Original ResearchValidation of an inertial measurement unit for the measurement of jump count and height
Introduction
There is a growing body of literature surrounding the use of microtechnology for the detection of sport specific movements (Chambers, Gabbett, Cole, & Beard, 2015). Wearable sensors can include accelerometers, magnetometers and gyroscopes, with several commercially available inertial measurements units (IMU's) being comprised of a combination of sensors. IMU's allow for the measurement of movement in three dimensions in real-time. The quantification of sport movements permits sport staff to improve injury prevention, physical preparation and technical and tactical analysis within their sport (Gabbett et al., 2016, Hulin et al., 2015). Although there has been an increase in the use and availability of IMU's there is a paucity of research surrounding their validity and reliability in sport specific contexts (Boyd et al., 2011, Chambers et al., 2015).
Recent research has identified that jump frequency, measured as the number of jumps per hour of training or match play, differs substantially between volleyball players (regardless of similarity of court positions) (Bahr & Bahr, 2014). This finding suggests that exposure hours or minutes are an unreliable indicator of jump load and that an individual-based, precise measure of jump load is required. A potential alternative indicator of jump load is visual jump count, however this approach is time consuming and lacks utility in sports in which several players may jump at the same time. For example, Bahr & Bahr report that 12 h of jump count analysis was required for 2 h of volleyball match play (Bahr & Bahr, 2014). An additional disadvantage of visual inspection is that jump height (an important component of jump load) cannot be accurately quantified visually.
Due to limitations with exposure hours and visual inspection as a means to quantify jump load it would be beneficial to have a valid method for the quantification of jump exposure. Jarning, Mok, Hansen, and Bahr (2015) attempted to use accelerometers to count volleyball jump load however, their validation study found that the device had poor specificity as it failed to differentiate jumping from other volleyball specific movements, such as diving. Recently, IMU's have been developed to track jump load in real word contexts however, to date no IMU device has been validated for the assessment of jump load (Chambers et al., 2015). If such a device could accurately capture both jump frequency and jump height it could provide a field measure of individualized jump load, which would have significant implications for injury prevention and strength and conditioning.
The primary objective of this study was to validate a combined accelerometer gyroscope IMU (VERT; version 2.0, Mayfonk Inc., Fort Lauderdale, FL, USA) for total jump count against visual inspection in a structured practice and game-specific context. A second objective was to validate the device for jump height against the gold standard of 3-D motion analysis.
Section snippets
Participants
Study participants included 13 male adolescent volleyball players recruited from an elite club volleyball team in Calgary, Alberta, Canada. All participants provided consent and assent to participate. Potential participants were excluded if they possessed an injury at the time of the study that restricted their ability to fully participate in match play.
Inertial measurement unit
Participants completed all activities while wearing a commercially available IMU device (VERT; version 2.0, Mayfonk Inc., Fort Lauderdale, FL,
Participant characteristics
Participants had a mean age of 16.1 years (95%CI; 15.1, 17.1), mean height 188 cm (95%CI; 175, 200) and mean mass of 75 kg (95%CI; 59, 90). All 13 male participants completed the jump height data collection, while only 12 (two teams of six players) completed the volleyball match and controlled practice data collection.
Jump count
Although participants were instructed to perform exactly 60 jumping activities, upon video review it was discovered that some performed additional jumps. These additional jumps
Discussion
This is the first study to assess the validity of a novel IMU device, which combines an accelerometer with a gyroscope, for the collection of jump count and jump height. During structured practice, the IMU performed perfectly capturing only jumping activities, which has been a limitation with previous accelerometer only devices (Jarning et al., 2015). Further, the device demonstrated a sensitivity of 97% suggesting it is sufficiently accurate for use as a field-based measure of jump frequency.
Conclusion
This is the first study to demonstrate that an IMU device is capable of accurately measuring jump load in a practical setting. The resulting information collected by this device will allow for novel approaches in the prevention of overuse injuries and the maximization of performance. Using an IMU that can accurately capture jump data provides a tremendous opportunity to further the scientific understanding of the sport specific movements in a multitude of jumping dominated sports.
Conflict of interest
None declared.
Ethical approval
Ethical approval was provided by the Conjoint Health Research Ethics Board. Consent and assent to participate was collected from all participants.
Funding
The Sport Injury Prevention Research Centre is funded by the by an International Olympic Committee Research Centre Award that made this research possible. Mayfonk Incorporated (Fort Lauderdale, FL, USA) provided the 12 VERT devices used in this study at no charge.
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