Ski racer Thea Waldleben measures g-forces with the help of MSR165 data loggers
How high are the acceleration forces acting on the knees of an alpine ski racer during skiing? This question was investigated by the reigning Swiss junior downhill champion, Thea Waldleben, in her Matura thesis. With the help of data loggers, the athlete analyzed the load and behavior of the knees during skiing under various influences.
Thea Waldleben, who is also successful in the Super-G discipline, trains in the women's squad of the Swiss-Ski Alpine Skiing Center and attends the Swiss Sports School Engelberg (SSE). The educational institution, which is certified by Swiss Olympic, has made a name for itself as a talent factory for ambitious young athletes and has already produced prominent athletes, particularly in alpine skiing, including Olympic gold medal winner Dominique Gisin and World Cup medal winner Wendy Holdener. As part of her Matura thesis, Thea Waldleben, who is supported by Swiss ski manufacturer Stöckli, asked herself what stresses her knees are exposed to during ski racing.
Mini-Logger MSR165 measures g-forces in all three axes
The athlete used the MSR165 data logger for her study. This data logger, which specializes in applications for recording oscillation, shock and vibration, is waterproof and only the size of a thumb, making it particularly suitable for measurements on the body. The mini logger has a highly sensitive digital sensor that can take up to 1600 measurements per second in the acceleration range in all three axes. Depending on the configuration, the MSR165 has a memory capacity of up to one billion measured values. Using a sensor (measuring range ±15 g or ±200 g), Ms. Waldleben was able to record the acceleration forces to which her knees were subjected. As the housing of the data logger for the measurements on the body had to be even lighter than the aluminum design housing of the MSR165 standard models, which is designed for industrial applications, the ski racer was provided with a special version of the logger in a lighter SmartCase. The data loggers were attached with Velcro straps directly below the knee joint on the tibial plateau and above the ski boot.
Execution of the measurements
All measurements were carried out while skiing freely without a turn or in the gates with a turn. The various measurement blocks were carried out on the same day in a short period of time. The slopes were selected according to their characteristics in terms of inclination and evenness in order to achieve comparability of the turns. The behavior of the athlete's knee in the X-, Y- and Z-axis and the mean value were measured and evaluated for various influencing factors using several measurements. In the tests, the knee load was analyzed during skiing with different skis (slalom and giant slalom), changing slope conditions and the influence of ski boot hardness. For her study, Ms. Waldleben worked with a frequency of 100 measurements per second in all three directions in order to detect abruptly changing loads on the knee.
Brief analysis of the measurement results
Thea Waldleben's measurements show large g-forces, particularly in the Y-axis. The smaller the hardness flex of the ski boot and the softer and more unsteady the slope conditions, the more unsteady the knee behaves in all directions of movement and the load increases. In free skiing, loads on the knee were measured to be on average up to three times the body weight. In predetermined radii in the slalom and giant slalom, even greater forces were measured, up to two to three times this value.
Counteracting the risk of injury when skiing
Knee injuries occur very frequently when skiing. In order to train preventively and to cope with the high forces measured, especially in racing, it is very important to train knee stability in all directions of movement. Pure strength training alone is not enough. It must be trained very specifically for these rapidly changing maximum forces. This can be trained, for example, by performing exercises on moving surfaces with and without weight loads or by walking on a slackline.
