Abstract
This study explored the use of body worn sensors to evaluate the vibrations that act on the human body in alpine ski racing from a general and a back overuse injury prevention perspective. In the course of a biomechanical field experiment, six male European Cup-level athletes each performed two runs on a typical giant slalom (GS) and slalom (SL) course, resulting in a total of 192 analyzed turns. Three-dimensional accelerations were measured by six inertial measurement units placed on the right and left shanks, right and left thighs, sacrum, and sternum. Based on these data, power spectral density (PSD; i.e., the signal's power distribution over frequency) was determined for all segments analyzed. Additionally, as a measure expressing the severity of vibration exposure, root-mean-square (RMS) acceleration acting on the lower back was calculated based on the inertial acceleration along the sacrum's longitudinal axis. In both GS and SL skiing, the PSD values of the vibrations acting at the shank were found to be largest for frequencies below 30 Hz. While being transmitted through the body, these vibrations were successively attenuated by the knee and hip joint. At the lower back (i.e., sacrum sensor), PSD values were especially pronounced for frequencies between 4 and 10 Hz, whereas a corresponding comparison between GS and SL revealed higher PSD values and larger RMS values for GS. Because vibrations in this particular range (i.e., 4 to 10 Hz) include the spine's resonant frequency and are known to increase the risk of structural deteriorations/abnormalities of the spine, they may be considered potential components of mechanisms leading to overuse injuries of the back in alpine ski racing. Accordingly, any measure to control and/or reduce such skiing-related vibrations to a minimum should be recognized and applied. In this connection, wearable sensor technologies might help to better monitor and manage the overall back overuse-relevant vibration exposure of athletes in regular training and or competition settings in the near future.
Highlights
On the topic of the relationship between training load and sports injuries, there is emerging evidence that poor load management is a major injury risk factor (Drew and Finch, 2016)
In both giant slalom (GS) and SL, the power spectral density (PSD) values of the vibrations acting on the shank were largest for frequencies below 30 Hz
Knowing that vibrations of those frequencies are the most damaging vibrations for spinal structures and increase the risks of developing low back pain (Hill et al, 2009; Burström et al, 2015), they may be considered potential components of mechanisms leading to overuse injuries of the back in alpine ski racing
Summary
On the topic of the relationship between training load and sports injuries, there is emerging evidence that poor load management (i.e., an insufficient balance between loading and recovery) is a major injury risk factor (Drew and Finch, 2016). Monitoring the external loads that act on the human body is key to better understanding the occurrence of (and potentially to Vibrations in Alpine Ski Racing avoid) injuries in competitive sports (Soligard et al, 2016) In this context, body worn inertial measurement units (IMU) may offer a pervasive way to measure both load-related body postures, as well as vibrations acting on the human body during outdoor sports activities (Kim et al, 1993; Chardonnens et al, 2013; Seel et al, 2014; Fasel et al, 2017). Their practical usefulness will be demonstrated through the sport of alpine ski racing
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