The Use of Triaxial Accelerometry for Measuring Stride Parameters and Vertical Stiffness in Team-Sport Athletes

Inertial Measurement Units (IMUs) provide a means for analysing running gait in the field without the need for extensive lab-based equipment. These sensors have been validated for use on the lower limbs and lumbosacral region but have not been extensively validated at other body regions. In team-sport, athletes commonly wear global navigation satellite system (GNSS) units on the thoracic spine to quantify distance and speed. These GNSS units also contain IMUs which may allow the measurement of running gait characteristics, such as contact time, step length and vertical stiffness (Kvert), that GNSS is unable to capture. These data provide more granular information on running activity that can be used to provide insight into the mechanistic changes in movement strategy, such as those occurring in the presence of fatigue, that may precede, or occur independently of any modification in distance and speed. Given IMUs are already available in GNSS units, the thoracic spine site is potentially attractive for practitioners as it provides the possibility of measuring distance and speed from GNSS and running gait from inertial sensors to provide a comprehensive analysis of running activity all from the one device. However, the validity and reliability of thoracic-mounted IMUs to derive a range of gait characteristics across multiple running speeds has not been thoroughly explored. Therefore, the overarching aim of this thesis was to determine the validity and reliability of running gait characteristics obtained from IMUs worn on the thoracic spine and assess their effectiveness for the assessment of fatigue-induced changes.
study 1 demonstrated that IMU placement site is not a limiting factor to the measurement of running gait, which can in fact be validly and reliably measured from multiple locations (foot, tibia and lumbar spine). The results from Study 2 confirm this as it was shown thoracic-worn IMUs, including those contained in GNSS units, are accurate for event detection (a previously unreported finding) and are valid and reliable for deriving a range of spatiotemporal gait characteristics, vGRFpeak and Kvert at different running speeds. Practitioners do not need to use additional sensors at other sites to analyse running gait but can instead take advantage of commonly worn sensors contained in GNSS units. These are also sensitive to detecting fatigue, as demonstrated in Study 3 which showed reductions in Kvert during sprinting. This result is consistent with the fatigue-induced changes of Kvert seen in other lab-based studies, and it provides evidence of the changes that occur in running at a mechanistic level that have so far not been quantifiable from GNSS-embedded IMUs. This allows for potential practical applications such as monitoring changes in Kvert and other metrics within training and matches which may reduce the requirement of additional testing protocols (e.g., CMJ) to assess fatigue. In addition, running gait characteristics, such as vGRFpeak, may be useful for informing the delivery of lower-limb injury rehabilitation or to assess changes in movement (running) strategy following concussion. Overall, the findings presented in this work support the use of IMUs contained within GNSS units for the analysis of running gait in the field.

This work © 2023, Benjamin Horsley.