ski areas located in the Rocky Mountains participated in a prospective randomized controlled research study investigating the effects of ski bindings with a single (LR1) versus dual (LR2) lateral release mechanism on injury risk over two consecutive ski seasons (2016-2017 and 2017-2018).
Recent Findings. The results of this study found a commercially available ski binding with a dual lateral release mechanism can reduce workplace injuries in the ski industry. Ski instructors were found to have a 3.6 and 4.8 times lower risk of body and knee injury events compared to ski instructors not using this intervention product. These results are encouraging and may have implications for both ski instructors and ski areas.
More Scientific Resources.
1. Effect of Alpine Ski Bindings with Single versus Dual Lateral Release Mechanisms on Injury Risk in Professional Ski Instructors. (Coming Soon)
2. Website: www.kneebinding.com
PSIA Technology taskforce
RMCSR Joins the PSIA Technology Taskforce
Members of the Professional Ski Instructors of America (PSIA), Microsoft and the RMCSR joined forces to perform collaborative research to study alpine ski biomechanics and enhance the instruction and education programs of the PSIA. Video (below) with visualizations of the body's center of mass during alpine skiing created by Ron LeMaster.
