3D Tibial Acceleration and Consideration of 3D Angular Motion Using IMUs on Peak Tibial Acceleration and Impulse in Running

Purpose: Peak tibial acceleration (PTA) is defined as the peak acceleration occurring shortly after initial contact, often used as an indirect measure of tibial load. As the tibia is a rotating segment around the ankle, angular velocity and angular acceleration should be included in PTA. This study aimed to quantify 3D tibial acceleration components over two different sensor locations and three running speeds, to get a better understanding of the influence of centripetal and tangential accelerations on PTA typically measured in running. Furthermore it explores tibial impulse as alternative surrogate measure for tibial load.

Methods: 15 participants ran 90 seconds on a treadmill at 2.8, 3.3, and 3.9 m·s-1, with IMUs located distally and proximally on the tibia.

Results: Without the inclusion of rotational accelerations and gravity, no significant difference was found between axial PTA between both IMU locations, while in the tangential sagittal plane axis there was a significant difference. Inclusion of rotational accelerations and gravity resulted in similar PTA estimates at the ankle for both IMUs, and caused a significant difference between PTA based on the distal IMU and PTA at the ankle. The impulse showed more consistent results between the proximal and distal IMU location compared to axial PTA.

Conclusions: Rotational acceleration of the tibia during stance differently impacted PTA measured proximally as well as distally at the tibia, indicating that rotational acceleration and gravity should be included in PTA estimates. Furthermore, peak acceleration values (such as PTA) are not always reliable when using IMUs due to inconsistent PTA proximally compared to distally on an individual level. Instead, impulse seems to be a more consistent surrogate measure for the tibial load.